[release-branch.go1.21] cmd/compile: ensure pointer arithmetic happens after the nil check

Have nil checks return a pointer that is known non-nil. Users of
that pointer can use the result, ensuring that they are ordered
after the nil check itself.

The order dependence goes away after scheduling, when we've fixed
an order. At that point we move uses back to the original pointer
so it doesn't change regalloc any.

This prevents pointer arithmetic on nil from being spilled to the
stack and then observed by a stack scan.

Fixes #63743

Change-Id: I1a5fa4f2e6d9000d672792b4f90dfc1b7b67f6ea
Reviewed-on: https://go-review.googlesource.com/c/go/+/537775
Reviewed-by: David Chase <drchase@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@google.com>
(cherry picked from commit 962ccbef91057f91518443b648e02fc3afe8c764)
Reviewed-on: https://go-review.googlesource.com/c/go/+/538717
Auto-Submit: Heschi Kreinick <heschi@google.com>
Reviewed-by: Heschi Kreinick <heschi@google.com>

15 files changed, 179 insertions, 81 deletions

diff --git a/src/cmd/compile/internal/ssa/_gen/generic.rules b/src/cmd/compile/internal/ssa/_gen/generic.rules
index cdb346321e5..d3af465d0e0 100644
--- a/src/cmd/compile/internal/ssa/_gen/generic.rules
+++ b/src/cmd/compile/internal/ssa/_gen/generic.rules
@@ -981,7 +981,7 @@
     (ConstNil <typ.Uintptr>)
     (ConstNil <typ.BytePtr>))
 
-(NilCheck (GetG mem) mem) => mem
+(NilCheck ptr:(GetG mem) mem) => ptr
 
 (If (Not cond) yes no) => (If cond no yes)
 (If (ConstBool [c]) yes no) && c => (First yes no)
@@ -2055,19 +2055,19 @@
 	&& isSameCall(call.Aux, "runtime.newobject")
 	=> mem
 
-(NilCheck (SelectN [0] call:(StaticLECall _ _)) _)
+(NilCheck ptr:(SelectN [0] call:(StaticLECall _ _)) _)
 	&& isSameCall(call.Aux, "runtime.newobject")
 	&& warnRule(fe.Debug_checknil(), v, "removed nil check")
-	=> (Invalid)
+	=> ptr
 
-(NilCheck (OffPtr (SelectN [0] call:(StaticLECall _ _))) _)
+(NilCheck ptr:(OffPtr (SelectN [0] call:(StaticLECall _ _))) _)
 	&& isSameCall(call.Aux, "runtime.newobject")
 	&& warnRule(fe.Debug_checknil(), v, "removed nil check")
-	=> (Invalid)
+	=> ptr
 
 // Addresses of globals are always non-nil.
-(NilCheck          (Addr {_} (SB))    _) => (Invalid)
-(NilCheck (Convert (Addr {_} (SB)) _) _) => (Invalid)
+(NilCheck          ptr:(Addr {_} (SB))    _) => ptr
+(NilCheck ptr:(Convert (Addr {_} (SB)) _) _) => ptr
 
 // for late-expanded calls, recognize memequal applied to a single constant byte
 // Support is limited by 1, 2, 4, 8 byte sizes
diff --git a/src/cmd/compile/internal/ssa/_gen/genericOps.go b/src/cmd/compile/internal/ssa/_gen/genericOps.go
index 53ff57f6b12..aa5fb0e03e6 100644
--- a/src/cmd/compile/internal/ssa/_gen/genericOps.go
+++ b/src/cmd/compile/internal/ssa/_gen/genericOps.go
@@ -471,7 +471,7 @@ var genericOps = []opData{
 	{name: "IsNonNil", argLength: 1, typ: "Bool"},        // arg0 != nil
 	{name: "IsInBounds", argLength: 2, typ: "Bool"},      // 0 <= arg0 < arg1. arg1 is guaranteed >= 0.
 	{name: "IsSliceInBounds", argLength: 2, typ: "Bool"}, // 0 <= arg0 <= arg1. arg1 is guaranteed >= 0.
-	{name: "NilCheck", argLength: 2, typ: "Void"},        // arg0=ptr, arg1=mem. Panics if arg0 is nil. Returns void.
+	{name: "NilCheck", argLength: 2, nilCheck: true},     // arg0=ptr, arg1=mem. Panics if arg0 is nil. Returns the ptr unmodified.
 
 	// Pseudo-ops
 	{name: "GetG", argLength: 1, zeroWidth: true}, // runtime.getg() (read g pointer). arg0=mem
diff --git a/src/cmd/compile/internal/ssa/check.go b/src/cmd/compile/internal/ssa/check.go
index f34b9074197..bbfdaceaad9 100644
--- a/src/cmd/compile/internal/ssa/check.go
+++ b/src/cmd/compile/internal/ssa/check.go
@@ -317,7 +317,28 @@ func checkFunc(f *Func) {
 				if !v.Aux.(*ir.Name).Type().HasPointers() {
 					f.Fatalf("vardef must have pointer type %s", v.Aux.(*ir.Name).Type().String())
 				}
-
+			case OpNilCheck:
+				// nil checks have pointer type before scheduling, and
+				// void type after scheduling.
+				if f.scheduled {
+					if v.Uses != 0 {
+						f.Fatalf("nilcheck must have 0 uses %s", v.Uses)
+					}
+					if !v.Type.IsVoid() {
+						f.Fatalf("nilcheck must have void type %s", v.Type.String())
+					}
+				} else {
+					if !v.Type.IsPtrShaped() && !v.Type.IsUintptr() {
+						f.Fatalf("nilcheck must have pointer type %s", v.Type.String())
+					}
+				}
+				if !v.Args[0].Type.IsPtrShaped() && !v.Args[0].Type.IsUintptr() {
+					f.Fatalf("nilcheck must have argument of pointer type %s", v.Args[0].Type.String())
+				}
+				if !v.Args[1].Type.IsMemory() {
+					f.Fatalf("bad arg 1 type to %s: want mem, have %s",
+						v.Op, v.Args[1].Type.String())
+				}
 			}
 
 			// TODO: check for cycles in values
diff --git a/src/cmd/compile/internal/ssa/deadcode.go b/src/cmd/compile/internal/ssa/deadcode.go
index 52cc7f2ca74..ae9fd2ef242 100644
--- a/src/cmd/compile/internal/ssa/deadcode.go
+++ b/src/cmd/compile/internal/ssa/deadcode.go
@@ -110,16 +110,15 @@ func liveValues(f *Func, reachable []bool) (live []bool, liveOrderStmts []*Value
 			}
 		}
 		for _, v := range b.Values {
-			if (opcodeTable[v.Op].call || opcodeTable[v.Op].hasSideEffects) && !live[v.ID] {
+			if (opcodeTable[v.Op].call || opcodeTable[v.Op].hasSideEffects || opcodeTable[v.Op].nilCheck) && !live[v.ID] {
 				live[v.ID] = true
 				q = append(q, v)
 				if v.Pos.IsStmt() != src.PosNotStmt {
 					liveOrderStmts = append(liveOrderStmts, v)
 				}
 			}
-			if v.Type.IsVoid() && !live[v.ID] {
-				// The only Void ops are nil checks and inline marks.  We must keep these.
-				if v.Op == OpInlMark && !liveInlIdx[int(v.AuxInt)] {
+			if v.Op == OpInlMark {
+				if !liveInlIdx[int(v.AuxInt)] {
 					// We don't need marks for bodies that
 					// have been completely optimized away.
 					// TODO: save marks only for bodies which
diff --git a/src/cmd/compile/internal/ssa/deadstore.go b/src/cmd/compile/internal/ssa/deadstore.go
index 7656e45cb9d..cb3427103c5 100644
--- a/src/cmd/compile/internal/ssa/deadstore.go
+++ b/src/cmd/compile/internal/ssa/deadstore.go
@@ -249,7 +249,7 @@ func elimDeadAutosGeneric(f *Func) {
 		}
 
 		if v.Uses == 0 && v.Op != OpNilCheck && !v.Op.IsCall() && !v.Op.HasSideEffects() || len(args) == 0 {
-			// Nil check has no use, but we need to keep it.
+			// We need to keep nil checks even if they have no use.
 			// Also keep calls and values that have side effects.
 			return
 		}
diff --git a/src/cmd/compile/internal/ssa/fuse.go b/src/cmd/compile/internal/ssa/fuse.go
index 6d3fb707805..68defde7b4b 100644
--- a/src/cmd/compile/internal/ssa/fuse.go
+++ b/src/cmd/compile/internal/ssa/fuse.go
@@ -169,7 +169,7 @@ func fuseBlockIf(b *Block) bool {
 // There may be false positives.
 func isEmpty(b *Block) bool {
 	for _, v := range b.Values {
-		if v.Uses > 0 || v.Op.IsCall() || v.Op.HasSideEffects() || v.Type.IsVoid() {
+		if v.Uses > 0 || v.Op.IsCall() || v.Op.HasSideEffects() || v.Type.IsVoid() || opcodeTable[v.Op].nilCheck {
 			return false
 		}
 	}
diff --git a/src/cmd/compile/internal/ssa/fuse_test.go b/src/cmd/compile/internal/ssa/fuse_test.go
index fa7921a18f6..2f89938d1d9 100644
--- a/src/cmd/compile/internal/ssa/fuse_test.go
+++ b/src/cmd/compile/internal/ssa/fuse_test.go
@@ -254,7 +254,7 @@ func TestFuseSideEffects(t *testing.T) {
 			Valu("p", OpArg, c.config.Types.IntPtr, 0, nil),
 			If("c1", "z0", "exit")),
 		Bloc("z0",
-			Valu("nilcheck", OpNilCheck, types.TypeVoid, 0, nil, "p", "mem"),
+			Valu("nilcheck", OpNilCheck, c.config.Types.IntPtr, 0, nil, "p", "mem"),
 			Goto("exit")),
 		Bloc("exit",
 			Exit("mem"),
diff --git a/src/cmd/compile/internal/ssa/nilcheck.go b/src/cmd/compile/internal/ssa/nilcheck.go
index 4f797a473f7..c69cd8c32ed 100644
--- a/src/cmd/compile/internal/ssa/nilcheck.go
+++ b/src/cmd/compile/internal/ssa/nilcheck.go
@@ -38,11 +38,14 @@ func nilcheckelim(f *Func) {
 	work := make([]bp, 0, 256)
 	work = append(work, bp{block: f.Entry})
 
-	// map from value ID to bool indicating if value is known to be non-nil
-	// in the current dominator path being walked. This slice is updated by
+	// map from value ID to known non-nil version of that value ID
+	// (in the current dominator path being walked). This slice is updated by
 	// walkStates to maintain the known non-nil values.
-	nonNilValues := f.Cache.allocBoolSlice(f.NumValues())
-	defer f.Cache.freeBoolSlice(nonNilValues)
+	// If there is extrinsic information about non-nil-ness, this map
+	// points a value to itself. If a value is known non-nil because we
+	// already did a nil check on it, it points to the nil check operation.
+	nonNilValues := f.Cache.allocValueSlice(f.NumValues())
+	defer f.Cache.freeValueSlice(nonNilValues)
 
 	// make an initial pass identifying any non-nil values
 	for _, b := range f.Blocks {
@@ -54,7 +57,7 @@ func nilcheckelim(f *Func) {
 			// We assume that SlicePtr is non-nil because we do a bounds check
 			// before the slice access (and all cap>0 slices have a non-nil ptr). See #30366.
 			if v.Op == OpAddr || v.Op == OpLocalAddr || v.Op == OpAddPtr || v.Op == OpOffPtr || v.Op == OpAdd32 || v.Op == OpAdd64 || v.Op == OpSub32 || v.Op == OpSub64 || v.Op == OpSlicePtr {
-				nonNilValues[v.ID] = true
+				nonNilValues[v.ID] = v
 			}
 		}
 	}
@@ -68,16 +71,16 @@ func nilcheckelim(f *Func) {
 				if v.Op == OpPhi {
 					argsNonNil := true
 					for _, a := range v.Args {
-						if !nonNilValues[a.ID] {
+						if nonNilValues[a.ID] == nil {
 							argsNonNil = false
 							break
 						}
 					}
 					if argsNonNil {
-						if !nonNilValues[v.ID] {
+						if nonNilValues[v.ID] == nil {
 							changed = true
 						}
-						nonNilValues[v.ID] = true
+						nonNilValues[v.ID] = v
 					}
 				}
 			}
@@ -103,8 +106,8 @@ func nilcheckelim(f *Func) {
 			if len(b.Preds) == 1 {
 				p := b.Preds[0].b
 				if p.Kind == BlockIf && p.Controls[0].Op == OpIsNonNil && p.Succs[0].b == b {
-					if ptr := p.Controls[0].Args[0]; !nonNilValues[ptr.ID] {
-						nonNilValues[ptr.ID] = true
+					if ptr := p.Controls[0].Args[0]; nonNilValues[ptr.ID] == nil {
+						nonNilValues[ptr.ID] = ptr
 						work = append(work, bp{op: ClearPtr, ptr: ptr})
 					}
 				}
@@ -117,14 +120,11 @@ func nilcheckelim(f *Func) {
 			pendingLines.clear()
 
 			// Next, process values in the block.
-			i := 0
 			for _, v := range b.Values {
-				b.Values[i] = v
-				i++
 				switch v.Op {
 				case OpIsNonNil:
 					ptr := v.Args[0]
-					if nonNilValues[ptr.ID] {
+					if nonNilValues[ptr.ID] != nil {
 						if v.Pos.IsStmt() == src.PosIsStmt { // Boolean true is a terrible statement boundary.
 							pendingLines.add(v.Pos)
 							v.Pos = v.Pos.WithNotStmt()
@@ -135,7 +135,7 @@ func nilcheckelim(f *Func) {
 					}
 				case OpNilCheck:
 					ptr := v.Args[0]
-					if nonNilValues[ptr.ID] {
+					if nilCheck := nonNilValues[ptr.ID]; nilCheck != nil {
 						// This is a redundant implicit nil check.
 						// Logging in the style of the former compiler -- and omit line 1,
 						// which is usually in generated code.
@@ -145,14 +145,13 @@ func nilcheckelim(f *Func) {
 						if v.Pos.IsStmt() == src.PosIsStmt { // About to lose a statement boundary
 							pendingLines.add(v.Pos)
 						}
-						v.reset(OpUnknown)
-						f.freeValue(v)
-						i--
+						v.Op = OpCopy
+						v.SetArgs1(nilCheck)
 						continue
 					}
 					// Record the fact that we know ptr is non nil, and remember to
 					// undo that information when this dominator subtree is done.
-					nonNilValues[ptr.ID] = true
+					nonNilValues[ptr.ID] = v
 					work = append(work, bp{op: ClearPtr, ptr: ptr})
 					fallthrough // a non-eliminated nil check might be a good place for a statement boundary.
 				default:
@@ -163,7 +162,7 @@ func nilcheckelim(f *Func) {
 				}
 			}
 			// This reduces the lost statement count in "go" by 5 (out of 500 total).
-			for j := 0; j < i; j++ { // is this an ordering problem?
+			for j := range b.Values { // is this an ordering problem?
 				v := b.Values[j]
 				if v.Pos.IsStmt() != src.PosNotStmt && !isPoorStatementOp(v.Op) && pendingLines.contains(v.Pos) {
 					v.Pos = v.Pos.WithIsStmt()
@@ -174,7 +173,6 @@ func nilcheckelim(f *Func) {
 				b.Pos = b.Pos.WithIsStmt()
 				pendingLines.remove(b.Pos)
 			}
-			b.truncateValues(i)
 
 			// Add all dominated blocks to the work list.
 			for w := sdom[node.block.ID].child; w != nil; w = sdom[w.ID].sibling {
@@ -182,7 +180,7 @@ func nilcheckelim(f *Func) {
 			}
 
 		case ClearPtr:
-			nonNilValues[node.ptr.ID] = false
+			nonNilValues[node.ptr.ID] = nil
 			continue
 		}
 	}
diff --git a/src/cmd/compile/internal/ssa/opGen.go b/src/cmd/compile/internal/ssa/opGen.go
index 1480fcf45bf..e7caf9050c1 100644
--- a/src/cmd/compile/internal/ssa/opGen.go
+++ b/src/cmd/compile/internal/ssa/opGen.go
@@ -39373,9 +39373,10 @@ var opcodeTable = [...]opInfo{
 		generic: true,
 	},
 	{
-		name:    "NilCheck",
-		argLen:  2,
-		generic: true,
+		name:     "NilCheck",
+		argLen:   2,
+		nilCheck: true,
+		generic:  true,
 	},
 	{
 		name:      "GetG",
diff --git a/src/cmd/compile/internal/ssa/rewrite.go b/src/cmd/compile/internal/ssa/rewrite.go
index 5c7ed16f12b..1cfdc3e10d1 100644
--- a/src/cmd/compile/internal/ssa/rewrite.go
+++ b/src/cmd/compile/internal/ssa/rewrite.go
@@ -859,6 +859,9 @@ func disjoint(p1 *Value, n1 int64, p2 *Value, n2 int64) bool {
 			offset += base.AuxInt
 			base = base.Args[0]
 		}
+		if opcodeTable[base.Op].nilCheck {
+			base = base.Args[0]
+		}
 		return base, offset
 	}
 	p1, off1 := baseAndOffset(p1)
diff --git a/src/cmd/compile/internal/ssa/rewritegeneric.go b/src/cmd/compile/internal/ssa/rewritegeneric.go
index e5bd8bc36f7..574ac7a1a3a 100644
--- a/src/cmd/compile/internal/ssa/rewritegeneric.go
+++ b/src/cmd/compile/internal/ssa/rewritegeneric.go
@@ -18967,79 +18967,84 @@ func rewriteValuegeneric_OpNilCheck(v *Value) bool {
 	v_0 := v.Args[0]
 	b := v.Block
 	fe := b.Func.fe
-	// match: (NilCheck (GetG mem) mem)
-	// result: mem
+	// match: (NilCheck ptr:(GetG mem) mem)
+	// result: ptr
 	for {
-		if v_0.Op != OpGetG {
+		ptr := v_0
+		if ptr.Op != OpGetG {
 			break
 		}
-		mem := v_0.Args[0]
+		mem := ptr.Args[0]
 		if mem != v_1 {
 			break
 		}
-		v.copyOf(mem)
+		v.copyOf(ptr)
 		return true
 	}
-	// match: (NilCheck (SelectN [0] call:(StaticLECall _ _)) _)
+	// match: (NilCheck ptr:(SelectN [0] call:(StaticLECall _ _)) _)
 	// cond: isSameCall(call.Aux, "runtime.newobject") && warnRule(fe.Debug_checknil(), v, "removed nil check")
-	// result: (Invalid)
+	// result: ptr
 	for {
-		if v_0.Op != OpSelectN || auxIntToInt64(v_0.AuxInt) != 0 {
+		ptr := v_0
+		if ptr.Op != OpSelectN || auxIntToInt64(ptr.AuxInt) != 0 {
 			break
 		}
-		call := v_0.Args[0]
+		call := ptr.Args[0]
 		if call.Op != OpStaticLECall || len(call.Args) != 2 || !(isSameCall(call.Aux, "runtime.newobject") && warnRule(fe.Debug_checknil(), v, "removed nil check")) {
 			break
 		}
-		v.reset(OpInvalid)
+		v.copyOf(ptr)
 		return true
 	}
-	// match: (NilCheck (OffPtr (SelectN [0] call:(StaticLECall _ _))) _)
+	// match: (NilCheck ptr:(OffPtr (SelectN [0] call:(StaticLECall _ _))) _)
 	// cond: isSameCall(call.Aux, "runtime.newobject") && warnRule(fe.Debug_checknil(), v, "removed nil check")
-	// result: (Invalid)
+	// result: ptr
 	for {
-		if v_0.Op != OpOffPtr {
+		ptr := v_0
+		if ptr.Op != OpOffPtr {
 			break
 		}
-		v_0_0 := v_0.Args[0]
-		if v_0_0.Op != OpSelectN || auxIntToInt64(v_0_0.AuxInt) != 0 {
+		ptr_0 := ptr.Args[0]
+		if ptr_0.Op != OpSelectN || auxIntToInt64(ptr_0.AuxInt) != 0 {
 			break
 		}
-		call := v_0_0.Args[0]
+		call := ptr_0.Args[0]
 		if call.Op != OpStaticLECall || len(call.Args) != 2 || !(isSameCall(call.Aux, "runtime.newobject") && warnRule(fe.Debug_checknil(), v, "removed nil check")) {
 			break
 		}
-		v.reset(OpInvalid)
+		v.copyOf(ptr)
 		return true
 	}
-	// match: (NilCheck (Addr {_} (SB)) _)
-	// result: (Invalid)
+	// match: (NilCheck ptr:(Addr {_} (SB)) _)
+	// result: ptr
 	for {
-		if v_0.Op != OpAddr {
+		ptr := v_0
+		if ptr.Op != OpAddr {
 			break
 		}
-		v_0_0 := v_0.Args[0]
-		if v_0_0.Op != OpSB {
+		ptr_0 := ptr.Args[0]
+		if ptr_0.Op != OpSB {
 			break
 		}
-		v.reset(OpInvalid)
+		v.copyOf(ptr)
 		return true
 	}
-	// match: (NilCheck (Convert (Addr {_} (SB)) _) _)
-	// result: (Invalid)
+	// match: (NilCheck ptr:(Convert (Addr {_} (SB)) _) _)
+	// result: ptr
 	for {
-		if v_0.Op != OpConvert {
+		ptr := v_0
+		if ptr.Op != OpConvert {
 			break
 		}
-		v_0_0 := v_0.Args[0]
-		if v_0_0.Op != OpAddr {
+		ptr_0 := ptr.Args[0]
+		if ptr_0.Op != OpAddr {
 			break
 		}
-		v_0_0_0 := v_0_0.Args[0]
-		if v_0_0_0.Op != OpSB {
+		ptr_0_0 := ptr_0.Args[0]
+		if ptr_0_0.Op != OpSB {
 			break
 		}
-		v.reset(OpInvalid)
+		v.copyOf(ptr)
 		return true
 	}
 	return false
diff --git a/src/cmd/compile/internal/ssa/schedule.go b/src/cmd/compile/internal/ssa/schedule.go
index 19b98cc4b83..0a7425c0172 100644
--- a/src/cmd/compile/internal/ssa/schedule.go
+++ b/src/cmd/compile/internal/ssa/schedule.go
@@ -312,14 +312,21 @@ func schedule(f *Func) {
 	}
 
 	// Remove SPanchored now that we've scheduled.
+	// Also unlink nil checks now that ordering is assured
+	// between the nil check and the uses of the nil-checked pointer.
 	for _, b := range f.Blocks {
 		for _, v := range b.Values {
 			for i, a := range v.Args {
-				if a.Op == OpSPanchored {
+				if a.Op == OpSPanchored || opcodeTable[a.Op].nilCheck {
 					v.SetArg(i, a.Args[0])
 				}
 			}
 		}
+		for i, c := range b.ControlValues() {
+			if c.Op == OpSPanchored || opcodeTable[c.Op].nilCheck {
+				b.ReplaceControl(i, c.Args[0])
+			}
+		}
 	}
 	for _, b := range f.Blocks {
 		i := 0
@@ -332,6 +339,15 @@ func schedule(f *Func) {
 				v.resetArgs()
 				f.freeValue(v)
 			} else {
+				if opcodeTable[v.Op].nilCheck {
+					if v.Uses != 0 {
+						base.Fatalf("nilcheck still has %d uses", v.Uses)
+					}
+					// We can't delete the nil check, but we mark
+					// it as having void type so regalloc won't
+					// try to allocate a register for it.
+					v.Type = types.TypeVoid
+				}
 				b.Values[i] = v
 				i++
 			}
diff --git a/src/cmd/compile/internal/ssa/value.go b/src/cmd/compile/internal/ssa/value.go
index e89024b3c66..9b52da1c58a 100644
--- a/src/cmd/compile/internal/ssa/value.go
+++ b/src/cmd/compile/internal/ssa/value.go
@@ -552,7 +552,11 @@ func (v *Value) LackingPos() bool {
 // if its use count drops to 0.
 func (v *Value) removeable() bool {
 	if v.Type.IsVoid() {
-		// Void ops, like nil pointer checks, must stay.
+		// Void ops (inline marks), must stay.
+		return false
+	}
+	if opcodeTable[v.Op].nilCheck {
+		// Nil pointer checks must stay.
 		return false
 	}
 	if v.Type.IsMemory() {
diff --git a/src/cmd/compile/internal/ssagen/ssa.go b/src/cmd/compile/internal/ssagen/ssa.go
index 597a196ba8c..e994577c641 100644
--- a/src/cmd/compile/internal/ssagen/ssa.go
+++ b/src/cmd/compile/internal/ssagen/ssa.go
@@ -1991,7 +1991,8 @@ func (s *state) stmt(n ir.Node) {
 	case ir.OCHECKNIL:
 		n := n.(*ir.UnaryExpr)
 		p := s.expr(n.X)
-		s.nilCheck(p)
+		_ = s.nilCheck(p)
+		// TODO: check that throwing away the nilcheck result is ok.
 
 	case ir.OINLMARK:
 		n := n.(*ir.InlineMarkStmt)
@@ -5621,18 +5622,20 @@ func (s *state) exprPtr(n ir.Node, bounded bool, lineno src.XPos) *ssa.Value {
 		}
 		return p
 	}
-	s.nilCheck(p)
+	p = s.nilCheck(p)
 	return p
 }
 
 // nilCheck generates nil pointer checking code.
 // Used only for automatically inserted nil checks,
 // not for user code like 'x != nil'.
-func (s *state) nilCheck(ptr *ssa.Value) {
+// Returns a "definitely not nil" copy of x to ensure proper ordering
+// of the uses of the post-nilcheck pointer.
+func (s *state) nilCheck(ptr *ssa.Value) *ssa.Value {
 	if base.Debug.DisableNil != 0 || s.curfn.NilCheckDisabled() {
-		return
+		return ptr
 	}
-	s.newValue2(ssa.OpNilCheck, types.TypeVoid, ptr, s.mem())
+	return s.newValue2(ssa.OpNilCheck, ptr.Type, ptr, s.mem())
 }
 
 // boundsCheck generates bounds checking code. Checks if 0 <= idx <[=] len, branches to exit if not.
@@ -5984,8 +5987,8 @@ func (s *state) slice(v, i, j, k *ssa.Value, bounded bool) (p, l, c *ssa.Value)
 		if !t.Elem().IsArray() {
 			s.Fatalf("bad ptr to array in slice %v\n", t)
 		}
-		s.nilCheck(v)
-		ptr = s.newValue1(ssa.OpCopy, types.NewPtr(t.Elem().Elem()), v)
+		nv := s.nilCheck(v)
+		ptr = s.newValue1(ssa.OpCopy, types.NewPtr(t.Elem().Elem()), nv)
 		len = s.constInt(types.Types[types.TINT], t.Elem().NumElem())
 		cap = len
 	default:
diff --git a/test/fixedbugs/issue63657.go b/test/fixedbugs/issue63657.go
new file mode 100644
index 00000000000..e32a4a34fbb
--- /dev/null
+++ b/test/fixedbugs/issue63657.go
@@ -0,0 +1,48 @@
+// run
+
+// Copyright 2023 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.
+
+// Make sure address calculations don't float up before
+// the corresponding nil check.
+
+package main
+
+type T struct {
+	a, b int
+}
+
+//go:noinline
+func f(x *T, p *bool, n int) {
+	*p = n != 0
+	useStack(1000)
+	g(&x.b)
+}
+
+//go:noinline
+func g(p *int) {
+}
+
+func useStack(n int) {
+	if n == 0 {
+		return
+	}
+	useStack(n - 1)
+}
+
+func main() {
+	mustPanic(func() {
+		var b bool
+		f(nil, &b, 3)
+	})
+}
+
+func mustPanic(f func()) {
+	defer func() {
+		if recover() == nil {
+			panic("expected panic, got nil")
+		}
+	}()
+	f()
+}