cgo: process DWARF info even when debug data is used for value

Always process the DWARF info, even when the const value is determined
using the debug data block. This ensures that the injected enum is
removed and future loads of the same constant do not trigger
inconsistent definitions.

Add tests for issues 2470 and 4054.
Fixes #4054.

R=golang-dev, fullung, dave, rsc, minux.ma
CC=golang-dev
https://golang.org/cl/6501101

misc/cgo/test/basic.go

@@ -14,6 +14,7 @@ package cgotest
 
 #define SHIFT(x, y)  ((x)<<(y))
 #define KILO SHIFT(1, 10)
+#define UINT32VAL 0xc008427bU
 
 enum E {
 	Enum1 = 1,
@@ -141,3 +142,12 @@ func benchCgoCall(b *testing.B) {
 		C.add(x, y)
 	}
 }
+
+// Issue 2470.
+func testUnsignedInt(t *testing.T) {
+	a := (int64)(C.UINT32VAL)
+	b := (int64)(0xc008427b)
+	if a != b {
+		t.Errorf("Incorrect unsigned int - got %x, want %x", a, b)
+	}
+}

misc/cgo/test/cgo_test.go

@@ -16,6 +16,7 @@ func TestEnum(t *testing.T)                { testEnum(t) }
 func TestAtol(t *testing.T)                { testAtol(t) }
 func TestErrno(t *testing.T)               { testErrno(t) }
 func TestMultipleAssign(t *testing.T)      { testMultipleAssign(t) }
+func TestUnsignedInt(t *testing.T)         { testUnsignedInt(t) }
 func TestCallback(t *testing.T)            { testCallback(t) }
 func TestCallbackGC(t *testing.T)          { testCallbackGC(t) }
 func TestCallbackPanic(t *testing.T)       { testCallbackPanic(t) }

misc/cgo/test/issue4054a.go

+// Copyright 2012 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
+
+/*
+typedef enum {
+	A = 0,
+	B,
+	C,
+	D,
+	E,
+	F,
+	G,
+	H,
+	I,
+	J,
+} issue4054a;
+*/
+import "C"
+
+var issue4054a = []int{C.A, C.B, C.C, C.D, C.E, C.F, C.G, C.H, C.I, C.J}

misc/cgo/test/issue4054b.go

+// Copyright 2012 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
+
+/*
+typedef enum {
+	A = 0,
+	B,
+	C,
+	D,
+	E,
+	F,
+	G,
+	H,
+	I,
+	J,
+} issue4054b;
+*/
+import "C"
+
+var issue4054b = []int{C.A, C.B, C.C, C.D, C.E, C.F, C.G, C.H, C.I, C.J}

src/cmd/cgo/gcc.go

@@ -616,10 +616,7 @@ func (p *Package) loadDWARF(f *File, names []*Name) {
 			n.FuncType = conv.FuncType(f, pos)
 		} else {
 			n.Type = conv.Type(types[i], pos)
-			// Prefer debug data over DWARF debug output, if we have it.
-			if n.Kind == "const" && i < len(enumVal) {
-				n.Const = fmt.Sprintf("%#x", enumVal[i])
-			} else if enums[i] != 0 && n.Type.EnumValues != nil {
+			if enums[i] != 0 && n.Type.EnumValues != nil {
 				k := fmt.Sprintf("__cgo_enum__%d", i)
 				n.Kind = "const"
 				n.Const = fmt.Sprintf("%#x", n.Type.EnumValues[k])
@@ -627,6 +624,10 @@ func (p *Package) loadDWARF(f *File, names []*Name) {
 				// equally in future loads of the same constant.
 				delete(n.Type.EnumValues, k)
 			}
+			// Prefer debug data over DWARF debug output, if we have it.
+			if n.Kind == "const" && i < len(enumVal) {
+				n.Const = fmt.Sprintf("%#x", enumVal[i])
+			}
 		}
 	}