cmd/compile: fix constant pointer comparison failure

Previously, constant pointer-typed expressions could use either Mpint
or NilVal as their Val depending on their construction, but const.go
expects each type to have a single corresponding Val kind.

This CL changes pointer-typed expressions to exclusively use Mpint.

Fixes #21221.

Change-Id: I6ba36c9b11eb19a68306f0b296acb11a8c254c41
Reviewed-on: https://go-review.googlesource.com/105315
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>

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

@@ -319,7 +319,8 @@ func (p *importer) pkg() *types.Pkg {
 }
 
 func idealType(typ *types.Type) *types.Type {
-	if typ.IsUntyped() {
+	switch typ {
+	case types.Idealint, types.Idealrune, types.Idealfloat, types.Idealcomplex:
 		// canonicalize ideal types
 		typ = types.Types[TIDEAL]
 	}
@@ -795,8 +796,12 @@ func (p *importer) value(typ *types.Type) (x Val) {
 	case floatTag:
 		f := newMpflt()
 		p.float(f)
-		if typ == types.Idealint || typ.IsInteger() {
+		if typ == types.Idealint || typ.IsInteger() || typ.IsPtr() || typ.IsUnsafePtr() {
 			// uncommon case: large int encoded as float
+			//
+			// This happens for unsigned typed integers
+			// and (on 64-bit platforms) pointers because
+			// of values in the range [2^63, 2^64).
 			u := new(Mpint)
 			u.SetFloat(f)
 			x.U = u
@@ -929,18 +934,7 @@ func (p *importer) node() *Node {
 		pos := p.pos()
 		typ := p.typ()
 		n := npos(pos, nodlit(p.value(typ)))
-		if !typ.IsUntyped() {
-			// Type-checking simplifies unsafe.Pointer(uintptr(c))
-			// to unsafe.Pointer(c) which then cannot type-checked
-			// again. Re-introduce explicit uintptr(c) conversion.
-			// (issue 16317).
-			if typ.IsUnsafePtr() {
-				n = nodl(pos, OCONV, n, nil)
-				n.Type = types.Types[TUINTPTR]
-			}
-			n = nodl(pos, OCONV, n, nil)
-			n.Type = typ
-		}
+		n.Type = idealType(typ)
 		return n
 
 	case ONAME:

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

@@ -331,26 +331,11 @@ func convlit1(n *Node, t *types.Type, explicit bool, reuse canReuseNode) *Node {
 		case TARRAY:
 			goto bad
 
-		case TPTR32,
-			TPTR64,
-			TINTER,
-			TMAP,
-			TCHAN,
-			TFUNC,
-			TSLICE,
-			TUNSAFEPTR:
-			break
+		case TPTR32, TPTR64, TUNSAFEPTR:
+			n.SetVal(Val{new(Mpint)})
 
-		// A nil literal may be converted to uintptr
-		// if it is an unsafe.Pointer
-		case TUINTPTR:
-			if n.Type.Etype == TUNSAFEPTR {
-				i := new(Mpint)
-				i.SetInt64(0)
-				n.SetVal(Val{i})
-			} else {
-				goto bad
-			}
+		case TCHAN, TFUNC, TINTER, TMAP, TSLICE:
+			break
 		}
 
 	case CTSTR, CTBOOL:

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

@@ -145,7 +145,7 @@ func importconst(pos src.XPos, pkg *types.Pkg, s *types.Sym, t *types.Type, val
 	}
 
 	n := npos(pos, nodlit(val))
-	n = convlit1(n, t, false, reuseOK)
+	n.Type = t
 	n.Sym = s
 	declare(n, PEXTERN)
 

test/const1.go

@@ -90,5 +90,5 @@ func main() {
 const ptr = nil // ERROR "const.*nil"
 const _ = string([]byte(nil)) // ERROR "is not a? ?constant"
 const _ = uintptr(unsafe.Pointer((*int)(nil))) // ERROR "is not a? ?constant"
-const _ = unsafe.Pointer((*int)(nil)) // ERROR "cannot be nil|invalid constant type"
-const _ = (*int)(nil) // ERROR "cannot be nil|invalid constant type"
+const _ = unsafe.Pointer((*int)(nil)) // ERROR "cannot be nil|invalid constant type|is not a constant"
+const _ = (*int)(nil) // ERROR "cannot be nil|invalid constant type|is not a constant"

test/fixedbugs/issue21221.go

+// run
+
+// Copyright 2018 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 "unsafe"
+
+func main() {
+	if unsafe.Pointer(uintptr(0)) != unsafe.Pointer(nil) {
+		panic("fail")
+	}
+	if (*int)(unsafe.Pointer(uintptr(0))) != (*int)(nil) {
+		panic("fail")
+	}
+}