[release-branch.go1.16] cmd/compile: correct type of pointer differen…

…ce on RISCV64

Pointer comparison is lowered to the following on RISCV64

(EqPtr x y) => (SEQZ (SUB <x.Type> x y))

The difference of two pointers (the SUB) should not be pointer
type. Otherwise it can cause the GC to find a bad pointer.

Updates #51101.
Fixes #51198.

Change-Id: I7e73c2155c36ff403c032981a9aa9cccbfdf0f64
Reviewed-on: https://go-review.googlesource.com/c/go/+/385655
Trust: Cherry Mui <cherryyz@google.com>
Run-TryBot: Cherry Mui <cherryyz@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
(cherry picked from commit 1ed30ca)
Reviewed-on: https://go-review.googlesource.com/c/go/+/386475

src/cmd/compile/internal/ssa/gen/RISCV64.rules

@@ -249,15 +249,15 @@
 (Leq64F ...) => (FLED ...)
 (Leq32F ...) => (FLES ...)
 
-(EqPtr x y) => (SEQZ (SUB <x.Type> x y))
+(EqPtr x y) => (SEQZ (SUB <typ.Uintptr> x y))
 (Eq64  x y) => (SEQZ (SUB <x.Type> x y))
 (Eq32  x y) => (SEQZ (SUBW <x.Type> x y))
 (Eq16  x y) => (SEQZ (SUB <x.Type> (ZeroExt16to64 x) (ZeroExt16to64 y)))
 (Eq8   x y) => (SEQZ (SUB <x.Type> (ZeroExt8to64  x) (ZeroExt8to64  y)))
 (Eq64F ...) => (FEQD ...)
 (Eq32F ...) => (FEQS ...)
 
-(NeqPtr x y) => (SNEZ (SUB <x.Type> x y))
+(NeqPtr x y) => (SNEZ (SUB <typ.Uintptr> x y))
 (Neq64  x y) => (SNEZ (SUB <x.Type> x y))
 (Neq32  x y) => (SNEZ (SUBW <x.Type> x y))
 (Neq16  x y) => (SNEZ (SUB <x.Type> (ZeroExt16to64 x) (ZeroExt16to64 y)))

test/fixedbugs/issue51101.go

@@ -0,0 +1,36 @@
+// run
+
+// Copyright 2022 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.
+
+// Issue 51101: on RISCV64, difference of two pointers
+// was marked as pointer and crashes GC.
+
+package main
+
+var a, b int
+
+func main() {
+	F(&b, &a)
+}
+
+//go:noinline
+func F(a, b *int) bool {
+	x := a == b
+	G(x)
+	y := a != b
+	return y
+}
+
+//go:noinline
+func G(bool) {
+	grow([1000]int{20})
+}
+
+func grow(x [1000]int) {
+	if x[0] != 0 {
+		x[0]--
+		grow(x)
+	}
+}