[release-branch.go1.26] cmd/compile: ensure StructMake/ArrayMake1 of direct interfaces are unwrapped

Ensures that deeply nested structs that have the underlying shape
of a pointer get unwrapped properly.

Update #77536

Change-Id: I004f424d2c62ec7026281daded9b3d96c021e2e1
Reviewed-on: https://go-review.googlesource.com/c/go/+/747760
Reviewed-by: Mark Freeman <markfreeman@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: David Chase <drchase@google.com>
(cherry picked from commit 1aa534dbb8970b86b0f4059b7665e3505d145e25)
Reviewed-on: https://go-review.googlesource.com/c/go/+/749460

3 files changed, 26 insertions, 1 deletions

diff --git a/src/cmd/compile/internal/ssa/_gen/dec.rules b/src/cmd/compile/internal/ssa/_gen/dec.rules
index fce0026211..a04a7cd5f8 100644
--- a/src/cmd/compile/internal/ssa/_gen/dec.rules
+++ b/src/cmd/compile/internal/ssa/_gen/dec.rules
@@ -80,7 +80,9 @@
 
 // interface ops
 (ITab (IMake itab _)) => itab
-(IData (IMake _ data)) => data
+(IData (IMake _ data)) && data.Op != OpStructMake && data.Op != OpArrayMake1 => data
+// Note: the conditional on data.Op ensures that StructMake/ArrayMake1 ops are
+// unwrapped before the IMake is thrown away. See issue 77534.
 
 (Load <t> ptr mem) && t.IsInterface() =>
   (IMake
diff --git a/src/cmd/compile/internal/ssa/rewritedec.go b/src/cmd/compile/internal/ssa/rewritedec.go
index c45034ead0..1e5c19cd23 100644
--- a/src/cmd/compile/internal/ssa/rewritedec.go
+++ b/src/cmd/compile/internal/ssa/rewritedec.go
@@ -242,12 +242,16 @@ func rewriteValuedec_OpIData(v *Value) bool {
 	config := b.Func.Config
 	typ := &b.Func.Config.Types
 	// match: (IData (IMake _ data))
+	// cond: data.Op != OpStructMake && data.Op != OpArrayMake1
 	// result: data
 	for {
 		if v_0.Op != OpIMake {
 			break
 		}
 		data := v_0.Args[1]
+		if !(data.Op != OpStructMake && data.Op != OpArrayMake1) {
+			break
+		}
 		v.copyOf(data)
 		return true
 	}
diff --git a/test/fixedbugs/issue77534.go b/test/fixedbugs/issue77534.go
index ab4f922308..77a6e616e6 100644
--- a/test/fixedbugs/issue77534.go
+++ b/test/fixedbugs/issue77534.go
@@ -34,3 +34,22 @@ func f3(p, x, y *T, b bool) {
 func f4(i any) T {
 	return i.(T)
 }
+
+type Inner struct {
+	a struct{}
+	p *byte
+}
+
+type Outer struct {
+	inner Inner
+}
+
+func f5(o1, o2 Outer, c bool) Outer {
+	var i any
+	if c {
+		i = o1
+	} else {
+		i = o2
+	}
+	return i.(Outer)
+}