debug/dwarf: correct name for clang-generated complex type

Fixes #8694.

LGTM=iant
R=iant
CC=golang-codereviews
https://golang.org/cl/143570043

misc/cgo/test/cgo_test.go

@@ -57,5 +57,6 @@ func Test7560(t *testing.T)                { test7560(t) }
 func Test5242(t *testing.T)                { test5242(t) }
 func Test8092(t *testing.T)                { test8092(t) }
 func Test7978(t *testing.T)                { test7978(t) }
+func Test8694(t *testing.T)                { test8694(t) }
 
 func BenchmarkCgoCall(b *testing.B) { benchCgoCall(b) }

misc/cgo/test/issue8694.go

+// Copyright 2014 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
+
+/*
+#include <complex.h>
+
+complex float complexFloatSquared(complex float a) { return a*a; }
+complex double complexDoubleSquared(complex double a) { return a*a; }
+*/
+import "C"
+
+import "testing"
+
+func test8694(t *testing.T) {
+	// Really just testing that this compiles, but check answer anyway.
+	x := complex64(2 + 3i)
+	x2 := x * x
+	cx2 := C.complexFloatSquared(x)
+	if cx2 != x2 {
+		t.Errorf("C.complexFloatSquared(%v) = %v, want %v", x, cx2, x2)
+	}
+
+	y := complex128(2 + 3i)
+	y2 := y * y
+	cy2 := C.complexDoubleSquared(y)
+	if cy2 != y2 {
+		t.Errorf("C.complexDoubleSquared(%v) = %v, want %v", y, cy2, y2)
+	}
+}

src/debug/dwarf/type.go

@@ -431,6 +431,17 @@ func (d *Data) readType(name string, r typeReader, off Offset, typeCache map[Off
 			typ = new(BoolType)
 		case encComplexFloat:
 			typ = new(ComplexType)
+			if name == "complex" {
+				// clang writes out 'complex' instead of 'complex float' or 'complex double'.
+				// clang also writes out a byte size that we can use to distinguish.
+				// See issue 8694.
+				switch byteSize, _ := e.Val(AttrByteSize).(int64); byteSize {
+				case 8:
+					name = "complex float"
+				case 16:
+					name = "complex double"
+				}
+			}
 		case encFloat:
 			typ = new(FloatType)
 		case encSigned: