cmd/compile/internal/typebits: relax alignment check

Now we have 8-byte alignment types on 32-bit system, so in some rare
case, e.g, generated wrapper for embedded interface, the function
argument may need more than 4 byte alignment. We could pad somehow, but
this is a rare case which makes it hard to ensure that we've got it right.

So relaxing the check for argument and return value region of the stack.

Fixes #54991

Change-Id: I34986e17a920254392a39439ad3dcb323da2ea8d
Reviewed-on: https://go-review.googlesource.com/c/go/+/431098
Reviewed-by: Keith Randall <khr@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Run-TryBot: Cuong Manh Le <cuong.manhle.vn@gmail.com>
Auto-Submit: Keith Randall <khr@golang.org>
Reviewed-by: Keith Randall <khr@google.com>

src/cmd/compile/internal/liveness/plive.go

@@ -425,7 +425,7 @@ func (lv *liveness) pointerMap(liveout bitvec.BitVec, vars []*ir.Name, args, loc
 				if node.FrameOffset() < 0 {
 					lv.f.Fatalf("Node %v has frameoffset %d\n", node.Sym().Name, node.FrameOffset())
 				}
-				typebits.Set(node.Type(), node.FrameOffset(), args)
+				typebits.SetNoCheck(node.Type(), node.FrameOffset(), args)
 				break
 			}
 			fallthrough // PPARAMOUT in registers acts memory-allocates like an AUTO
@@ -1498,7 +1498,7 @@ func WriteFuncMap(fn *ir.Func, abiInfo *abi.ABIParamResultInfo) {
 	bv := bitvec.New(int32(nptr) * 2)
 
 	for _, p := range abiInfo.InParams() {
-		typebits.Set(p.Type, p.FrameOffset(abiInfo), bv)
+		typebits.SetNoCheck(p.Type, p.FrameOffset(abiInfo), bv)
 	}
 
 	nbitmap := 1
@@ -1513,7 +1513,7 @@ func WriteFuncMap(fn *ir.Func, abiInfo *abi.ABIParamResultInfo) {
 	if fn.Type().NumResults() > 0 {
 		for _, p := range abiInfo.OutParams() {
 			if len(p.Registers) == 0 {
-				typebits.Set(p.Type, p.FrameOffset(abiInfo), bv)
+				typebits.SetNoCheck(p.Type, p.FrameOffset(abiInfo), bv)
 			}
 		}
 		off = objw.BitVec(lsym, off, bv)

src/cmd/compile/internal/typebits/typebits.go

@@ -14,7 +14,16 @@ import (
 // the first run and then simply copied into bv at the correct offset
 // on future calls with the same type t.
 func Set(t *types.Type, off int64, bv bitvec.BitVec) {
-	if uint8(t.Alignment()) > 0 && off&int64(uint8(t.Alignment())-1) != 0 {
+	set(t, off, bv, false)
+}
+
+// SetNoCheck is like Set, but do not check for alignment.
+func SetNoCheck(t *types.Type, off int64, bv bitvec.BitVec) {
+	set(t, off, bv, true)
+}
+
+func set(t *types.Type, off int64, bv bitvec.BitVec, skip bool) {
+	if !skip && uint8(t.Alignment()) > 0 && off&int64(uint8(t.Alignment())-1) != 0 {
 		base.Fatalf("typebits.Set: invalid initial alignment: type %v has alignment %d, but offset is %v", t, uint8(t.Alignment()), off)
 	}
 	if !t.HasPointers() {
@@ -72,13 +81,13 @@ func Set(t *types.Type, off int64, bv bitvec.BitVec) {
 			break
 		}
 		for i := int64(0); i < t.NumElem(); i++ {
-			Set(elt, off, bv)
+			set(elt, off, bv, skip)
 			off += elt.Size()
 		}
 
 	case types.TSTRUCT:
 		for _, f := range t.Fields().Slice() {
-			Set(f.Type, off+f.Offset, bv)
+			set(f.Type, off+f.Offset, bv, skip)
 		}
 
 	default:

test/fixedbugs/issue54991.go

@@ -0,0 +1,29 @@
+// compile
+
+// Copyright 2022 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 p
+
+import (
+	"sync/atomic"
+)
+
+type I interface {
+	M()
+}
+
+type S struct{}
+
+func (*S) M() {}
+
+type T struct {
+	I
+	x atomic.Int64
+}
+
+func F() {
+	t := &T{I: &S{}}
+	t.M()
+}