cmd/compile: optimize more pointer comparisons

The existing pointer comparison optimizations
don't include pointer arithmetic. Add them.

These rules trigger a few times in std cmd, while compiling:

time.Duration.String
cmd/go/internal/tlog.NodeHash
crypto/tls.ticketKeyFromBytes (3 times)
crypto/elliptic.(*p256Point).p256ScalarMult (15 times!)
crypto/elliptic.initTable

These weird comparisons occur when using the copy builtin,
which does a pointer comparison between src and dst.

This also happens to fix #32454, by optimizing enough
early on that all values can be eliminated.

Fixes #32454

Change-Id: I799d45743350bddd15a295dc1e12f8d03c11d1c6
Reviewed-on: https://go-review.googlesource.com/c/go/+/180940
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

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

@@ -1904,9 +1904,17 @@
 (EqPtr  x x) -> (ConstBool [1])
 (NeqPtr x x) -> (ConstBool [0])
 (EqPtr  (Addr {a} _) (Addr {b} _)) -> (ConstBool [b2i(a == b)])
+(EqPtr  (Addr {a} _) (OffPtr [o] (Addr {b} _))) -> (ConstBool [b2i(a == b && o == 0)])
+(EqPtr  (OffPtr [o1] (Addr {a} _)) (OffPtr [o2] (Addr {b} _))) -> (ConstBool [b2i(a == b && o1 == o2)])
 (NeqPtr (Addr {a} _) (Addr {b} _)) -> (ConstBool [b2i(a != b)])
+(NeqPtr (Addr {a} _) (OffPtr [o] (Addr {b} _))) -> (ConstBool [b2i(a != b || o != 0)])
+(NeqPtr (OffPtr [o1] (Addr {a} _)) (OffPtr [o2] (Addr {b} _))) -> (ConstBool [b2i(a != b || o1 != o2)])
 (EqPtr  (LocalAddr {a} _ _) (LocalAddr {b} _ _)) -> (ConstBool [b2i(a == b)])
+(EqPtr  (LocalAddr {a} _ _) (OffPtr [o] (LocalAddr {b} _ _))) -> (ConstBool [b2i(a == b && o == 0)])
+(EqPtr  (OffPtr [o1] (LocalAddr {a} _ _)) (OffPtr [o2] (LocalAddr {b} _ _))) -> (ConstBool [b2i(a == b && o1 == o2)])
 (NeqPtr (LocalAddr {a} _ _) (LocalAddr {b} _ _)) -> (ConstBool [b2i(a != b)])
+(NeqPtr (LocalAddr {a} _ _) (OffPtr [o] (LocalAddr {b} _ _))) -> (ConstBool [b2i(a != b || o != 0)])
+(NeqPtr (OffPtr [o1] (LocalAddr {a} _ _)) (OffPtr [o2] (LocalAddr {b} _ _))) -> (ConstBool [b2i(a != b || o1 != o2)])
 (EqPtr  (OffPtr [o1] p1) p2) && isSamePtr(p1, p2) -> (ConstBool [b2i(o1 == 0)])
 (NeqPtr (OffPtr [o1] p1) p2) && isSamePtr(p1, p2) -> (ConstBool [b2i(o1 != 0)])
 (EqPtr  (OffPtr [o1] p1) (OffPtr [o2] p2)) && isSamePtr(p1, p2) -> (ConstBool [b2i(o1 == o2)])
@@ -1915,7 +1923,13 @@
 (NeqPtr (Const(32|64) [c]) (Const(32|64) [d])) -> (ConstBool [b2i(c != d)])
 
 (EqPtr  (LocalAddr _ _) (Addr _)) -> (ConstBool [0])
+(EqPtr  (OffPtr (LocalAddr _ _)) (Addr _)) -> (ConstBool [0])
+(EqPtr  (LocalAddr _ _) (OffPtr (Addr _))) -> (ConstBool [0])
+(EqPtr  (OffPtr (LocalAddr _ _)) (OffPtr (Addr _))) -> (ConstBool [0])
 (NeqPtr (LocalAddr _ _) (Addr _)) -> (ConstBool [1])
+(NeqPtr (OffPtr (LocalAddr _ _)) (Addr _)) -> (ConstBool [1])
+(NeqPtr (LocalAddr _ _) (OffPtr (Addr _))) -> (ConstBool [1])
+(NeqPtr (OffPtr (LocalAddr _ _)) (OffPtr (Addr _))) -> (ConstBool [1])
 
 // Simplify address comparisons.
 (EqPtr  (AddPtr p1 o1) p2) && isSamePtr(p1, p2) -> (Not (IsNonNil o1))

test/fixedbugs/issue32454.go

+// compile
+
+// Copyright 2019 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 p
+
+type T struct {
+	s string
+	f float64
+}
+
+func f() {
+	var f float64
+	var st T
+	for {
+		switch &st.f {
+		case &f:
+			f = 1
+		}
+	}
+}