[dev.boringcrypto.go1.16] all: merge go1.16.3 into dev.boringcrypto.go1.16

Change-Id: I037c70c43855beee7f2f817cf4304133dfe2ecfa

36 files changed, 778 insertions, 129 deletions

diff --git a/misc/cgo/testplugin/plugin_test.go b/misc/cgo/testplugin/plugin_test.go
index 2d991012c8..8869528015 100644
--- a/misc/cgo/testplugin/plugin_test.go
+++ b/misc/cgo/testplugin/plugin_test.go
@@ -209,3 +209,10 @@ func TestMethod2(t *testing.T) {
 	goCmd(t, "build", "-o", "method2.exe", "./method2/main.go")
 	run(t, "./method2.exe")
 }
+
+func TestIssue44956(t *testing.T) {
+	goCmd(t, "build", "-buildmode=plugin", "-o", "issue44956p1.so", "./issue44956/plugin1.go")
+	goCmd(t, "build", "-buildmode=plugin", "-o", "issue44956p2.so", "./issue44956/plugin2.go")
+	goCmd(t, "build", "-o", "issue44956.exe", "./issue44956/main.go")
+	run(t, "./issue44956.exe")
+}
diff --git a/misc/cgo/testplugin/testdata/issue44956/base/base.go b/misc/cgo/testplugin/testdata/issue44956/base/base.go
new file mode 100644
index 0000000000..609aa0dff4
--- /dev/null
+++ b/misc/cgo/testplugin/testdata/issue44956/base/base.go
@@ -0,0 +1,7 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package base
+
+var X = &map[int]int{123: 456}
diff --git a/misc/cgo/testplugin/testdata/issue44956/main.go b/misc/cgo/testplugin/testdata/issue44956/main.go
new file mode 100644
index 0000000000..287a60585e
--- /dev/null
+++ b/misc/cgo/testplugin/testdata/issue44956/main.go
@@ -0,0 +1,47 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Issue 44956: writable static temp is not exported correctly.
+// In the test below, package base is
+//
+//     X = &map{...}
+//
+// which compiles to
+//
+//     X = &stmp           // static
+//     stmp = makemap(...) // in init function
+//
+// plugin1 and plugin2 both import base. plugin1 doesn't use
+// base.X, so that symbol is deadcoded in plugin1.
+//
+// plugin1 is loaded first. base.init runs at that point, which
+// initialize base.stmp.
+//
+// plugin2 is then loaded. base.init already ran, so it doesn't run
+// again. When base.stmp is not exported, plugin2's base.X points to
+// its own private base.stmp, which is not initialized, fail.
+
+package main
+
+import "plugin"
+
+func main() {
+	_, err := plugin.Open("issue44956p1.so")
+	if err != nil {
+		panic("FAIL")
+	}
+
+	p2, err := plugin.Open("issue44956p2.so")
+	if err != nil {
+		panic("FAIL")
+	}
+	f, err := p2.Lookup("F")
+	if err != nil {
+		panic("FAIL")
+	}
+	x := f.(func() *map[int]int)()
+	if x == nil || (*x)[123] != 456 {
+		panic("FAIL")
+	}
+}
diff --git a/misc/cgo/testplugin/testdata/issue44956/plugin1.go b/misc/cgo/testplugin/testdata/issue44956/plugin1.go
new file mode 100644
index 0000000000..499fa31abf
--- /dev/null
+++ b/misc/cgo/testplugin/testdata/issue44956/plugin1.go
@@ -0,0 +1,9 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import _ "testplugin/issue44956/base"
+
+func main() {}
diff --git a/misc/cgo/testplugin/testdata/issue44956/plugin2.go b/misc/cgo/testplugin/testdata/issue44956/plugin2.go
new file mode 100644
index 0000000000..a73542ca71
--- /dev/null
+++ b/misc/cgo/testplugin/testdata/issue44956/plugin2.go
@@ -0,0 +1,11 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import "testplugin/issue44956/base"
+
+func F() *map[int]int { return base.X }
+
+func main() {}
diff --git a/src/cmd/compile/internal/gc/sinit.go b/src/cmd/compile/internal/gc/sinit.go
index 212fcc022d..4d0837bc74 100644
--- a/src/cmd/compile/internal/gc/sinit.go
+++ b/src/cmd/compile/internal/gc/sinit.go
@@ -363,15 +363,15 @@ func staticname(t *types.Type) *Node {
 	n := newname(lookup(fmt.Sprintf("%s%d", obj.StaticNamePref, statuniqgen)))
 	statuniqgen++
 	addvar(n, t, PEXTERN)
-	n.Sym.Linksym().Set(obj.AttrLocal, true)
 	return n
 }
 
-// readonlystaticname returns a name backed by a (writable) static data symbol.
+// readonlystaticname returns a name backed by a read-only static data symbol.
 func readonlystaticname(t *types.Type) *Node {
 	n := staticname(t)
 	n.MarkReadonly()
 	n.Sym.Linksym().Set(obj.AttrContentAddressable, true)
+	n.Sym.Linksym().Set(obj.AttrLocal, true)
 	return n
 }
 
diff --git a/src/cmd/compile/internal/ssa/gen/AMD64.rules b/src/cmd/compile/internal/ssa/gen/AMD64.rules
index a866a967b9..5de1e1ec31 100644
--- a/src/cmd/compile/internal/ssa/gen/AMD64.rules
+++ b/src/cmd/compile/internal/ssa/gen/AMD64.rules
@@ -623,6 +623,14 @@
 // Recognize bit setting (a |= 1<<b) and toggling (a ^= 1<<b)
 (OR(Q|L) (SHL(Q|L) (MOV(Q|L)const [1]) y) x) => (BTS(Q|L) x y)
 (XOR(Q|L) (SHL(Q|L) (MOV(Q|L)const [1]) y) x) => (BTC(Q|L) x y)
+(ORLmodify [off] {sym} ptr s:(SHLL (MOVLconst [1]) <t> x) mem) =>
+	(BTSLmodify [off] {sym} ptr (ANDLconst <t> [31] x) mem)
+(ORQmodify [off] {sym} ptr s:(SHLQ (MOVQconst [1]) <t> x) mem) =>
+	(BTSQmodify [off] {sym} ptr (ANDQconst <t> [63] x) mem)
+(XORLmodify [off] {sym} ptr s:(SHLL (MOVLconst [1]) <t> x) mem) =>
+	(BTCLmodify [off] {sym} ptr (ANDLconst <t> [31] x) mem)
+(XORQmodify [off] {sym} ptr s:(SHLQ (MOVQconst [1]) <t> x) mem) =>
+	(BTCQmodify [off] {sym} ptr (ANDQconst <t> [63] x) mem)
 
 // Convert ORconst into BTS, if the code gets smaller, with boundary being
 // (ORL $40,AX is 3 bytes, ORL $80,AX is 6 bytes).
@@ -645,6 +653,10 @@
     => (BTRQconst [int8(log64(^c))] x)
 (ANDL (MOVLconst [c]) x) && isUint32PowerOfTwo(int64(^c)) && uint64(^c) >= 128
     => (BTRLconst [int8(log32(^c))] x)
+(ANDLmodify [off] {sym} ptr (NOTL s:(SHLL (MOVLconst [1]) <t> x)) mem) =>
+	(BTRLmodify [off] {sym} ptr (ANDLconst <t> [31] x) mem)
+(ANDQmodify [off] {sym} ptr (NOTQ s:(SHLQ (MOVQconst [1]) <t> x)) mem) =>
+	(BTRQmodify [off] {sym} ptr (ANDQconst <t> [63] x) mem)
 
 // Special-case bit patterns on first/last bit.
 // generic.rules changes ANDs of high-part/low-part masks into a couple of shifts,
@@ -2050,11 +2062,15 @@
 ((ADD|SUB|MUL|DIV)SD x l:(MOVSDload [off] {sym} ptr mem)) && canMergeLoadClobber(v, l, x) && clobber(l) => ((ADD|SUB|MUL|DIV)SDload x [off] {sym} ptr mem)
 ((ADD|SUB|MUL|DIV)SS x l:(MOVSSload [off] {sym} ptr mem)) && canMergeLoadClobber(v, l, x) && clobber(l) => ((ADD|SUB|MUL|DIV)SSload x [off] {sym} ptr mem)
 (MOVLstore {sym} [off] ptr y:((ADD|AND|OR|XOR)Lload x [off] {sym} ptr mem) mem) && y.Uses==1 && clobber(y) => ((ADD|AND|OR|XOR)Lmodify [off] {sym} ptr x mem)
-(MOVLstore {sym} [off] ptr y:((ADD|SUB|AND|OR|XOR|BTC|BTR|BTS)L l:(MOVLload [off] {sym} ptr mem) x) mem) && y.Uses==1 && l.Uses==1 && clobber(y, l) =>
-	((ADD|SUB|AND|OR|XOR|BTC|BTR|BTS)Lmodify [off] {sym} ptr x mem)
+(MOVLstore {sym} [off] ptr y:((ADD|SUB|AND|OR|XOR)L l:(MOVLload [off] {sym} ptr mem) x) mem) && y.Uses==1 && l.Uses==1 && clobber(y, l) =>
+	((ADD|SUB|AND|OR|XOR)Lmodify [off] {sym} ptr x mem)
+(MOVLstore {sym} [off] ptr y:((BTC|BTR|BTS)L l:(MOVLload [off] {sym} ptr mem) <t> x) mem) && y.Uses==1 && l.Uses==1 && clobber(y, l) =>
+	((BTC|BTR|BTS)Lmodify [off] {sym} ptr (ANDLconst <t> [31] x) mem)
 (MOVQstore {sym} [off] ptr y:((ADD|AND|OR|XOR)Qload x [off] {sym} ptr mem) mem) && y.Uses==1 && clobber(y) => ((ADD|AND|OR|XOR)Qmodify [off] {sym} ptr x mem)
-(MOVQstore {sym} [off] ptr y:((ADD|SUB|AND|OR|XOR|BTC|BTR|BTS)Q l:(MOVQload [off] {sym} ptr mem) x) mem) && y.Uses==1 && l.Uses==1 && clobber(y, l) =>
-	((ADD|SUB|AND|OR|XOR|BTC|BTR|BTS)Qmodify [off] {sym} ptr x mem)
+(MOVQstore {sym} [off] ptr y:((ADD|SUB|AND|OR|XOR)Q l:(MOVQload [off] {sym} ptr mem) x) mem) && y.Uses==1 && l.Uses==1 && clobber(y, l) =>
+	((ADD|SUB|AND|OR|XOR)Qmodify [off] {sym} ptr x mem)
+(MOVQstore {sym} [off] ptr y:((BTC|BTR|BTS)Q l:(MOVQload [off] {sym} ptr mem) <t> x) mem) && y.Uses==1 && l.Uses==1 && clobber(y, l) =>
+	((BTC|BTR|BTS)Qmodify [off] {sym} ptr (ANDQconst <t> [63] x) mem)
 
 // Merge ADDQconst and LEAQ into atomic loads.
 (MOV(Q|L|B)atomicload [off1] {sym} (ADDQconst [off2] ptr) mem) && is32Bit(int64(off1)+int64(off2)) =>
diff --git a/src/cmd/compile/internal/ssa/gen/AMD64Ops.go b/src/cmd/compile/internal/ssa/gen/AMD64Ops.go
index de5372670b..a87581b68f 100644
--- a/src/cmd/compile/internal/ssa/gen/AMD64Ops.go
+++ b/src/cmd/compile/internal/ssa/gen/AMD64Ops.go
@@ -358,6 +358,11 @@ func init() {
 		{name: "BTSQconst", argLength: 1, reg: gp11, asm: "BTSQ", resultInArg0: true, clobberFlags: true, aux: "Int8"}, // set bit auxint in arg0, 0 <= auxint < 64
 
 		// direct bit operation on memory operand
+		//
+		// Note that these operations do not mask the bit offset (arg1), and will write beyond their expected
+		// bounds if that argument is larger than 64/32 (for BT*Q and BT*L, respectively). If the compiler
+		// cannot prove that arg1 is in range, it must be explicitly masked (see e.g. the patterns that produce
+		// BT*modify from (MOVstore (BT* (MOVLload ptr mem) x) mem)).
 		{name: "BTCQmodify", argLength: 3, reg: gpstore, asm: "BTCQ", aux: "SymOff", typ: "Mem", clobberFlags: true, faultOnNilArg0: true, symEffect: "Read,Write"},     // complement bit arg1 in 64-bit arg0+auxint+aux, arg2=mem
 		{name: "BTCLmodify", argLength: 3, reg: gpstore, asm: "BTCL", aux: "SymOff", typ: "Mem", clobberFlags: true, faultOnNilArg0: true, symEffect: "Read,Write"},     // complement bit arg1 in 32-bit arg0+auxint+aux, arg2=mem
 		{name: "BTSQmodify", argLength: 3, reg: gpstore, asm: "BTSQ", aux: "SymOff", typ: "Mem", clobberFlags: true, faultOnNilArg0: true, symEffect: "Read,Write"},     // set bit arg1 in 64-bit arg0+auxint+aux, arg2=mem
diff --git a/src/cmd/compile/internal/ssa/rewriteAMD64.go b/src/cmd/compile/internal/ssa/rewriteAMD64.go
index 75d4ff7357..8272a406d9 100644
--- a/src/cmd/compile/internal/ssa/rewriteAMD64.go
+++ b/src/cmd/compile/internal/ssa/rewriteAMD64.go
@@ -2998,6 +2998,36 @@ func rewriteValueAMD64_OpAMD64ANDLmodify(v *Value) bool {
 	v_2 := v.Args[2]
 	v_1 := v.Args[1]
 	v_0 := v.Args[0]
+	b := v.Block
+	// match: (ANDLmodify [off] {sym} ptr (NOTL s:(SHLL (MOVLconst [1]) <t> x)) mem)
+	// result: (BTRLmodify [off] {sym} ptr (ANDLconst <t> [31] x) mem)
+	for {
+		off := auxIntToInt32(v.AuxInt)
+		sym := auxToSym(v.Aux)
+		ptr := v_0
+		if v_1.Op != OpAMD64NOTL {
+			break
+		}
+		s := v_1.Args[0]
+		if s.Op != OpAMD64SHLL {
+			break
+		}
+		t := s.Type
+		x := s.Args[1]
+		s_0 := s.Args[0]
+		if s_0.Op != OpAMD64MOVLconst || auxIntToInt32(s_0.AuxInt) != 1 {
+			break
+		}
+		mem := v_2
+		v.reset(OpAMD64BTRLmodify)
+		v.AuxInt = int32ToAuxInt(off)
+		v.Aux = symToAux(sym)
+		v0 := b.NewValue0(v.Pos, OpAMD64ANDLconst, t)
+		v0.AuxInt = int32ToAuxInt(31)
+		v0.AddArg(x)
+		v.AddArg3(ptr, v0, mem)
+		return true
+	}
 	// match: (ANDLmodify [off1] {sym} (ADDQconst [off2] base) val mem)
 	// cond: is32Bit(int64(off1)+int64(off2))
 	// result: (ANDLmodify [off1+off2] {sym} base val mem)
@@ -3377,6 +3407,36 @@ func rewriteValueAMD64_OpAMD64ANDQmodify(v *Value) bool {
 	v_2 := v.Args[2]
 	v_1 := v.Args[1]
 	v_0 := v.Args[0]
+	b := v.Block
+	// match: (ANDQmodify [off] {sym} ptr (NOTQ s:(SHLQ (MOVQconst [1]) <t> x)) mem)
+	// result: (BTRQmodify [off] {sym} ptr (ANDQconst <t> [63] x) mem)
+	for {
+		off := auxIntToInt32(v.AuxInt)
+		sym := auxToSym(v.Aux)
+		ptr := v_0
+		if v_1.Op != OpAMD64NOTQ {
+			break
+		}
+		s := v_1.Args[0]
+		if s.Op != OpAMD64SHLQ {
+			break
+		}
+		t := s.Type
+		x := s.Args[1]
+		s_0 := s.Args[0]
+		if s_0.Op != OpAMD64MOVQconst || auxIntToInt64(s_0.AuxInt) != 1 {
+			break
+		}
+		mem := v_2
+		v.reset(OpAMD64BTRQmodify)
+		v.AuxInt = int32ToAuxInt(off)
+		v.Aux = symToAux(sym)
+		v0 := b.NewValue0(v.Pos, OpAMD64ANDQconst, t)
+		v0.AuxInt = int32ToAuxInt(63)
+		v0.AddArg(x)
+		v.AddArg3(ptr, v0, mem)
+		return true
+	}
 	// match: (ANDQmodify [off1] {sym} (ADDQconst [off2] base) val mem)
 	// cond: is32Bit(int64(off1)+int64(off2))
 	// result: (ANDQmodify [off1+off2] {sym} base val mem)
@@ -12709,9 +12769,9 @@ func rewriteValueAMD64_OpAMD64MOVLstore(v *Value) bool {
 		}
 		break
 	}
-	// match: (MOVLstore {sym} [off] ptr y:(BTCL l:(MOVLload [off] {sym} ptr mem) x) mem)
+	// match: (MOVLstore {sym} [off] ptr y:(BTCL l:(MOVLload [off] {sym} ptr mem) <t> x) mem)
 	// cond: y.Uses==1 && l.Uses==1 && clobber(y, l)
-	// result: (BTCLmodify [off] {sym} ptr x mem)
+	// result: (BTCLmodify [off] {sym} ptr (ANDLconst <t> [31] x) mem)
 	for {
 		off := auxIntToInt32(v.AuxInt)
 		sym := auxToSym(v.Aux)
@@ -12720,6 +12780,7 @@ func rewriteValueAMD64_OpAMD64MOVLstore(v *Value) bool {
 		if y.Op != OpAMD64BTCL {
 			break
 		}
+		t := y.Type
 		x := y.Args[1]
 		l := y.Args[0]
 		if l.Op != OpAMD64MOVLload || auxIntToInt32(l.AuxInt) != off || auxToSym(l.Aux) != sym {
@@ -12732,12 +12793,15 @@ func rewriteValueAMD64_OpAMD64MOVLstore(v *Value) bool {
 		v.reset(OpAMD64BTCLmodify)
 		v.AuxInt = int32ToAuxInt(off)
 		v.Aux = symToAux(sym)
-		v.AddArg3(ptr, x, mem)
+		v0 := b.NewValue0(l.Pos, OpAMD64ANDLconst, t)
+		v0.AuxInt = int32ToAuxInt(31)
+		v0.AddArg(x)
+		v.AddArg3(ptr, v0, mem)
 		return true
 	}
-	// match: (MOVLstore {sym} [off] ptr y:(BTRL l:(MOVLload [off] {sym} ptr mem) x) mem)
+	// match: (MOVLstore {sym} [off] ptr y:(BTRL l:(MOVLload [off] {sym} ptr mem) <t> x) mem)
 	// cond: y.Uses==1 && l.Uses==1 && clobber(y, l)
-	// result: (BTRLmodify [off] {sym} ptr x mem)
+	// result: (BTRLmodify [off] {sym} ptr (ANDLconst <t> [31] x) mem)
 	for {
 		off := auxIntToInt32(v.AuxInt)
 		sym := auxToSym(v.Aux)
@@ -12746,6 +12810,7 @@ func rewriteValueAMD64_OpAMD64MOVLstore(v *Value) bool {
 		if y.Op != OpAMD64BTRL {
 			break
 		}
+		t := y.Type
 		x := y.Args[1]
 		l := y.Args[0]
 		if l.Op != OpAMD64MOVLload || auxIntToInt32(l.AuxInt) != off || auxToSym(l.Aux) != sym {
@@ -12758,12 +12823,15 @@ func rewriteValueAMD64_OpAMD64MOVLstore(v *Value) bool {
 		v.reset(OpAMD64BTRLmodify)
 		v.AuxInt = int32ToAuxInt(off)
 		v.Aux = symToAux(sym)
-		v.AddArg3(ptr, x, mem)
+		v0 := b.NewValue0(l.Pos, OpAMD64ANDLconst, t)
+		v0.AuxInt = int32ToAuxInt(31)
+		v0.AddArg(x)
+		v.AddArg3(ptr, v0, mem)
 		return true
 	}
-	// match: (MOVLstore {sym} [off] ptr y:(BTSL l:(MOVLload [off] {sym} ptr mem) x) mem)
+	// match: (MOVLstore {sym} [off] ptr y:(BTSL l:(MOVLload [off] {sym} ptr mem) <t> x) mem)
 	// cond: y.Uses==1 && l.Uses==1 && clobber(y, l)
-	// result: (BTSLmodify [off] {sym} ptr x mem)
+	// result: (BTSLmodify [off] {sym} ptr (ANDLconst <t> [31] x) mem)
 	for {
 		off := auxIntToInt32(v.AuxInt)
 		sym := auxToSym(v.Aux)
@@ -12772,6 +12840,7 @@ func rewriteValueAMD64_OpAMD64MOVLstore(v *Value) bool {
 		if y.Op != OpAMD64BTSL {
 			break
 		}
+		t := y.Type
 		x := y.Args[1]
 		l := y.Args[0]
 		if l.Op != OpAMD64MOVLload || auxIntToInt32(l.AuxInt) != off || auxToSym(l.Aux) != sym {
@@ -12784,7 +12853,10 @@ func rewriteValueAMD64_OpAMD64MOVLstore(v *Value) bool {
 		v.reset(OpAMD64BTSLmodify)
 		v.AuxInt = int32ToAuxInt(off)
 		v.Aux = symToAux(sym)
-		v.AddArg3(ptr, x, mem)
+		v0 := b.NewValue0(l.Pos, OpAMD64ANDLconst, t)
+		v0.AuxInt = int32ToAuxInt(31)
+		v0.AddArg(x)
+		v.AddArg3(ptr, v0, mem)
 		return true
 	}
 	// match: (MOVLstore [off] {sym} ptr a:(ADDLconst [c] l:(MOVLload [off] {sym} ptr2 mem)) mem)
@@ -13525,6 +13597,7 @@ func rewriteValueAMD64_OpAMD64MOVQstore(v *Value) bool {
 	v_2 := v.Args[2]
 	v_1 := v.Args[1]
 	v_0 := v.Args[0]
+	b := v.Block
 	// match: (MOVQstore [off1] {sym} (ADDQconst [off2] ptr) val mem)
 	// cond: is32Bit(int64(off1)+int64(off2))
 	// result: (MOVQstore [off1+off2] {sym} ptr val mem)
@@ -13890,9 +13963,9 @@ func rewriteValueAMD64_OpAMD64MOVQstore(v *Value) bool {
 		}
 		break
 	}
-	// match: (MOVQstore {sym} [off] ptr y:(BTCQ l:(MOVQload [off] {sym} ptr mem) x) mem)
+	// match: (MOVQstore {sym} [off] ptr y:(BTCQ l:(MOVQload [off] {sym} ptr mem) <t> x) mem)
 	// cond: y.Uses==1 && l.Uses==1 && clobber(y, l)
-	// result: (BTCQmodify [off] {sym} ptr x mem)
+	// result: (BTCQmodify [off] {sym} ptr (ANDQconst <t> [63] x) mem)
 	for {
 		off := auxIntToInt32(v.AuxInt)
 		sym := auxToSym(v.Aux)
@@ -13901,6 +13974,7 @@ func rewriteValueAMD64_OpAMD64MOVQstore(v *Value) bool {
 		if y.Op != OpAMD64BTCQ {
 			break
 		}
+		t := y.Type
 		x := y.Args[1]
 		l := y.Args[0]
 		if l.Op != OpAMD64MOVQload || auxIntToInt32(l.AuxInt) != off || auxToSym(l.Aux) != sym {
@@ -13913,12 +13987,15 @@ func rewriteValueAMD64_OpAMD64MOVQstore(v *Value) bool {
 		v.reset(OpAMD64BTCQmodify)
 		v.AuxInt = int32ToAuxInt(off)
 		v.Aux = symToAux(sym)
-		v.AddArg3(ptr, x, mem)
+		v0 := b.NewValue0(l.Pos, OpAMD64ANDQconst, t)
+		v0.AuxInt = int32ToAuxInt(63)
+		v0.AddArg(x)
+		v.AddArg3(ptr, v0, mem)
 		return true
 	}
-	// match: (MOVQstore {sym} [off] ptr y:(BTRQ l:(MOVQload [off] {sym} ptr mem) x) mem)
+	// match: (MOVQstore {sym} [off] ptr y:(BTRQ l:(MOVQload [off] {sym} ptr mem) <t> x) mem)
 	// cond: y.Uses==1 && l.Uses==1 && clobber(y, l)
-	// result: (BTRQmodify [off] {sym} ptr x mem)
+	// result: (BTRQmodify [off] {sym} ptr (ANDQconst <t> [63] x) mem)
 	for {
 		off := auxIntToInt32(v.AuxInt)
 		sym := auxToSym(v.Aux)
@@ -13927,6 +14004,7 @@ func rewriteValueAMD64_OpAMD64MOVQstore(v *Value) bool {
 		if y.Op != OpAMD64BTRQ {
 			break
 		}
+		t := y.Type
 		x := y.Args[1]
 		l := y.Args[0]
 		if l.Op != OpAMD64MOVQload || auxIntToInt32(l.AuxInt) != off || auxToSym(l.Aux) != sym {
@@ -13939,12 +14017,15 @@ func rewriteValueAMD64_OpAMD64MOVQstore(v *Value) bool {
 		v.reset(OpAMD64BTRQmodify)
 		v.AuxInt = int32ToAuxInt(off)
 		v.Aux = symToAux(sym)
-		v.AddArg3(ptr, x, mem)
+		v0 := b.NewValue0(l.Pos, OpAMD64ANDQconst, t)
+		v0.AuxInt = int32ToAuxInt(63)
+		v0.AddArg(x)
+		v.AddArg3(ptr, v0, mem)
 		return true
 	}
-	// match: (MOVQstore {sym} [off] ptr y:(BTSQ l:(MOVQload [off] {sym} ptr mem) x) mem)
+	// match: (MOVQstore {sym} [off] ptr y:(BTSQ l:(MOVQload [off] {sym} ptr mem) <t> x) mem)
 	// cond: y.Uses==1 && l.Uses==1 && clobber(y, l)
-	// result: (BTSQmodify [off] {sym} ptr x mem)
+	// result: (BTSQmodify [off] {sym} ptr (ANDQconst <t> [63] x) mem)
 	for {
 		off := auxIntToInt32(v.AuxInt)
 		sym := auxToSym(v.Aux)
@@ -13953,6 +14034,7 @@ func rewriteValueAMD64_OpAMD64MOVQstore(v *Value) bool {
 		if y.Op != OpAMD64BTSQ {
 			break
 		}
+		t := y.Type
 		x := y.Args[1]
 		l := y.Args[0]
 		if l.Op != OpAMD64MOVQload || auxIntToInt32(l.AuxInt) != off || auxToSym(l.Aux) != sym {
@@ -13965,7 +14047,10 @@ func rewriteValueAMD64_OpAMD64MOVQstore(v *Value) bool {
 		v.reset(OpAMD64BTSQmodify)
 		v.AuxInt = int32ToAuxInt(off)
 		v.Aux = symToAux(sym)
-		v.AddArg3(ptr, x, mem)
+		v0 := b.NewValue0(l.Pos, OpAMD64ANDQconst, t)
+		v0.AuxInt = int32ToAuxInt(63)
+		v0.AddArg(x)
+		v.AddArg3(ptr, v0, mem)
 		return true
 	}
 	// match: (MOVQstore [off] {sym} ptr a:(ADDQconst [c] l:(MOVQload [off] {sym} ptr2 mem)) mem)
@@ -18352,6 +18437,33 @@ func rewriteValueAMD64_OpAMD64ORLmodify(v *Value) bool {
 	v_2 := v.Args[2]
 	v_1 := v.Args[1]
 	v_0 := v.Args[0]
+	b := v.Block
+	// match: (ORLmodify [off] {sym} ptr s:(SHLL (MOVLconst [1]) <t> x) mem)
+	// result: (BTSLmodify [off] {sym} ptr (ANDLconst <t> [31] x) mem)
+	for {
+		off := auxIntToInt32(v.AuxInt)
+		sym := auxToSym(v.Aux)
+		ptr := v_0
+		s := v_1
+		if s.Op != OpAMD64SHLL {
+			break
+		}
+		t := s.Type
+		x := s.Args[1]
+		s_0 := s.Args[0]
+		if s_0.Op != OpAMD64MOVLconst || auxIntToInt32(s_0.AuxInt) != 1 {
+			break
+		}
+		mem := v_2
+		v.reset(OpAMD64BTSLmodify)
+		v.AuxInt = int32ToAuxInt(off)
+		v.Aux = symToAux(sym)
+		v0 := b.NewValue0(v.Pos, OpAMD64ANDLconst, t)
+		v0.AuxInt = int32ToAuxInt(31)
+		v0.AddArg(x)
+		v.AddArg3(ptr, v0, mem)
+		return true
+	}
 	// match: (ORLmodify [off1] {sym} (ADDQconst [off2] base) val mem)
 	// cond: is32Bit(int64(off1)+int64(off2))
 	// result: (ORLmodify [off1+off2] {sym} base val mem)
@@ -19979,6 +20091,33 @@ func rewriteValueAMD64_OpAMD64ORQmodify(v *Value) bool {
 	v_2 := v.Args[2]
 	v_1 := v.Args[1]
 	v_0 := v.Args[0]
+	b := v.Block
+	// match: (ORQmodify [off] {sym} ptr s:(SHLQ (MOVQconst [1]) <t> x) mem)
+	// result: (BTSQmodify [off] {sym} ptr (ANDQconst <t> [63] x) mem)
+	for {
+		off := auxIntToInt32(v.AuxInt)
+		sym := auxToSym(v.Aux)
+		ptr := v_0
+		s := v_1
+		if s.Op != OpAMD64SHLQ {
+			break
+		}
+		t := s.Type
+		x := s.Args[1]
+		s_0 := s.Args[0]
+		if s_0.Op != OpAMD64MOVQconst || auxIntToInt64(s_0.AuxInt) != 1 {
+			break
+		}
+		mem := v_2
+		v.reset(OpAMD64BTSQmodify)
+		v.AuxInt = int32ToAuxInt(off)
+		v.Aux = symToAux(sym)
+		v0 := b.NewValue0(v.Pos, OpAMD64ANDQconst, t)
+		v0.AuxInt = int32ToAuxInt(63)
+		v0.AddArg(x)
+		v.AddArg3(ptr, v0, mem)
+		return true
+	}
 	// match: (ORQmodify [off1] {sym} (ADDQconst [off2] base) val mem)
 	// cond: is32Bit(int64(off1)+int64(off2))
 	// result: (ORQmodify [off1+off2] {sym} base val mem)
@@ -28014,6 +28153,33 @@ func rewriteValueAMD64_OpAMD64XORLmodify(v *Value) bool {
 	v_2 := v.Args[2]
 	v_1 := v.Args[1]
 	v_0 := v.Args[0]
+	b := v.Block
+	// match: (XORLmodify [off] {sym} ptr s:(SHLL (MOVLconst [1]) <t> x) mem)
+	// result: (BTCLmodify [off] {sym} ptr (ANDLconst <t> [31] x) mem)
+	for {
+		off := auxIntToInt32(v.AuxInt)
+		sym := auxToSym(v.Aux)
+		ptr := v_0
+		s := v_1
+		if s.Op != OpAMD64SHLL {
+			break
+		}
+		t := s.Type
+		x := s.Args[1]
+		s_0 := s.Args[0]
+		if s_0.Op != OpAMD64MOVLconst || auxIntToInt32(s_0.AuxInt) != 1 {
+			break
+		}
+		mem := v_2
+		v.reset(OpAMD64BTCLmodify)
+		v.AuxInt = int32ToAuxInt(off)
+		v.Aux = symToAux(sym)
+		v0 := b.NewValue0(v.Pos, OpAMD64ANDLconst, t)
+		v0.AuxInt = int32ToAuxInt(31)
+		v0.AddArg(x)
+		v.AddArg3(ptr, v0, mem)
+		return true
+	}
 	// match: (XORLmodify [off1] {sym} (ADDQconst [off2] base) val mem)
 	// cond: is32Bit(int64(off1)+int64(off2))
 	// result: (XORLmodify [off1+off2] {sym} base val mem)
@@ -28382,6 +28548,33 @@ func rewriteValueAMD64_OpAMD64XORQmodify(v *Value) bool {
 	v_2 := v.Args[2]
 	v_1 := v.Args[1]
 	v_0 := v.Args[0]
+	b := v.Block
+	// match: (XORQmodify [off] {sym} ptr s:(SHLQ (MOVQconst [1]) <t> x) mem)
+	// result: (BTCQmodify [off] {sym} ptr (ANDQconst <t> [63] x) mem)
+	for {
+		off := auxIntToInt32(v.AuxInt)
+		sym := auxToSym(v.Aux)
+		ptr := v_0
+		s := v_1
+		if s.Op != OpAMD64SHLQ {
+			break
+		}
+		t := s.Type
+		x := s.Args[1]
+		s_0 := s.Args[0]
+		if s_0.Op != OpAMD64MOVQconst || auxIntToInt64(s_0.AuxInt) != 1 {
+			break
+		}
+		mem := v_2
+		v.reset(OpAMD64BTCQmodify)
+		v.AuxInt = int32ToAuxInt(off)
+		v.Aux = symToAux(sym)
+		v0 := b.NewValue0(v.Pos, OpAMD64ANDQconst, t)
+		v0.AuxInt = int32ToAuxInt(63)
+		v0.AddArg(x)
+		v.AddArg3(ptr, v0, mem)
+		return true
+	}
 	// match: (XORQmodify [off1] {sym} (ADDQconst [off2] base) val mem)
 	// cond: is32Bit(int64(off1)+int64(off2))
 	// result: (XORQmodify [off1+off2] {sym} base val mem)
diff --git a/src/cmd/compile/internal/ssa/shortcircuit.go b/src/cmd/compile/internal/ssa/shortcircuit.go
index 7b4ee2e81c..4dd86ec74f 100644
--- a/src/cmd/compile/internal/ssa/shortcircuit.go
+++ b/src/cmd/compile/internal/ssa/shortcircuit.go
@@ -138,6 +138,24 @@ func shortcircuitBlock(b *Block) bool {
 	if len(b.Values) != nval+nOtherPhi {
 		return false
 	}
+	if nOtherPhi > 0 {
+		// Check for any phi which is the argument of another phi.
+		// These cases are tricky, as substitutions done by replaceUses
+		// are no longer trivial to do in any ordering. See issue 45175.
+		m := make(map[*Value]bool, 1+nOtherPhi)
+		for _, v := range b.Values {
+			if v.Op == OpPhi {
+				m[v] = true
+			}
+		}
+		for v := range m {
+			for _, a := range v.Args {
+				if a != v && m[a] {
+					return false
+				}
+			}
+		}
+	}
 
 	// Locate index of first const phi arg.
 	cidx := -1
diff --git a/src/cmd/go.mod b/src/cmd/go.mod
index 35582f3975..70b1b0690b 100644
--- a/src/cmd/go.mod
+++ b/src/cmd/go.mod
@@ -6,7 +6,7 @@ require (
 	github.com/google/pprof v0.0.0-20201203190320-1bf35d6f28c2
 	golang.org/x/arch v0.0.0-20201008161808-52c3e6f60cff
 	golang.org/x/crypto v0.0.0-20201016220609-9e8e0b390897
-	golang.org/x/mod v0.4.2-0.20210302225053-d515b24adc21
+	golang.org/x/mod v0.4.2-0.20210325185522-dbbbf8a3c6ea
 	golang.org/x/sys v0.0.0-20201204225414-ed752295db88 // indirect
 	golang.org/x/tools v0.0.0-20210107193943-4ed967dd8eff
 )
diff --git a/src/cmd/go.sum b/src/cmd/go.sum
index 10340d441f..edda18b526 100644
--- a/src/cmd/go.sum
+++ b/src/cmd/go.sum
@@ -14,8 +14,8 @@ golang.org/x/crypto v0.0.0-20200622213623-75b288015ac9/go.mod h1:LzIPMQfyMNhhGPh
 golang.org/x/crypto v0.0.0-20201016220609-9e8e0b390897 h1:pLI5jrR7OSLijeIDcmRxNmw2api+jEfxLoykJVice/E=
 golang.org/x/crypto v0.0.0-20201016220609-9e8e0b390897/go.mod h1:LzIPMQfyMNhhGPhUkYOs5KpL4U8rLKemX1yGLhDgUto=
 golang.org/x/mod v0.3.0/go.mod h1:s0Qsj1ACt9ePp/hMypM3fl4fZqREWJwdYDEqhRiZZUA=
-golang.org/x/mod v0.4.2-0.20210302225053-d515b24adc21 h1:FnWKa8BJXkVQ+16E52jkfBOJPx2cG8y/6X376nOgSM4=
-golang.org/x/mod v0.4.2-0.20210302225053-d515b24adc21/go.mod h1:s0Qsj1ACt9ePp/hMypM3fl4fZqREWJwdYDEqhRiZZUA=
+golang.org/x/mod v0.4.2-0.20210325185522-dbbbf8a3c6ea h1:zAn46O7Vmm6KdLXx+635hPZSArrt/wNctv4Ab70Jw3k=
+golang.org/x/mod v0.4.2-0.20210325185522-dbbbf8a3c6ea/go.mod h1:s0Qsj1ACt9ePp/hMypM3fl4fZqREWJwdYDEqhRiZZUA=
 golang.org/x/net v0.0.0-20190404232315-eb5bcb51f2a3/go.mod h1:t9HGtf8HONx5eT2rtn7q6eTqICYqUVnKs3thJo3Qplg=
 golang.org/x/net v0.0.0-20190620200207-3b0461eec859/go.mod h1:z5CRVTTTmAJ677TzLLGU+0bjPO0LkuOLi4/5GtJWs/s=
 golang.org/x/net v0.0.0-20201021035429-f5854403a974/go.mod h1:sp8m0HH+o8qH0wwXwYZr8TS3Oi6o0r6Gce1SSxlDquU=
diff --git a/src/cmd/go/alldocs.go b/src/cmd/go/alldocs.go
index e7c63f0749..84f89c9d2d 100644
--- a/src/cmd/go/alldocs.go
+++ b/src/cmd/go/alldocs.go
@@ -692,18 +692,22 @@
 // arguments must satisfy the following constraints:
 //
 // - Arguments must be package paths or package patterns (with "..." wildcards).
-//   They must not be standard packages (like fmt), meta-patterns (std, cmd,
-//   all), or relative or absolute file paths.
+// They must not be standard packages (like fmt), meta-patterns (std, cmd,
+// all), or relative or absolute file paths.
+//
 // - All arguments must have the same version suffix. Different queries are not
-//   allowed, even if they refer to the same version.
+// allowed, even if they refer to the same version.
+//
 // - All arguments must refer to packages in the same module at the same version.
+//
 // - No module is considered the "main" module. If the module containing
-//   packages named on the command line has a go.mod file, it must not contain
-//   directives (replace and exclude) that would cause it to be interpreted
-//   differently than if it were the main module. The module must not require
-//   a higher version of itself.
+// packages named on the command line has a go.mod file, it must not contain
+// directives (replace and exclude) that would cause it to be interpreted
+// differently than if it were the main module. The module must not require
+// a higher version of itself.
+//
 // - Package path arguments must refer to main packages. Pattern arguments
-//   will only match main packages.
+// will only match main packages.
 //
 // If the arguments don't have version suffixes, "go install" may run in
 // module-aware mode or GOPATH mode, depending on the GO111MODULE environment
diff --git a/src/cmd/go/internal/modfetch/cache.go b/src/cmd/go/internal/modfetch/cache.go
index 3a2ff63721..07e046c8cb 100644
--- a/src/cmd/go/internal/modfetch/cache.go
+++ b/src/cmd/go/internal/modfetch/cache.go
@@ -84,6 +84,7 @@ func DownloadDir(m module.Version) (string, error) {
 		return "", err
 	}
 
+	// Check whether the directory itself exists.
 	dir := filepath.Join(cfg.GOMODCACHE, enc+"@"+encVer)
 	if fi, err := os.Stat(dir); os.IsNotExist(err) {
 		return dir, err
@@ -92,6 +93,9 @@ func DownloadDir(m module.Version) (string, error) {
 	} else if !fi.IsDir() {
 		return dir, &DownloadDirPartialError{dir, errors.New("not a directory")}
 	}
+
+	// Check if a .partial file exists. This is created at the beginning of
+	// a download and removed after the zip is extracted.
 	partialPath, err := CachePath(m, "partial")
 	if err != nil {
 		return dir, err
@@ -101,6 +105,19 @@ func DownloadDir(m module.Version) (string, error) {
 	} else if !os.IsNotExist(err) {
 		return dir, err
 	}
+
+	// Check if a .ziphash file exists. It should be created before the
+	// zip is extracted, but if it was deleted (by another program?), we need
+	// to re-calculate it.
+	ziphashPath, err := CachePath(m, "ziphash")
+	if err != nil {
+		return dir, err
+	}
+	if _, err := os.Stat(ziphashPath); os.IsNotExist(err) {
+		return dir, &DownloadDirPartialError{dir, errors.New("ziphash file is missing")}
+	} else if err != nil {
+		return dir, err
+	}
 	return dir, nil
 }
 
diff --git a/src/cmd/go/internal/modfetch/fetch.go b/src/cmd/go/internal/modfetch/fetch.go
index c55c3cf253..eb7d30e0ab 100644
--- a/src/cmd/go/internal/modfetch/fetch.go
+++ b/src/cmd/go/internal/modfetch/fetch.go
@@ -170,13 +170,16 @@ func DownloadZip(ctx context.Context, mod module.Version) (zipfile string, err e
 		if err != nil {
 			return cached{"", err}
 		}
+		ziphashfile := zipfile + "hash"
 
-		// Skip locking if the zipfile already exists.
+		// Return without locking if the zip and ziphash files exist.
 		if _, err := os.Stat(zipfile); err == nil {
-			return cached{zipfile, nil}
+			if _, err := os.Stat(ziphashfile); err == nil {
+				return cached{zipfile, nil}
+			}
 		}
 
-		// The zip file does not exist. Acquire the lock and create it.
+		// The zip or ziphash file does not exist. Acquire the lock and create them.
 		if cfg.CmdName != "mod download" {
 			fmt.Fprintf(os.Stderr, "go: downloading %s %s\n", mod.Path, mod.Version)
 		}
@@ -186,14 +189,6 @@ func DownloadZip(ctx context.Context, mod module.Version) (zipfile string, err e
 		}
 		defer unlock()
 
-		// Double-check that the zipfile was not created while we were waiting for
-		// the lock.
-		if _, err := os.Stat(zipfile); err == nil {
-			return cached{zipfile, nil}
-		}
-		if err := os.MkdirAll(filepath.Dir(zipfile), 0777); err != nil {
-			return cached{"", err}
-		}
 		if err := downloadZip(ctx, mod, zipfile); err != nil {
 			return cached{"", err}
 		}
@@ -206,6 +201,25 @@ func downloadZip(ctx context.Context, mod module.Version, zipfile string) (err e
 	ctx, span := trace.StartSpan(ctx, "modfetch.downloadZip "+zipfile)
 	defer span.Done()
 
+	// Double-check that the zipfile was not created while we were waiting for
+	// the lock in DownloadZip.
+	ziphashfile := zipfile + "hash"
+	var zipExists, ziphashExists bool
+	if _, err := os.Stat(zipfile); err == nil {
+		zipExists = true
+	}
+	if _, err := os.Stat(ziphashfile); err == nil {
+		ziphashExists = true
+	}
+	if zipExists && ziphashExists {
+		return nil
+	}
+
+	// Create parent directories.
+	if err := os.MkdirAll(filepath.Dir(zipfile), 0777); err != nil {
+		return err
+	}
+
 	// Clean up any remaining tempfiles from previous runs.
 	// This is only safe to do because the lock file ensures that their
 	// writers are no longer active.
@@ -217,6 +231,12 @@ func downloadZip(ctx context.Context, mod module.Version, zipfile string) (err e
 		}
 	}
 
+	// If the zip file exists, the ziphash file must have been deleted
+	// or lost after a file system crash. Re-hash the zip without downloading.
+	if zipExists {
+		return hashZip(mod, zipfile, ziphashfile)
+	}
+
 	// From here to the os.Rename call below is functionally almost equivalent to
 	// renameio.WriteToFile, with one key difference: we want to validate the
 	// contents of the file (by hashing it) before we commit it. Because the file
@@ -289,15 +309,7 @@ func downloadZip(ctx context.Context, mod module.Version, zipfile string) (err e
 	}
 
 	// Hash the zip file and check the sum before renaming to the final location.
-	hash, err := dirhash.HashZip(f.Name(), dirhash.DefaultHash)
-	if err != nil {
-		return err
-	}
-	if err := checkModSum(mod, hash); err != nil {
-		return err
-	}
-
-	if err := renameio.WriteFile(zipfile+"hash", []byte(hash), 0666); err != nil {
+	if err := hashZip(mod, f.Name(), ziphashfile); err != nil {
 		return err
 	}
 	if err := os.Rename(f.Name(), zipfile); err != nil {
@@ -309,6 +321,22 @@ func downloadZip(ctx context.Context, mod module.Version, zipfile string) (err e
 	return nil
 }
 
+// hashZip reads the zip file opened in f, then writes the hash to ziphashfile,
+// overwriting that file if it exists.
+//
+// If the hash does not match go.sum (or the sumdb if enabled), hashZip returns
+// an error and does not write ziphashfile.
+func hashZip(mod module.Version, zipfile, ziphashfile string) error {
+	hash, err := dirhash.HashZip(zipfile, dirhash.DefaultHash)
+	if err != nil {
+		return err
+	}
+	if err := checkModSum(mod, hash); err != nil {
+		return err
+	}
+	return renameio.WriteFile(ziphashfile, []byte(hash), 0666)
+}
+
 // makeDirsReadOnly makes a best-effort attempt to remove write permissions for dir
 // and its transitive contents.
 func makeDirsReadOnly(dir string) {
@@ -452,11 +480,6 @@ func HaveSum(mod module.Version) bool {
 
 // checkMod checks the given module's checksum.
 func checkMod(mod module.Version) {
-	if cfg.GOMODCACHE == "" {
-		// Do not use current directory.
-		return
-	}
-
 	// Do the file I/O before acquiring the go.sum lock.
 	ziphash, err := CachePath(mod, "ziphash")
 	if err != nil {
@@ -464,10 +487,6 @@ func checkMod(mod module.Version) {
 	}
 	data, err := renameio.ReadFile(ziphash)
 	if err != nil {
-		if errors.Is(err, fs.ErrNotExist) {
-			// This can happen if someone does rm -rf GOPATH/src/cache/download. So it goes.
-			return
-		}
 		base.Fatalf("verifying %v", module.VersionError(mod, err))
 	}
 	h := strings.TrimSpace(string(data))
diff --git a/src/cmd/go/internal/work/build.go b/src/cmd/go/internal/work/build.go
index 780d639c5d..f024b07b22 100644
--- a/src/cmd/go/internal/work/build.go
+++ b/src/cmd/go/internal/work/build.go
@@ -482,18 +482,22 @@ To eliminate ambiguity about which module versions are used in the build, the
 arguments must satisfy the following constraints:
 
 - Arguments must be package paths or package patterns (with "..." wildcards).
-  They must not be standard packages (like fmt), meta-patterns (std, cmd,
-  all), or relative or absolute file paths.
+They must not be standard packages (like fmt), meta-patterns (std, cmd,
+all), or relative or absolute file paths.
+
 - All arguments must have the same version suffix. Different queries are not
-  allowed, even if they refer to the same version.
+allowed, even if they refer to the same version.
+
 - All arguments must refer to packages in the same module at the same version.
+
 - No module is considered the "main" module. If the module containing
-  packages named on the command line has a go.mod file, it must not contain
-  directives (replace and exclude) that would cause it to be interpreted
-  differently than if it were the main module. The module must not require
-  a higher version of itself.
+packages named on the command line has a go.mod file, it must not contain
+directives (replace and exclude) that would cause it to be interpreted
+differently than if it were the main module. The module must not require
+a higher version of itself.
+
 - Package path arguments must refer to main packages. Pattern arguments
-  will only match main packages.
+will only match main packages.
 
 If the arguments don't have version suffixes, "go install" may run in
 module-aware mode or GOPATH mode, depending on the GO111MODULE environment
diff --git a/src/cmd/go/testdata/script/mod_get_missing_ziphash.txt b/src/cmd/go/testdata/script/mod_get_missing_ziphash.txt
new file mode 100644
index 0000000000..8f6793edf5
--- /dev/null
+++ b/src/cmd/go/testdata/script/mod_get_missing_ziphash.txt
@@ -0,0 +1,55 @@
+# Test that if the module cache contains an extracted source directory but not
+# a ziphash, 'go build' complains about a missing sum, and 'go get' adds
+# the sum. Verifies #44749.
+
+# With a tidy go.sum, go build succeeds. This also populates the module cache.
+cp go.sum.tidy go.sum
+go build -n use
+env GOPROXY=off
+env GOSUMDB=off
+
+# Control case: if we delete the hash for rsc.io/quote v1.5.2,
+# 'go build' reports an error. 'go get' adds the sum.
+cp go.sum.bug go.sum
+! go build -n use
+stderr '^use.go:3:8: missing go.sum entry for module providing package rsc.io/quote \(imported by use\); to add:\n\tgo get use$'
+go get -d use
+cmp go.sum go.sum.tidy
+go build -n use
+
+# If we delete the hash *and* the ziphash file, we should see the same behavior.
+cp go.sum.bug go.sum
+rm $WORK/gopath/pkg/mod/cache/download/rsc.io/quote/@v/v1.5.2.ziphash
+! go build -n use
+stderr '^use.go:3:8: missing go.sum entry for module providing package rsc.io/quote \(imported by use\); to add:\n\tgo get use$'
+go get -d use
+cmp go.sum go.sum.tidy
+go build -n use
+
+-- go.mod --
+module use
+
+go 1.17
+
+require rsc.io/quote v1.5.2
+-- go.sum.tidy --
+golang.org/x/text v0.0.0-20170915032832-14c0d48ead0c h1:pvCbr/wm8HzDD3fVywevekufpn6tCGPY3spdHeZJEsw=
+golang.org/x/text v0.0.0-20170915032832-14c0d48ead0c/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
+rsc.io/quote v1.5.2 h1:3fEykkD9k7lYzXqCYrwGAf7iNhbk4yCjHmKBN9td4L0=
+rsc.io/quote v1.5.2/go.mod h1:LzX7hefJvL54yjefDEDHNONDjII0t9xZLPXsUe+TKr0=
+rsc.io/sampler v1.3.0 h1:HLGR/BgEtI3r0uymSP/nl2uPLsUnNJX8toRyhfpBTII=
+rsc.io/sampler v1.3.0/go.mod h1:T1hPZKmBbMNahiBKFy5HrXp6adAjACjK9JXDnKaTXpA=
+rsc.io/testonly v1.0.0 h1:K/VWHdO+Jv7woUXG0GzVNx1czBXUt3Ib1deaMn+xk64=
+rsc.io/testonly v1.0.0/go.mod h1:OqmGbIFOcF+XrFReLOGZ6BhMM7uMBiQwZsyNmh74SzY=
+-- go.sum.bug --
+golang.org/x/text v0.0.0-20170915032832-14c0d48ead0c h1:pvCbr/wm8HzDD3fVywevekufpn6tCGPY3spdHeZJEsw=
+golang.org/x/text v0.0.0-20170915032832-14c0d48ead0c/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
+rsc.io/quote v1.5.2/go.mod h1:LzX7hefJvL54yjefDEDHNONDjII0t9xZLPXsUe+TKr0=
+rsc.io/sampler v1.3.0 h1:HLGR/BgEtI3r0uymSP/nl2uPLsUnNJX8toRyhfpBTII=
+rsc.io/sampler v1.3.0/go.mod h1:T1hPZKmBbMNahiBKFy5HrXp6adAjACjK9JXDnKaTXpA=
+rsc.io/testonly v1.0.0 h1:K/VWHdO+Jv7woUXG0GzVNx1czBXUt3Ib1deaMn+xk64=
+rsc.io/testonly v1.0.0/go.mod h1:OqmGbIFOcF+XrFReLOGZ6BhMM7uMBiQwZsyNmh74SzY=
+-- use.go --
+package use
+
+import _ "rsc.io/quote"
diff --git a/src/cmd/go/testdata/script/mod_invalid_path_plus.txt b/src/cmd/go/testdata/script/mod_invalid_path_plus.txt
new file mode 100644
index 0000000000..2f2488f01b
--- /dev/null
+++ b/src/cmd/go/testdata/script/mod_invalid_path_plus.txt
@@ -0,0 +1,32 @@
+# https://golang.org/issue/44776
+# The '+' character should be disallowed in module paths, but allowed in package
+# paths within valid modules.
+
+go get -d example.net/cmd
+go list example.net/cmd/x++
+
+! go list -versions -m 'example.net/bad++'
+stderr '^go list -m: module example.net/bad\+\+: malformed module path "example.net/bad\+\+": invalid char ''\+''$'
+
+# TODO(bcmills): 'go get -d example.net/cmd/x++' should also work, but currently
+# it does not. This might be fixed by https://golang.org/cl/297891.
+! go get -d example.net/cmd/x++
+stderr '^go get: malformed module path "example.net/cmd/x\+\+": invalid char ''\+''$'
+
+-- go.mod --
+module example.com/m
+
+go 1.16
+
+replace (
+	example.net/cmd => ./cmd
+)
+
+-- cmd/go.mod --
+module example.net/cmd
+
+go 1.16
+-- cmd/x++/main.go --
+package main
+
+func main() {}
diff --git a/src/cmd/go/testdata/script/mod_verify.txt b/src/cmd/go/testdata/script/mod_verify.txt
index 43812d069f..b5106659a9 100644
--- a/src/cmd/go/testdata/script/mod_verify.txt
+++ b/src/cmd/go/testdata/script/mod_verify.txt
@@ -48,10 +48,13 @@ go mod tidy
 grep '^rsc.io/quote v1.1.0/go.mod ' go.sum
 grep '^rsc.io/quote v1.1.0 ' go.sum
 
-# sync should ignore missing ziphash; verify should not
+# verify should fail on a missing ziphash. tidy should restore it.
 rm $GOPATH/pkg/mod/cache/download/rsc.io/quote/@v/v1.1.0.ziphash
-go mod tidy
 ! go mod verify
+stderr '^rsc.io/quote v1.1.0: missing ziphash: open '$GOPATH'[/\\]pkg[/\\]mod[/\\]cache[/\\]download[/\\]rsc.io[/\\]quote[/\\]@v[/\\]v1.1.0.ziphash'
+go mod tidy
+exists $GOPATH/pkg/mod/cache/download/rsc.io/quote/@v/v1.1.0.ziphash
+go mod verify
 
 # Packages below module root should not be mentioned in go.sum.
 rm go.sum
diff --git a/src/cmd/link/internal/arm/asm.go b/src/cmd/link/internal/arm/asm.go
index 755b472694..03caeae7be 100644
--- a/src/cmd/link/internal/arm/asm.go
+++ b/src/cmd/link/internal/arm/asm.go
@@ -370,10 +370,16 @@ func trampoline(ctxt *ld.Link, ldr *loader.Loader, ri int, rs, s loader.Sym) {
 	r := relocs.At(ri)
 	switch r.Type() {
 	case objabi.R_CALLARM:
-		// r.Add is the instruction
-		// low 24-bit encodes the target address
-		t := (ldr.SymValue(rs) + int64(signext24(r.Add()&0xffffff)*4) - (ldr.SymValue(s) + int64(r.Off()))) / 4
-		if t > 0x7fffff || t < -0x800000 || (*ld.FlagDebugTramp > 1 && ldr.SymPkg(s) != ldr.SymPkg(rs)) {
+		var t int64
+		// ldr.SymValue(rs) == 0 indicates a cross-package jump to a function that is not yet
+		// laid out. Conservatively use a trampoline. This should be rare, as we lay out packages
+		// in dependency order.
+		if ldr.SymValue(rs) != 0 {
+			// r.Add is the instruction
+			// low 24-bit encodes the target address
+			t = (ldr.SymValue(rs) + int64(signext24(r.Add()&0xffffff)*4) - (ldr.SymValue(s) + int64(r.Off()))) / 4
+		}
+		if t > 0x7fffff || t < -0x800000 || ldr.SymValue(rs) == 0 || (*ld.FlagDebugTramp > 1 && ldr.SymPkg(s) != ldr.SymPkg(rs)) {
 			// direct call too far, need to insert trampoline.
 			// look up existing trampolines first. if we found one within the range
 			// of direct call, we can reuse it. otherwise create a new one.
@@ -445,7 +451,7 @@ func gentramp(arch *sys.Arch, linkmode ld.LinkMode, ldr *loader.Loader, tramp *l
 	arch.ByteOrder.PutUint32(P[8:], o3)
 	tramp.SetData(P)
 
-	if linkmode == ld.LinkExternal {
+	if linkmode == ld.LinkExternal || ldr.SymValue(target) == 0 {
 		r, _ := tramp.AddRel(objabi.R_ADDR)
 		r.SetOff(8)
 		r.SetSiz(4)
diff --git a/src/cmd/link/internal/ld/data.go b/src/cmd/link/internal/ld/data.go
index 6013e0ab0a..52035e9630 100644
--- a/src/cmd/link/internal/ld/data.go
+++ b/src/cmd/link/internal/ld/data.go
@@ -106,14 +106,12 @@ func trampoline(ctxt *Link, s loader.Sym) {
 		}
 		rs = ldr.ResolveABIAlias(rs)
 		if ldr.SymValue(rs) == 0 && (ldr.SymType(rs) != sym.SDYNIMPORT && ldr.SymType(rs) != sym.SUNDEFEXT) {
-			if ldr.SymPkg(rs) != ldr.SymPkg(s) {
-				if !isRuntimeDepPkg(ldr.SymPkg(s)) || !isRuntimeDepPkg(ldr.SymPkg(rs)) {
-					ctxt.Errorf(s, "unresolved inter-package jump to %s(%s) from %s", ldr.SymName(rs), ldr.SymPkg(rs), ldr.SymPkg(s))
-				}
-				// runtime and its dependent packages may call to each other.
-				// they are fine, as they will be laid down together.
+			if ldr.SymPkg(rs) == ldr.SymPkg(s) {
+				continue // symbols in the same package are laid out together
+			}
+			if isRuntimeDepPkg(ldr.SymPkg(s)) && isRuntimeDepPkg(ldr.SymPkg(rs)) {
+				continue // runtime packages are laid out together
 			}
-			continue
 		}
 
 		thearch.Trampoline(ctxt, ldr, ri, rs, s)
diff --git a/src/cmd/link/internal/ld/symtab.go b/src/cmd/link/internal/ld/symtab.go
index c98e4de03f..f54cf9ea2f 100644
--- a/src/cmd/link/internal/ld/symtab.go
+++ b/src/cmd/link/internal/ld/symtab.go
@@ -31,6 +31,7 @@
 package ld
 
 import (
+	"cmd/internal/obj"
 	"cmd/internal/objabi"
 	"cmd/link/internal/loader"
 	"cmd/link/internal/sym"
@@ -102,10 +103,14 @@ func putelfsym(ctxt *Link, x loader.Sym, typ elf.SymType, curbind elf.SymBind) {
 		elfshnum = xosect.Elfsect.(*ElfShdr).shnum
 	}
 
+	sname := ldr.SymExtname(x)
+
 	// One pass for each binding: elf.STB_LOCAL, elf.STB_GLOBAL,
 	// maybe one day elf.STB_WEAK.
 	bind := elf.STB_GLOBAL
-	if ldr.IsFileLocal(x) || ldr.AttrVisibilityHidden(x) || ldr.AttrLocal(x) {
+	if ldr.IsFileLocal(x) && !isStaticTmp(sname) || ldr.AttrVisibilityHidden(x) || ldr.AttrLocal(x) {
+		// Static tmp is package local, but a package can be shared among multiple DSOs.
+		// They need to have a single view of the static tmp that are writable.
 		bind = elf.STB_LOCAL
 	}
 
@@ -140,8 +145,6 @@ func putelfsym(ctxt *Link, x loader.Sym, typ elf.SymType, curbind elf.SymBind) {
 		other |= 3 << 5
 	}
 
-	sname := ldr.SymExtname(x)
-
 	// When dynamically linking, we create Symbols by reading the names from
 	// the symbol tables of the shared libraries and so the names need to
 	// match exactly. Tools like DTrace will have to wait for now.
@@ -823,3 +826,7 @@ func setCarrierSize(typ sym.SymKind, sz int64) {
 	}
 	CarrierSymByType[typ].Size = sz
 }
+
+func isStaticTmp(name string) bool {
+	return strings.Contains(name, "."+obj.StaticNamePref)
+}
diff --git a/src/cmd/link/internal/ppc64/asm.go b/src/cmd/link/internal/ppc64/asm.go
index 5bf3898eb9..602f0b5299 100644
--- a/src/cmd/link/internal/ppc64/asm.go
+++ b/src/cmd/link/internal/ppc64/asm.go
@@ -656,13 +656,19 @@ func trampoline(ctxt *ld.Link, ldr *loader.Loader, ri int, rs, s loader.Sym) {
 
 	relocs := ldr.Relocs(s)
 	r := relocs.At(ri)
-	t := ldr.SymValue(rs) + r.Add() - (ldr.SymValue(s) + int64(r.Off()))
+	var t int64
+	// ldr.SymValue(rs) == 0 indicates a cross-package jump to a function that is not yet
+	// laid out. Conservatively use a trampoline. This should be rare, as we lay out packages
+	// in dependency order.
+	if ldr.SymValue(rs) != 0 {
+		t = ldr.SymValue(rs) + r.Add() - (ldr.SymValue(s) + int64(r.Off()))
+	}
 	switch r.Type() {
 	case objabi.R_CALLPOWER:
 
 		// If branch offset is too far then create a trampoline.
 
-		if (ctxt.IsExternal() && ldr.SymSect(s) != ldr.SymSect(rs)) || (ctxt.IsInternal() && int64(int32(t<<6)>>6) != t) || (*ld.FlagDebugTramp > 1 && ldr.SymPkg(s) != ldr.SymPkg(rs)) {
+		if (ctxt.IsExternal() && ldr.SymSect(s) != ldr.SymSect(rs)) || (ctxt.IsInternal() && int64(int32(t<<6)>>6) != t) || ldr.SymValue(rs) == 0 || (*ld.FlagDebugTramp > 1 && ldr.SymPkg(s) != ldr.SymPkg(rs)) {
 			var tramp loader.Sym
 			for i := 0; ; i++ {
 
@@ -749,7 +755,7 @@ func gentramp(ctxt *ld.Link, ldr *loader.Loader, tramp *loader.SymbolBuilder, ta
 
 		// With external linking, the target address must be
 		// relocated using LO and HA
-		if ctxt.IsExternal() {
+		if ctxt.IsExternal() || ldr.SymValue(target) == 0 {
 			r, _ := tramp.AddRel(objabi.R_ADDRPOWER)
 			r.SetOff(0)
 			r.SetSiz(8) // generates 2 relocations: HA + LO
diff --git a/src/cmd/vendor/golang.org/x/mod/module/module.go b/src/cmd/vendor/golang.org/x/mod/module/module.go
index 272baeef17..0e03014837 100644
--- a/src/cmd/vendor/golang.org/x/mod/module/module.go
+++ b/src/cmd/vendor/golang.org/x/mod/module/module.go
@@ -224,12 +224,16 @@ func firstPathOK(r rune) bool {
 		'a' <= r && r <= 'z'
 }
 
-// pathOK reports whether r can appear in an import path element.
+// modPathOK reports whether r can appear in a module path element.
 // Paths can be ASCII letters, ASCII digits, and limited ASCII punctuation: - . _ and ~.
-// This matches what "go get" has historically recognized in import paths.
+//
+// This matches what "go get" has historically recognized in import paths,
+// and avoids confusing sequences like '%20' or '+' that would change meaning
+// if used in a URL.
+//
 // TODO(rsc): We would like to allow Unicode letters, but that requires additional
 // care in the safe encoding (see "escaped paths" above).
-func pathOK(r rune) bool {
+func modPathOK(r rune) bool {
 	if r < utf8.RuneSelf {
 		return r == '-' || r == '.' || r == '_' || r == '~' ||
 			'0' <= r && r <= '9' ||
@@ -239,6 +243,17 @@ func pathOK(r rune) bool {
 	return false
 }
 
+// modPathOK reports whether r can appear in a package import path element.
+//
+// Import paths are intermediate between module paths and file paths: we allow
+// disallow characters that would be confusing or ambiguous as arguments to
+// 'go get' (such as '@' and ' ' ), but allow certain characters that are
+// otherwise-unambiguous on the command line and historically used for some
+// binary names (such as '++' as a suffix for compiler binaries and wrappers).
+func importPathOK(r rune) bool {
+	return modPathOK(r) || r == '+'
+}
+
 // fileNameOK reports whether r can appear in a file name.
 // For now we allow all Unicode letters but otherwise limit to pathOK plus a few more punctuation characters.
 // If we expand the set of allowed characters here, we have to
@@ -394,12 +409,19 @@ func checkElem(elem string, kind pathKind) error {
 	if elem[len(elem)-1] == '.' {
 		return fmt.Errorf("trailing dot in path element")
 	}
-	charOK := pathOK
-	if kind == filePath {
-		charOK = fileNameOK
-	}
 	for _, r := range elem {
-		if !charOK(r) {
+		ok := false
+		switch kind {
+		case modulePath:
+			ok = modPathOK(r)
+		case importPath:
+			ok = importPathOK(r)
+		case filePath:
+			ok = fileNameOK(r)
+		default:
+			panic(fmt.Sprintf("internal error: invalid kind %v", kind))
+		}
+		if !ok {
 			return fmt.Errorf("invalid char %q", r)
 		}
 	}
diff --git a/src/cmd/vendor/modules.txt b/src/cmd/vendor/modules.txt
index 10842768a8..ae2c0a00cc 100644
--- a/src/cmd/vendor/modules.txt
+++ b/src/cmd/vendor/modules.txt
@@ -28,7 +28,7 @@ golang.org/x/arch/x86/x86asm
 golang.org/x/crypto/ed25519
 golang.org/x/crypto/ed25519/internal/edwards25519
 golang.org/x/crypto/ssh/terminal
-# golang.org/x/mod v0.4.2-0.20210302225053-d515b24adc21
+# golang.org/x/mod v0.4.2-0.20210325185522-dbbbf8a3c6ea
 ## explicit
 golang.org/x/mod/internal/lazyregexp
 golang.org/x/mod/modfile
diff --git a/src/run.bash b/src/run.bash
index 706b4b60ee..2123c509f8 100755
--- a/src/run.bash
+++ b/src/run.bash
@@ -23,15 +23,7 @@ fi
 
 eval $(../bin/go env)
 export GOROOT   # The api test requires GOROOT to be set, so set it to match ../bin/go.
-
-# We disallow local import for non-local packages, if $GOROOT happens
-# to be under $GOPATH, then some tests below will fail.  $GOPATH needs
-# to be set to a non-empty string, else Go will set a default value
-# that may also conflict with $GOROOT.  The $GOPATH value doesn't need
-# to point to an actual directory, it just needs to pass the semantic
-# checks performed by Go.  Use $GOROOT to define $GOPATH so that we
-# don't blunder into a user-defined symbolic link.
-export GOPATH=/dev/null
+export GOPATH=/nonexist-gopath
 
 unset CDPATH	# in case user has it set
 export GOBIN=$GOROOT/bin  # Issue 14340
diff --git a/src/run.bat b/src/run.bat
index c299671c13..edcaf52659 100644
--- a/src/run.bat
+++ b/src/run.bat
@@ -18,9 +18,7 @@ setlocal
 

 set GOBUILDFAIL=0

 

-:: we disallow local import for non-local packages, if %GOROOT% happens

-:: to be under %GOPATH%, then some tests below will fail

-set GOPATH=

+set GOPATH=c:\nonexist-gopath

 :: Issue 14340: ignore GOBIN during all.bat.

 set GOBIN=

 set GOFLAGS=

diff --git a/src/run.rc b/src/run.rc
index ab7abfa991..a7b4801207 100755
--- a/src/run.rc
+++ b/src/run.rc
@@ -12,10 +12,9 @@ if(! test -f ../bin/go){
 
 eval `{../bin/go env}
 
-GOPATH = () # we disallow local import for non-local packages, if $GOROOT happens
-            # to be under $GOPATH, then some tests below will fail
-GOBIN = () # Issue 14340
-GOFLAGS = ()
-GO111MODULE = ()
+GOPATH=/nonexist-gopath
+GOBIN=() # Issue 14340
+GOFLAGS=()
+GO111MODULE=()
 
 exec ../bin/go tool dist test -rebuild $*
diff --git a/src/runtime/symtab.go b/src/runtime/symtab.go
index 7667f23f1d..09225fb03a 100644
--- a/src/runtime/symtab.go
+++ b/src/runtime/symtab.go
@@ -102,7 +102,9 @@ func (ci *Frames) Next() (frame Frame, more bool) {
 		name := funcname(funcInfo)
 		if inldata := funcdata(funcInfo, _FUNCDATA_InlTree); inldata != nil {
 			inltree := (*[1 << 20]inlinedCall)(inldata)
-			ix := pcdatavalue(funcInfo, _PCDATA_InlTreeIndex, pc, nil)
+			// Non-strict as cgoTraceback may have added bogus PCs
+			// with a valid funcInfo but invalid PCDATA.
+			ix := pcdatavalue1(funcInfo, _PCDATA_InlTreeIndex, pc, nil, false)
 			if ix >= 0 {
 				// Note: entry is not modified. It always refers to a real frame, not an inlined one.
 				f = nil
diff --git a/src/runtime/symtab_test.go b/src/runtime/symtab_test.go
index 01e5002659..ffa07c7f3a 100644
--- a/src/runtime/symtab_test.go
+++ b/src/runtime/symtab_test.go
@@ -8,6 +8,7 @@ import (
 	"runtime"
 	"strings"
 	"testing"
+	"unsafe"
 )
 
 func TestCaller(t *testing.T) {
@@ -165,3 +166,87 @@ func TestNilName(t *testing.T) {
 		t.Errorf("Name() = %q, want %q", got, "")
 	}
 }
+
+var dummy int
+
+func inlined() {
+	// Side effect to prevent elimination of this entire function.
+	dummy = 42
+}
+
+// A function with an InlTree. Returns a PC within the function body.
+//
+// No inline to ensure this complete function appears in output.
+//
+//go:noinline
+func tracebackFunc(t *testing.T) uintptr {
+	// This body must be more complex than a single call to inlined to get
+	// an inline tree.
+	inlined()
+	inlined()
+
+	// Acquire a PC in this function.
+	pc, _, _, ok := runtime.Caller(0)
+	if !ok {
+		t.Fatalf("Caller(0) got ok false, want true")
+	}
+
+	return pc
+}
+
+// Test that CallersFrames handles PCs in the alignment region between
+// functions (int 3 on amd64) without crashing.
+//
+// Go will never generate a stack trace containing such an address, as it is
+// not a valid call site. However, the cgo traceback function passed to
+// runtime.SetCgoTraceback may not be completely accurate and may incorrect
+// provide PCs in Go code or the alignement region between functions.
+//
+// Go obviously doesn't easily expose the problematic PCs to running programs,
+// so this test is a bit fragile. Some details:
+//
+// * tracebackFunc is our target function. We want to get a PC in the
+//   alignment region following this function. This function also has other
+//   functions inlined into it to ensure it has an InlTree (this was the source
+//   of the bug in issue 44971).
+//
+// * We acquire a PC in tracebackFunc, walking forwards until FuncForPC says
+//   we're in a new function. The last PC of the function according to FuncForPC
+//   should be in the alignment region (assuming the function isn't already
+//   perfectly aligned).
+//
+// This is a regression test for issue 44971.
+func TestFunctionAlignmentTraceback(t *testing.T) {
+	pc := tracebackFunc(t)
+
+	// Double-check we got the right PC.
+	f := runtime.FuncForPC(pc)
+	if !strings.HasSuffix(f.Name(), "tracebackFunc") {
+		t.Fatalf("Caller(0) = %+v, want tracebackFunc", f)
+	}
+
+	// Iterate forward until we find a different function. Back up one
+	// instruction is (hopefully) an alignment instruction.
+	for runtime.FuncForPC(pc) == f {
+		pc++
+	}
+	pc--
+
+	// Is this an alignment region filler instruction? We only check this
+	// on amd64 for simplicity. If this function has no filler, then we may
+	// get a false negative, but will never get a false positive.
+	if runtime.GOARCH == "amd64" {
+		code := *(*uint8)(unsafe.Pointer(pc))
+		if code != 0xcc { // INT $3
+			t.Errorf("PC %v code got %#x want 0xcc", pc, code)
+		}
+	}
+
+	// Finally ensure that Frames.Next doesn't crash when processing this
+	// PC.
+	frames := runtime.CallersFrames([]uintptr{pc})
+	frame, _ := frames.Next()
+	if frame.Func != f {
+		t.Errorf("frames.Next() got %+v want %+v", frame.Func, f)
+	}
+}
diff --git a/src/runtime/time.go b/src/runtime/time.go
index 8ab2a03430..dee6a674e4 100644
--- a/src/runtime/time.go
+++ b/src/runtime/time.go
@@ -263,6 +263,9 @@ func addtimer(t *timer) {
 
 	when := t.when
 
+	// Disable preemption while using pp to avoid changing another P's heap.
+	mp := acquirem()
+
 	pp := getg().m.p.ptr()
 	lock(&pp.timersLock)
 	cleantimers(pp)
@@ -270,6 +273,8 @@ func addtimer(t *timer) {
 	unlock(&pp.timersLock)
 
 	wakeNetPoller(when)
+
+	releasem(mp)
 }
 
 // doaddtimer adds t to the current P's heap.
diff --git a/src/testing/helper_test.go b/src/testing/helper_test.go
index 8858196cf0..b27fd62ee8 100644
--- a/src/testing/helper_test.go
+++ b/src/testing/helper_test.go
@@ -71,6 +71,38 @@ func TestTBHelperParallel(t *T) {
 	}
 }
 
+func TestTBHelperLineNumer(t *T) {
+	var buf bytes.Buffer
+	ctx := newTestContext(1, newMatcher(regexp.MatchString, "", ""))
+	t1 := &T{
+		common: common{
+			signal: make(chan bool),
+			w:      &buf,
+		},
+		context: ctx,
+	}
+	t1.Run("Test", func(t *T) {
+		helperA := func(t *T) {
+			t.Helper()
+			t.Run("subtest", func(t *T) {
+				t.Helper()
+				t.Fatal("fatal error message")
+			})
+		}
+		helperA(t)
+	})
+
+	want := "helper_test.go:92: fatal error message"
+	got := ""
+	lines := strings.Split(strings.TrimSpace(buf.String()), "\n")
+	if len(lines) > 0 {
+		got = strings.TrimSpace(lines[len(lines)-1])
+	}
+	if got != want {
+		t.Errorf("got output:\n\n%v\nwant:\n\n%v", got, want)
+	}
+}
+
 type noopWriter int
 
 func (nw *noopWriter) Write(b []byte) (int, error) { return len(b), nil }
diff --git a/src/testing/testing.go b/src/testing/testing.go
index 80354d5ce8..dec39d24da 100644
--- a/src/testing/testing.go
+++ b/src/testing/testing.go
@@ -509,6 +509,13 @@ func (c *common) frameSkip(skip int) runtime.Frame {
 			}
 			return prevFrame
 		}
+		// If more helper PCs have been added since we last did the conversion
+		if c.helperNames == nil {
+			c.helperNames = make(map[string]struct{})
+			for pc := range c.helperPCs {
+				c.helperNames[pcToName(pc)] = struct{}{}
+			}
+		}
 		if _, ok := c.helperNames[frame.Function]; !ok {
 			// Found a frame that wasn't inside a helper function.
 			return frame
@@ -521,14 +528,6 @@ func (c *common) frameSkip(skip int) runtime.Frame {
 // and inserts the final newline if needed and indentation spaces for formatting.
 // This function must be called with c.mu held.
 func (c *common) decorate(s string, skip int) string {
-	// If more helper PCs have been added since we last did the conversion
-	if c.helperNames == nil {
-		c.helperNames = make(map[string]struct{})
-		for pc := range c.helperPCs {
-			c.helperNames[pcToName(pc)] = struct{}{}
-		}
-	}
-
 	frame := c.frameSkip(skip)
 	file := frame.File
 	line := frame.Line
diff --git a/src/time/sleep_test.go b/src/time/sleep_test.go
index 084ac33f51..6ee0631a85 100644
--- a/src/time/sleep_test.go
+++ b/src/time/sleep_test.go
@@ -511,6 +511,22 @@ func TestZeroTimerStopPanics(t *testing.T) {
 	tr.Stop()
 }
 
+// Test that zero duration timers aren't missed by the scheduler. Regression test for issue 44868.
+func TestZeroTimer(t *testing.T) {
+	if testing.Short() {
+		t.Skip("-short")
+	}
+
+	for i := 0; i < 1000000; i++ {
+		s := Now()
+		ti := NewTimer(0)
+		<-ti.C
+		if diff := Since(s); diff > 2*Second {
+			t.Errorf("Expected time to get value from Timer channel in less than 2 sec, took %v", diff)
+		}
+	}
+}
+
 // Benchmark timer latency when the thread that creates the timer is busy with
 // other work and the timers must be serviced by other threads.
 // https://golang.org/issue/38860
diff --git a/test/codegen/bits.go b/test/codegen/bits.go
index 4508eba487..6f7502292a 100644
--- a/test/codegen/bits.go
+++ b/test/codegen/bits.go
@@ -262,8 +262,8 @@ func bitcompl32(a, b uint32) (n uint32) {
 	return n
 }
 
-// check direct operation on memory with constant source
-func bitOpOnMem(a []uint32) {
+// check direct operation on memory with constant and shifted constant sources
+func bitOpOnMem(a []uint32, b, c, d uint32) {
 	// amd64:`ANDL\s[$]200,\s\([A-Z]+\)`
 	a[0] &= 200
 	// amd64:`ORL\s[$]220,\s4\([A-Z]+\)`
@@ -276,6 +276,12 @@ func bitOpOnMem(a []uint32) {
 	a[4] |= 0x4000
 	// amd64:`BTCL\s[$]13,\s20\([A-Z]+\)`,-`XORL`
 	a[5] ^= 0x2000
+	// amd64:`BTRL\s[A-Z]+,\s24\([A-Z]+\)`
+	a[6] &^= 1 << (b & 31)
+	// amd64:`BTSL\s[A-Z]+,\s28\([A-Z]+\)`
+	a[7] |= 1 << (c & 31)
+	// amd64:`BTCL\s[A-Z]+,\s32\([A-Z]+\)`
+	a[8] ^= 1 << (d & 31)
 }
 
 func bitcheckMostNegative(b uint8) bool {
diff --git a/test/fixedbugs/issue45175.go b/test/fixedbugs/issue45175.go
new file mode 100644
index 0000000000..02dfe8a0a9
--- /dev/null
+++ b/test/fixedbugs/issue45175.go
@@ -0,0 +1,29 @@
+// run
+
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+//go:noinline
+func f(c bool) int {
+	b := true
+	x := 0
+	y := 1
+	for b {
+		b = false
+		y = x
+		x = 2
+		if c {
+			return 3
+		}
+	}
+	return y
+}
+
+func main() {
+	if got := f(false); got != 0 {
+		panic(got)
+	}
+}