cmd/compile: fixed which-result confusion in presence of 0-width types

A function returning multiple results, some of them zero-width,
will have more than one result present at an offset.  Be sure
that offset AND type match.

Includes test.

Change-Id: I3eb1f56116d989b4e73f533fefabb1bf554c901b
Reviewed-on: https://go-review.googlesource.com/c/go/+/297169
Trust: David Chase <drchase@google.com>
Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Jeremy Faller <jeremy@golang.org>

diff --git a/src/cmd/compile/internal/ssa/op.go b/src/cmd/compile/internal/ssa/op.go
index 6949bdca31feb31a5fc1aed8291addfa07d458b5..ece274b0834f1a86b95d15d7c45ca318a4f64e07 100644 (file)
--- a/src/cmd/compile/internal/ssa/op.go
+++ b/src/cmd/compile/internal/ssa/op.go
@@ -86,12 +86,15 @@ type AuxCall struct {
        abiInfo *abi.ABIParamResultInfo // TODO remove fields above redundant with this information.
 }
 
-// ResultForOffset returns the index of the result at a particular offset among the results
+// ResultForOffsetAndType returns the index of a t-typed result at *A* particular offset among the results.
+// An arbitrary number of zero-width-typed results may reside at the same offset with a single not-zero-width
+// typed result, but the ones with the same type are all indistinguishable so it doesn't matter "which one"
+// is obtained.
 // This does not include the mem result for the call opcode.
-func (a *AuxCall) ResultForOffset(offset int64) int64 {
+func (a *AuxCall) ResultForOffsetAndType(offset int64, t *types.Type) int64 {
        which := int64(-1)
        for i := int64(0); i < a.NResults(); i++ { // note aux NResults does not include mem result.
-               if a.OffsetOfResult(i) == offset {
+               if a.OffsetOfResult(i) == offset && a.TypeOfResult(i) == t {
                        which = i
                        break
                }

diff --git a/src/cmd/compile/internal/ssagen/ssa.go b/src/cmd/compile/internal/ssagen/ssa.go
index ba00b9c7f6e3428a1579889318801ece028091e5..865630dd3ec349addb58bc52afbeb3b5d6207273 100644 (file)
--- a/src/cmd/compile/internal/ssagen/ssa.go
+++ b/src/cmd/compile/internal/ssagen/ssa.go
@@ -2909,7 +2909,7 @@ func (s *state) expr(n ir.Node) *ssa.Value {
                        addr := s.constOffPtrSP(types.NewPtr(n.Type()), n.Offset)
                        return s.rawLoad(n.Type(), addr)
                }
-               which := s.prevCall.Aux.(*ssa.AuxCall).ResultForOffset(n.Offset)
+               which := s.prevCall.Aux.(*ssa.AuxCall).ResultForOffsetAndType(n.Offset, n.Type())
                if which == -1 {
                        // Do the old thing // TODO: Panic instead.
                        addr := s.constOffPtrSP(types.NewPtr(n.Type()), n.Offset)
@@ -5119,7 +5119,7 @@ func (s *state) addr(n ir.Node) *ssa.Value {
                if s.prevCall == nil || s.prevCall.Op != ssa.OpStaticLECall && s.prevCall.Op != ssa.OpInterLECall && s.prevCall.Op != ssa.OpClosureLECall {
                        return s.constOffPtrSP(t, n.Offset)
                }
-               which := s.prevCall.Aux.(*ssa.AuxCall).ResultForOffset(n.Offset)
+               which := s.prevCall.Aux.(*ssa.AuxCall).ResultForOffsetAndType(n.Offset, n.Type())
                if which == -1 {
                        // Do the old thing // TODO: Panic instead.
                        return s.constOffPtrSP(t, n.Offset)

diff --git a/test/abi/f_ret_z_not.go b/test/abi/f_ret_z_not.go
new file mode 100644 (file)
index 0000000..b072aea
--- /dev/null
+++ b/test/abi/f_ret_z_not.go
@@ -0,0 +1,33 @@
+// run
+
+// Copyright 2021 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 "fmt"
+
+type Z struct {
+}
+
+type NZ struct {
+       x, y int
+}
+
+//go:noinline
+func f(x,y int) (Z,NZ,Z) {
+       var z Z
+       return z,NZ{x,y},z
+}
+
+//go:noinline
+func g() (Z,NZ,Z) {
+       a,b,c := f(3,4)
+       return c,b,a
+}
+
+func main() {
+       _,b,_ := g()
+       fmt.Println(b.x+b.y)
+}

diff --git a/test/abi/f_ret_z_not.out b/test/abi/f_ret_z_not.out
new file mode 100644 (file)
index 0000000..7f8f011
--- /dev/null
+++ b/test/abi/f_ret_z_not.out
@@ -0,0 +1 @@
+7