cmd/compile: don't optimize away a panicing interface comparison

We can't do direct pointer comparisons if the type is not a
comparable type.

Fixes #76008

Change-Id: I1687acff21832d2c2e8f3b875e7b5ec125702ef3
Reviewed-on: https://go-review.googlesource.com/c/go/+/713840
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Keith Randall <khr@google.com>

2 files changed, 41 insertions, 4 deletions

diff --git a/src/cmd/compile/internal/ssa/rewrite.go b/src/cmd/compile/internal/ssa/rewrite.go
index 16c28e1ea4..2856ff2e43 100644
--- a/src/cmd/compile/internal/ssa/rewrite.go
+++ b/src/cmd/compile/internal/ssa/rewrite.go
@@ -2626,7 +2626,7 @@ func rewriteStructStore(v *Value) *Value {
 
 // isDirectType reports whether v represents a type
 // (a *runtime._type) whose value is stored directly in an
-// interface (i.e., is pointer or pointer-like).
+// interface (i.e., is pointer or pointer-like) and is comparable.
 func isDirectType(v *Value) bool {
 	return isDirectType1(v)
 }
@@ -2639,7 +2639,8 @@ func isDirectType1(v *Value) bool {
 	case OpAddr:
 		lsym := v.Aux.(*obj.LSym)
 		if ti := lsym.TypeInfo(); ti != nil {
-			return types.IsDirectIface(ti.Type.(*types.Type))
+			t := ti.Type.(*types.Type)
+			return types.IsDirectIface(t) && types.IsComparable(t)
 		}
 	}
 	return false
@@ -2656,7 +2657,7 @@ func isDirectType2(v *Value) bool {
 
 // isDirectIface reports whether v represents an itab
 // (a *runtime._itab) for a type whose value is stored directly
-// in an interface (i.e., is pointer or pointer-like).
+// in an interface (i.e., is pointer or pointer-like) and is comparable.
 func isDirectIface(v *Value) bool {
 	return isDirectIface1(v, 9)
 }
@@ -2672,7 +2673,8 @@ func isDirectIface1(v *Value, depth int) bool {
 	case OpAddr:
 		lsym := v.Aux.(*obj.LSym)
 		if ii := lsym.ItabInfo(); ii != nil {
-			return types.IsDirectIface(ii.Type.(*types.Type))
+			t := ii.Type.(*types.Type)
+			return types.IsDirectIface(t) && types.IsComparable(t)
 		}
 	case OpConstNil:
 		// We can treat this as direct, because if the itab is
diff --git a/test/fixedbugs/issue76008.go b/test/fixedbugs/issue76008.go
new file mode 100644
index 0000000000..bdf273bca1
--- /dev/null
+++ b/test/fixedbugs/issue76008.go
@@ -0,0 +1,35 @@
+// run
+
+// Copyright 2025 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 "runtime"
+
+func main() {
+	shouldPanic(func() {
+		g = any(func() {}) == any(func() {})
+	})
+	shouldPanic(func() {
+		g = any(map[int]int{}) == any(map[int]int{})
+	})
+	shouldPanic(func() {
+		g = any([]int{}) == any([]int{})
+	})
+}
+
+var g bool
+
+func shouldPanic(f func()) {
+	defer func() {
+		err := recover()
+		if err == nil {
+			_, _, line, _ := runtime.Caller(2)
+			println("did not panic at line", line+1)
+		}
+	}()
+
+	f()
+}