cmd/compile: fix bug of conditional instructions on arm64

CL 302231 added some optimization rules with instructions CSETM, CSINC,
CSINV, and CSNEG, but did not deal with the situation where flag is
constant, resulting in some cases that could be more optimized cannot
be optimized, and the FlagConstant value is passed to codegen pass. This
CL adds these missing rules.

Fixes #45359

Change-Id: I700608cfb9a6a768a18d1fd5d374d7e92aa6f838
Reviewed-on: https://go-review.googlesource.com/c/go/+/307650
Reviewed-by: eric fang <[email protected]>
Reviewed-by: Keith Randall <[email protected]>
Reviewed-by: Cherry Zhang <[email protected]>
Reviewed-by: Alberto Donizetti <[email protected]>
Run-TryBot: eric fang <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Trust: eric fang <[email protected]>
Trust: Alberto Donizetti <[email protected]>

Author: eric fang

src/cmd/compile/internal/ssa/gen/ARM64.rules

@@ -1570,6 +1570,14 @@
 (CSEL [cc] _ y flag) && ccARM64Eval(cc, flag) < 0 => y
 (CSEL0 [cc] x flag) && ccARM64Eval(cc, flag) > 0 => x
 (CSEL0 [cc] _ flag) && ccARM64Eval(cc, flag) < 0 => (MOVDconst [0])
+(CSNEG [cc] x _ flag) && ccARM64Eval(cc, flag) > 0 => x
+(CSNEG [cc] _ y flag) && ccARM64Eval(cc, flag) < 0 => (NEG y)
+(CSINV [cc] x _ flag) && ccARM64Eval(cc, flag) > 0 => x
+(CSINV [cc] _ y flag) && ccARM64Eval(cc, flag) < 0 => (Not y)
+(CSINC [cc] x _ flag) && ccARM64Eval(cc, flag) > 0 => x
+(CSINC [cc] _ y flag) && ccARM64Eval(cc, flag) < 0 => (ADDconst [1] y)
+(CSETM [cc] flag) && ccARM64Eval(cc, flag) > 0 => (MOVDconst [-1])
+(CSETM [cc] flag) && ccARM64Eval(cc, flag) < 0 => (MOVDconst [0])
 
 // absorb flags back into boolean CSEL
 (CSEL [cc] x y (CMPWconst [0] boolval)) && cc == OpARM64NotEqual && flagArg(boolval) != nil =>

src/cmd/compile/internal/ssa/rewriteARM64.go

@@ -0,0 +1,20 @@
+// compile
+
+// Copyright 2021 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
+
+func f() {
+	var i, j int
+	var b bool
+	i = -(i &^ i)
+	for 1>>uint(i) == 0 {
+		_ = func() {
+			i, b = 0, true
+		}
+		_ = b
+		i %= j
+	}
+}