[dev.boringcrypto.go1.13] all: merge go1.13.12 into dev.boringcrypto.go1.13

Change-Id: I34cc756b36cad8c9583d64db2d23c74c14b894c3

7 files changed, 197 insertions, 50 deletions

diff --git a/src/cmd/compile/internal/ssa/regalloc.go b/src/cmd/compile/internal/ssa/regalloc.go
index 8abbf61507..e92ab00e95 100644
--- a/src/cmd/compile/internal/ssa/regalloc.go
+++ b/src/cmd/compile/internal/ssa/regalloc.go
@@ -976,25 +976,22 @@ func (s *regAllocState) regalloc(f *Func) {
 				}
 			}
 
-			// Second pass - deallocate any phi inputs which are now dead.
+			// Second pass - deallocate all in-register phi inputs.
 			for i, v := range phis {
 				if !s.values[v.ID].needReg {
 					continue
 				}
 				a := v.Args[idx]
-				if !regValLiveSet.contains(a.ID) {
-					// Input is dead beyond the phi, deallocate
-					// anywhere else it might live.
-					s.freeRegs(s.values[a.ID].regs)
-				} else {
-					// Input is still live.
+				r := phiRegs[i]
+				if r == noRegister {
+					continue
+				}
+				if regValLiveSet.contains(a.ID) {
+					// Input value is still live (it is used by something other than Phi).
 					// Try to move it around before kicking out, if there is a free register.
 					// We generate a Copy in the predecessor block and record it. It will be
-					// deleted if never used.
-					r := phiRegs[i]
-					if r == noRegister {
-						continue
-					}
+					// deleted later if never used.
+					//
 					// Pick a free register. At this point some registers used in the predecessor
 					// block may have been deallocated. Those are the ones used for Phis. Exclude
 					// them (and they are not going to be helpful anyway).
@@ -1010,8 +1007,8 @@ func (s *regAllocState) regalloc(f *Func) {
 						s.assignReg(r2, a, c)
 						s.endRegs[p.ID] = append(s.endRegs[p.ID], endReg{r2, a, c})
 					}
-					s.freeReg(r)
 				}
+				s.freeReg(r)
 			}
 
 			// Copy phi ops into new schedule.
@@ -1842,6 +1839,11 @@ func (s *regAllocState) shuffle(stacklive [][]ID) {
 			e.process()
 		}
 	}
+
+	if s.f.pass.debug > regDebug {
+		fmt.Printf("post shuffle %s\n", s.f.Name)
+		fmt.Println(s.f.String())
+	}
 }
 
 type edgeState struct {
diff --git a/src/math/big/rat.go b/src/math/big/rat.go
index c8bf698b18..d35cd4cbd1 100644
--- a/src/math/big/rat.go
+++ b/src/math/big/rat.go
@@ -22,7 +22,9 @@ import (
 // of Rats are not supported and may lead to errors.
 type Rat struct {
 	// To make zero values for Rat work w/o initialization,
-	// a zero value of b (len(b) == 0) acts like b == 1.
+	// a zero value of b (len(b) == 0) acts like b == 1. At
+	// the earliest opportunity (when an assignment to the Rat
+	// is made), such uninitialized denominators are set to 1.
 	// a.neg determines the sign of the Rat, b.neg is ignored.
 	a, b Int
 }
@@ -271,7 +273,7 @@ func quotToFloat64(a, b nat) (f float64, exact bool) {
 func (x *Rat) Float32() (f float32, exact bool) {
 	b := x.b.abs
 	if len(b) == 0 {
-		b = b.set(natOne) // materialize denominator
+		b = natOne
 	}
 	f, exact = quotToFloat32(x.a.abs, b)
 	if x.a.neg {
@@ -287,7 +289,7 @@ func (x *Rat) Float32() (f float32, exact bool) {
 func (x *Rat) Float64() (f float64, exact bool) {
 	b := x.b.abs
 	if len(b) == 0 {
-		b = b.set(natOne) // materialize denominator
+		b = natOne
 	}
 	f, exact = quotToFloat64(x.a.abs, b)
 	if x.a.neg {
@@ -297,6 +299,7 @@ func (x *Rat) Float64() (f float64, exact bool) {
 }
 
 // SetFrac sets z to a/b and returns z.
+// If b == 0, SetFrac panics.
 func (z *Rat) SetFrac(a, b *Int) *Rat {
 	z.a.neg = a.neg != b.neg
 	babs := b.abs
@@ -312,11 +315,12 @@ func (z *Rat) SetFrac(a, b *Int) *Rat {
 }
 
 // SetFrac64 sets z to a/b and returns z.
+// If b == 0, SetFrac64 panics.
 func (z *Rat) SetFrac64(a, b int64) *Rat {
-	z.a.SetInt64(a)
 	if b == 0 {
 		panic("division by zero")
 	}
+	z.a.SetInt64(a)
 	if b < 0 {
 		b = -b
 		z.a.neg = !z.a.neg
@@ -328,21 +332,21 @@ func (z *Rat) SetFrac64(a, b int64) *Rat {
 // SetInt sets z to x (by making a copy of x) and returns z.
 func (z *Rat) SetInt(x *Int) *Rat {
 	z.a.Set(x)
-	z.b.abs = z.b.abs[:0]
+	z.b.abs = z.b.abs.setWord(1)
 	return z
 }
 
 // SetInt64 sets z to x and returns z.
 func (z *Rat) SetInt64(x int64) *Rat {
 	z.a.SetInt64(x)
-	z.b.abs = z.b.abs[:0]
+	z.b.abs = z.b.abs.setWord(1)
 	return z
 }
 
 // SetUint64 sets z to x and returns z.
 func (z *Rat) SetUint64(x uint64) *Rat {
 	z.a.SetUint64(x)
-	z.b.abs = z.b.abs[:0]
+	z.b.abs = z.b.abs.setWord(1)
 	return z
 }
 
@@ -352,6 +356,9 @@ func (z *Rat) Set(x *Rat) *Rat {
 		z.a.Set(&x.a)
 		z.b.Set(&x.b)
 	}
+	if len(z.b.abs) == 0 {
+		z.b.abs = z.b.abs.setWord(1)
+	}
 	return z
 }
 
@@ -370,20 +377,13 @@ func (z *Rat) Neg(x *Rat) *Rat {
 }
 
 // Inv sets z to 1/x and returns z.
+// If x == 0, Inv panics.
 func (z *Rat) Inv(x *Rat) *Rat {
 	if len(x.a.abs) == 0 {
 		panic("division by zero")
 	}
 	z.Set(x)
-	a := z.b.abs
-	if len(a) == 0 {
-		a = a.set(natOne) // materialize numerator
-	}
-	b := z.a.abs
-	if b.cmp(natOne) == 0 {
-		b = b[:0] // normalize denominator
-	}
-	z.a.abs, z.b.abs = a, b // sign doesn't change
+	z.a.abs, z.b.abs = z.b.abs, z.a.abs
 	return z
 }
 
@@ -411,12 +411,19 @@ func (x *Rat) Num() *Int {
 }
 
 // Denom returns the denominator of x; it is always > 0.
-// The result is a reference to x's denominator; it
+// The result is a reference to x's denominator, unless
+// x is an uninitialized (zero value) Rat, in which case
+// the result is a new Int of value 1. (To initialize x,
+// any operation that sets x will do, including x.Set(x).)
+// If the result is a reference to x's denominator it
 // may change if a new value is assigned to x, and vice versa.
 func (x *Rat) Denom() *Int {
 	x.b.neg = false // the result is always >= 0
 	if len(x.b.abs) == 0 {
-		x.b.abs = x.b.abs.set(natOne) // materialize denominator
+		// Note: If this proves problematic, we could
+		//       panic instead and require the Rat to
+		//       be explicitly initialized.
+		return &Int{abs: nat{1}}
 	}
 	return &x.b
 }
@@ -424,25 +431,20 @@ func (x *Rat) Denom() *Int {
 func (z *Rat) norm() *Rat {
 	switch {
 	case len(z.a.abs) == 0:
-		// z == 0 - normalize sign and denominator
+		// z == 0; normalize sign and denominator
 		z.a.neg = false
-		z.b.abs = z.b.abs[:0]
+		fallthrough
 	case len(z.b.abs) == 0:
-		// z is normalized int - nothing to do
-	case z.b.abs.cmp(natOne) == 0:
-		// z is int - normalize denominator
-		z.b.abs = z.b.abs[:0]
+		// z is integer; normalize denominator
+		z.b.abs = z.b.abs.setWord(1)
 	default:
+		// z is fraction; normalize numerator and denominator
 		neg := z.a.neg
 		z.a.neg = false
 		z.b.neg = false
 		if f := NewInt(0).lehmerGCD(nil, nil, &z.a, &z.b); f.Cmp(intOne) != 0 {
 			z.a.abs, _ = z.a.abs.div(nil, z.a.abs, f.abs)
 			z.b.abs, _ = z.b.abs.div(nil, z.b.abs, f.abs)
-			if z.b.abs.cmp(natOne) == 0 {
-				// z is int - normalize denominator
-				z.b.abs = z.b.abs[:0]
-			}
 		}
 		z.a.neg = neg
 	}
@@ -454,6 +456,8 @@ func (z *Rat) norm() *Rat {
 // returns z.
 func mulDenom(z, x, y nat) nat {
 	switch {
+	case len(x) == 0 && len(y) == 0:
+		return z.setWord(1)
 	case len(x) == 0:
 		return z.set(y)
 	case len(y) == 0:
@@ -509,10 +513,14 @@ func (z *Rat) Sub(x, y *Rat) *Rat {
 // Mul sets z to the product x*y and returns z.
 func (z *Rat) Mul(x, y *Rat) *Rat {
 	if x == y {
-		// a squared Rat is positive and can't be reduced
+		// a squared Rat is positive and can't be reduced (no need to call norm())
 		z.a.neg = false
 		z.a.abs = z.a.abs.sqr(x.a.abs)
-		z.b.abs = z.b.abs.sqr(x.b.abs)
+		if len(x.b.abs) == 0 {
+			z.b.abs = z.b.abs.setWord(1)
+		} else {
+			z.b.abs = z.b.abs.sqr(x.b.abs)
+		}
 		return z
 	}
 	z.a.Mul(&x.a, &y.a)
@@ -521,7 +529,7 @@ func (z *Rat) Mul(x, y *Rat) *Rat {
 }
 
 // Quo sets z to the quotient x/y and returns z.
-// If y == 0, a division-by-zero run-time panic occurs.
+// If y == 0, Quo panics.
 func (z *Rat) Quo(x, y *Rat) *Rat {
 	if len(y.a.abs) == 0 {
 		panic("division by zero")
diff --git a/src/math/big/rat_test.go b/src/math/big/rat_test.go
index 83c5d5cfea..02569c1b16 100644
--- a/src/math/big/rat_test.go
+++ b/src/math/big/rat_test.go
@@ -329,18 +329,40 @@ func TestIssue3521(t *testing.T) {
 		t.Errorf("0) got %s want %s", zero.Denom(), one)
 	}
 
-	// 1a) a zero value remains zero independent of denominator
+	// 1a) the denominator of an (uninitialized) zero value is not shared with the value
+	s := &zero.b
+	d := zero.Denom()
+	if d == s {
+		t.Errorf("1a) got %s (%p) == %s (%p) want different *Int values", d, d, s, s)
+	}
+
+	// 1b) the denominator of an (uninitialized) value is a new 1 each time
+	d1 := zero.Denom()
+	d2 := zero.Denom()
+	if d1 == d2 {
+		t.Errorf("1b) got %s (%p) == %s (%p) want different *Int values", d1, d1, d2, d2)
+	}
+
+	// 1c) the denominator of an initialized zero value is shared with the value
 	x := new(Rat)
+	x.Set(x) // initialize x (any operation that sets x explicitly will do)
+	s = &x.b
+	d = x.Denom()
+	if d != s {
+		t.Errorf("1c) got %s (%p) != %s (%p) want identical *Int values", d, d, s, s)
+	}
+
+	// 1d) a zero value remains zero independent of denominator
 	x.Denom().Set(new(Int).Neg(b))
 	if x.Cmp(zero) != 0 {
-		t.Errorf("1a) got %s want %s", x, zero)
+		t.Errorf("1d) got %s want %s", x, zero)
 	}
 
-	// 1b) a zero value may have a denominator != 0 and != 1
+	// 1e) a zero value may have a denominator != 0 and != 1
 	x.Num().Set(a)
 	qab := new(Rat).SetFrac(a, b)
 	if x.Cmp(qab) != 0 {
-		t.Errorf("1b) got %s want %s", x, qab)
+		t.Errorf("1e) got %s want %s", x, qab)
 	}
 
 	// 2a) an integral value becomes a fraction depending on denominator
@@ -678,3 +700,29 @@ func BenchmarkRatCmp(b *testing.B) {
 		x.Cmp(y)
 	}
 }
+
+// TestIssue34919 verifies that a Rat's denominator is not modified
+// when simply accessing the Rat value.
+func TestIssue34919(t *testing.T) {
+	for _, acc := range []struct {
+		name string
+		f    func(*Rat)
+	}{
+		{"Float32", func(x *Rat) { x.Float32() }},
+		{"Float64", func(x *Rat) { x.Float64() }},
+		{"Inv", func(x *Rat) { new(Rat).Inv(x) }},
+		{"Sign", func(x *Rat) { x.Sign() }},
+		{"IsInt", func(x *Rat) { x.IsInt() }},
+		{"Num", func(x *Rat) { x.Num() }},
+		// {"Denom", func(x *Rat) { x.Denom() }}, TODO(gri) should we change the API? See issue #33792.
+	} {
+		// A denominator of length 0 is interpreted as 1. Make sure that
+		// "materialization" of the denominator doesn't lead to setting
+		// the underlying array element 0 to 1.
+		r := &Rat{Int{abs: nat{991}}, Int{abs: make(nat, 0, 1)}}
+		acc.f(r)
+		if d := r.b.abs[:1][0]; d != 0 {
+			t.Errorf("%s modified denominator: got %d, want 0", acc.name, d)
+		}
+	}
+}
diff --git a/src/runtime/crash_test.go b/src/runtime/crash_test.go
index c54bb57da2..ac0344e9a3 100644
--- a/src/runtime/crash_test.go
+++ b/src/runtime/crash_test.go
@@ -55,6 +55,16 @@ func runTestProg(t *testing.T, binary, name string, env ...string) string {
 		t.Fatal(err)
 	}
 
+	return runBuiltTestProg(t, exe, name, env...)
+}
+
+func runBuiltTestProg(t *testing.T, exe, name string, env ...string) string {
+	if *flagQuick {
+		t.Skip("-quick")
+	}
+
+	testenv.MustHaveGoBuild(t)
+
 	cmd := testenv.CleanCmdEnv(exec.Command(exe, name))
 	cmd.Env = append(cmd.Env, env...)
 	if testing.Short() {
@@ -64,7 +74,7 @@ func runTestProg(t *testing.T, binary, name string, env ...string) string {
 	cmd.Stdout = &b
 	cmd.Stderr = &b
 	if err := cmd.Start(); err != nil {
-		t.Fatalf("starting %s %s: %v", binary, name, err)
+		t.Fatalf("starting %s %s: %v", exe, name, err)
 	}
 
 	// If the process doesn't complete within 1 minute,
@@ -92,7 +102,7 @@ func runTestProg(t *testing.T, binary, name string, env ...string) string {
 	}()
 
 	if err := cmd.Wait(); err != nil {
-		t.Logf("%s %s exit status: %v", binary, name, err)
+		t.Logf("%s %s exit status: %v", exe, name, err)
 	}
 	close(done)
 
diff --git a/src/runtime/proc.go b/src/runtime/proc.go
index 93d329d15e..3723f84a05 100644
--- a/src/runtime/proc.go
+++ b/src/runtime/proc.go
@@ -1862,10 +1862,16 @@ func startTemplateThread() {
 	if GOARCH == "wasm" { // no threads on wasm yet
 		return
 	}
+
+	// Disable preemption to guarantee that the template thread will be
+	// created before a park once haveTemplateThread is set.
+	mp := acquirem()
 	if !atomic.Cas(&newmHandoff.haveTemplateThread, 0, 1) {
+		releasem(mp)
 		return
 	}
 	newm(templateThread, nil)
+	releasem(mp)
 }
 
 // templateThread is a thread in a known-good state that exists solely
diff --git a/src/runtime/proc_test.go b/src/runtime/proc_test.go
index 6e6272e80a..108be6a881 100644
--- a/src/runtime/proc_test.go
+++ b/src/runtime/proc_test.go
@@ -6,6 +6,7 @@ package runtime_test
 
 import (
 	"fmt"
+	"internal/testenv"
 	"math"
 	"net"
 	"runtime"
@@ -912,6 +913,29 @@ func TestLockOSThreadAvoidsStatePropagation(t *testing.T) {
 	}
 }
 
+func TestLockOSThreadTemplateThreadRace(t *testing.T) {
+	testenv.MustHaveGoRun(t)
+
+	exe, err := buildTestProg(t, "testprog")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	iterations := 100
+	if testing.Short() {
+		// Reduce run time to ~100ms, with much lower probability of
+		// catching issues.
+		iterations = 5
+	}
+	for i := 0; i < iterations; i++ {
+		want := "OK\n"
+		output := runBuiltTestProg(t, exe, "LockOSThreadTemplateThreadRace")
+		if output != want {
+			t.Fatalf("run %d: want %q, got %q", i, want, output)
+		}
+	}
+}
+
 // fakeSyscall emulates a system call.
 //go:nosplit
 func fakeSyscall(duration time.Duration) {
diff --git a/src/runtime/testdata/testprog/lockosthread.go b/src/runtime/testdata/testprog/lockosthread.go
index fd3123e647..098cc4dd72 100644
--- a/src/runtime/testdata/testprog/lockosthread.go
+++ b/src/runtime/testdata/testprog/lockosthread.go
@@ -7,6 +7,7 @@ package main
 import (
 	"os"
 	"runtime"
+	"sync"
 	"time"
 )
 
@@ -30,6 +31,7 @@ func init() {
 		runtime.LockOSThread()
 	})
 	register("LockOSThreadAvoidsStatePropagation", LockOSThreadAvoidsStatePropagation)
+	register("LockOSThreadTemplateThreadRace", LockOSThreadTemplateThreadRace)
 }
 
 func LockOSThreadMain() {
@@ -195,3 +197,50 @@ func LockOSThreadAvoidsStatePropagation() {
 	runtime.UnlockOSThread()
 	println("OK")
 }
+
+func LockOSThreadTemplateThreadRace() {
+	// This test attempts to reproduce the race described in
+	// golang.org/issue/38931. To do so, we must have a stop-the-world
+	// (achieved via ReadMemStats) racing with two LockOSThread calls.
+	//
+	// While this test attempts to line up the timing, it is only expected
+	// to fail (and thus hang) around 2% of the time if the race is
+	// present.
+
+	// Ensure enough Ps to actually run everything in parallel. Though on
+	// <4 core machines, we are still at the whim of the kernel scheduler.
+	runtime.GOMAXPROCS(4)
+
+	go func() {
+		// Stop the world; race with LockOSThread below.
+		var m runtime.MemStats
+		for {
+			runtime.ReadMemStats(&m)
+		}
+	}()
+
+	// Try to synchronize both LockOSThreads.
+	start := time.Now().Add(10*time.Millisecond)
+
+	var wg sync.WaitGroup
+	wg.Add(2)
+
+	for i := 0; i < 2; i++ {
+		go func() {
+			for time.Now().Before(start) {
+			}
+
+			// Add work to the local runq to trigger early startm
+			// in handoffp.
+			go func(){}()
+
+			runtime.LockOSThread()
+			runtime.Gosched()  // add a preemption point.
+			wg.Done()
+		}()
+	}
+
+	wg.Wait()
+	// If both LockOSThreads completed then we did not hit the race.
+	println("OK")
+}