cmd/compile: fold boolean NOT into branches

Gets rid of an EOR $1 instruction.

Change-Id: Ib032b0cee9ac484329c978af9b1305446f8d5dac
Reviewed-on: https://go-review.googlesource.com/c/go/+/721501
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Junyang Shao <shaojunyang@google.com>
Reviewed-by: Keith Randall <khr@google.com>

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

@@ -573,6 +573,8 @@
 (TBNZ [0] (GreaterThanF  cc) yes no) => (FGT cc yes no)
 (TBNZ [0] (GreaterEqualF cc) yes no) => (FGE cc yes no)
 
+(TB(Z|NZ) [0] (XORconst [1] x) yes no) => (TB(NZ|Z) [0] x yes no)
+
 ((EQ|NE|LT|LE|GT|GE) (CMPconst  [0] z:(AND        x y)) yes no) && z.Uses == 1 => ((EQ|NE|LT|LE|GT|GE) (TST                x y) yes no)
 ((EQ|NE|LT|LE|GT|GE) (CMPconst  [0] x:(ANDconst [c] y)) yes no) && x.Uses == 1 => ((EQ|NE|LT|LE|GT|GE) (TSTconst         [c] y) yes no)
 ((EQ|NE|LT|LE|GT|GE) (CMPWconst [0] z:(AND        x y)) yes no) && z.Uses == 1 => ((EQ|NE|LT|LE|GT|GE) (TSTW               x y) yes no)

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

@@ -25321,6 +25321,37 @@ func rewriteBlockARM64(b *Block) bool {
 			b.resetWithControl(BlockARM64FGE, cc)
 			return true
 		}
+		// match: (TBNZ [0] (XORconst [1] x) yes no)
+		// result: (TBZ [0] x yes no)
+		for b.Controls[0].Op == OpARM64XORconst {
+			v_0 := b.Controls[0]
+			if auxIntToInt64(v_0.AuxInt) != 1 {
+				break
+			}
+			x := v_0.Args[0]
+			if auxIntToInt64(b.AuxInt) != 0 {
+				break
+			}
+			b.resetWithControl(BlockARM64TBZ, x)
+			b.AuxInt = int64ToAuxInt(0)
+			return true
+		}
+	case BlockARM64TBZ:
+		// match: (TBZ [0] (XORconst [1] x) yes no)
+		// result: (TBNZ [0] x yes no)
+		for b.Controls[0].Op == OpARM64XORconst {
+			v_0 := b.Controls[0]
+			if auxIntToInt64(v_0.AuxInt) != 1 {
+				break
+			}
+			x := v_0.Args[0]
+			if auxIntToInt64(b.AuxInt) != 0 {
+				break
+			}
+			b.resetWithControl(BlockARM64TBNZ, x)
+			b.AuxInt = int64ToAuxInt(0)
+			return true
+		}
 	case BlockARM64UGE:
 		// match: (UGE (FlagConstant [fc]) yes no)
 		// cond: fc.uge()

test/codegen/bool.go

@@ -313,3 +313,18 @@ func constantWrite(b bool, p *bool) {
 		*p = b
 	}
 }
+
+func boolCompare1(p, q *bool) int {
+	// arm64:-"EOR [$]1"
+	if *p == *q {
+		return 5
+	}
+	return 7
+}
+func boolCompare2(p, q *bool) int {
+	// arm64:-"EOR [$]1"
+	if *p != *q {
+		return 5
+	}
+	return 7
+}