cmd/compile, cmd/cgo: align complex{64,128} like GCC

complex64 and complex128 are treated like [2]float32 and [2]float64,
so it makes sense to align them the same way.

Change-Id: Ic614bcdcc91b080aeb1ad1fed6fc15ba5a2971f8
Reviewed-on: https://go-review.googlesource.com/19800
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

misc/cgo/test/complex.go

+// Copyright 2016 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 cgotest
+
+/*
+struct {
+	float x;
+	_Complex float y;
+} cplxAlign = { 3.14, 2.17 };
+*/
+import "C"
+
+import "testing"
+
+func TestComplexAlign(t *testing.T) {
+	if C.cplxAlign.x != 3.14 {
+		t.Errorf("got %v, expected 3.14", C.cplxAlign.x)
+	}
+	if C.cplxAlign.y != 2.17 {
+		t.Errorf("got %v, expected 2.17", C.cplxAlign.y)
+	}
+}

src/cmd/cgo/gcc.go

@@ -1641,7 +1641,7 @@ func (c *typeConv) Type(dtype dwarf.Type, pos token.Pos) *Type {
 		case 16:
 			t.Go = c.complex128
 		}
-		if t.Align = t.Size; t.Align >= c.ptrSize {
+		if t.Align = t.Size / 2; t.Align >= c.ptrSize {
 			t.Align = c.ptrSize
 		}
 

src/cmd/cgo/out.go

@@ -1232,8 +1232,8 @@ var goTypes = map[string]*Type{
 	"uint64":     {Size: 8, Align: 8, C: c("GoUint64")},
 	"float32":    {Size: 4, Align: 4, C: c("GoFloat32")},
 	"float64":    {Size: 8, Align: 8, C: c("GoFloat64")},
-	"complex64":  {Size: 8, Align: 8, C: c("GoComplex64")},
-	"complex128": {Size: 16, Align: 16, C: c("GoComplex128")},
+	"complex64":  {Size: 8, Align: 4, C: c("GoComplex64")},
+	"complex128": {Size: 16, Align: 8, C: c("GoComplex128")},
 }
 
 // Map an ast type to a Type.

src/cmd/compile/internal/gc/align.go

@@ -169,10 +169,14 @@ func dowidth(t *Type) {
 	case TINT32, TUINT32, TFLOAT32:
 		w = 4
 
-	case TINT64, TUINT64, TFLOAT64, TCOMPLEX64:
+	case TINT64, TUINT64, TFLOAT64:
 		w = 8
 		t.Align = uint8(Widthreg)
 
+	case TCOMPLEX64:
+		w = 8
+		t.Align = 4
+
 	case TCOMPLEX128:
 		w = 16
 		t.Align = uint8(Widthreg)