cmd/compile: do not shapify when reading reshaping expr

Fixes #71184

Change-Id: I22e7ae5203311e86a90502bfe155b0597007887d
Reviewed-on: https://go-review.googlesource.com/c/go/+/641955
Auto-Submit: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Reviewed-by: Keith Randall <khr@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: David Chase <drchase@google.com>

src/cmd/compile/internal/noder/reader.go

@@ -49,6 +49,9 @@ type pkgReader struct {
 	// but bitwise inverted so we can detect if we're missing the entry
 	// or not.
 	newindex []index
+
+	// indicates whether the data is reading during reshaping.
+	reshaping bool
 }
 
 func newPkgReader(pr pkgbits.PkgDecoder) *pkgReader {
@@ -116,6 +119,10 @@ type reader struct {
 	// find parameters/results.
 	funarghack bool
 
+	// reshaping is used during reading exprReshape code, preventing
+	// the reader from shapifying the re-shaped type.
+	reshaping bool
+
 	// methodSym is the name of method's name, if reading a method.
 	// It's nil if reading a normal function or closure body.
 	methodSym *types.Sym
@@ -1007,7 +1014,7 @@ func (pr *pkgReader) objDictIdx(sym *types.Sym, idx index, implicits, explicits
 	// arguments.
 	for i, targ := range dict.targs {
 		basic := r.Bool()
-		if dict.shaped {
+		if dict.shaped && !pr.reshaping {
 			dict.targs[i] = shapify(targ, basic)
 		}
 	}
@@ -2445,7 +2452,10 @@ func (r *reader) expr() (res ir.Node) {
 
 	case exprReshape:
 		typ := r.typ()
+		old := r.reshaping
+		r.reshaping = true
 		x := r.expr()
+		r.reshaping = old
 
 		if types.IdenticalStrict(x.Type(), typ) {
 			return x
@@ -2568,7 +2578,10 @@ func (r *reader) funcInst(pos src.XPos) (wrapperFn, baseFn, dictPtr ir.Node) {
 		info := r.dict.subdicts[idx]
 		explicits := r.p.typListIdx(info.explicits, r.dict)
 
+		old := r.p.reshaping
+		r.p.reshaping = r.reshaping
 		baseFn = r.p.objIdx(info.idx, implicits, explicits, true).(*ir.Name)
+		r.p.reshaping = old
 
 		// TODO(mdempsky): Is there a more robust way to get the
 		// dictionary pointer type here?

test/fixedbugs/issue71184.go

@@ -0,0 +1,17 @@
+// compile
+
+// Copyright 2024 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 x
+
+func F[T int32]() {
+	_ = G[*[0]T]()[:]
+}
+
+func G[T any]() (v T) {
+	return
+}
+
+var _ = F[int32]