cmd/compile: constant fold !true and !false

Constant fold Not of boolean constants.

Noticed while working on #23504.

Change-Id: I965705154ee7348a1a159fad4e029b922d3171b3
Reviewed-on: https://go-review.googlesource.com/88956
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Martin Möhrmann <moehrmann@google.com>

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

@@ -150,6 +150,8 @@
 (Div32F (Const32F [c]) (Const32F [d])) -> (Const32F [f2i(float64(i2f32(c) / i2f32(d)))])
 (Div64F (Const64F [c]) (Const64F [d])) -> (Const64F [f2i(i2f(c) / i2f(d))])
 
+(Not (ConstBool [c])) -> (ConstBool [1-c])
+
 // Convert x * 1 to x.
 (Mul8  (Const8  [1]) x) -> x
 (Mul16 (Const16 [1]) x) -> x

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

@@ -17715,6 +17715,19 @@ func rewriteValuegeneric_OpNilCheck_0(v *Value) bool {
 	return false
 }
 func rewriteValuegeneric_OpNot_0(v *Value) bool {
+	// match: (Not (ConstBool [c]))
+	// cond:
+	// result: (ConstBool [1-c])
+	for {
+		v_0 := v.Args[0]
+		if v_0.Op != OpConstBool {
+			break
+		}
+		c := v_0.AuxInt
+		v.reset(OpConstBool)
+		v.AuxInt = 1 - c
+		return true
+	}
 	// match: (Not (Eq64 x y))
 	// cond:
 	// result: (Neq64 x y)
@@ -17859,6 +17872,9 @@ func rewriteValuegeneric_OpNot_0(v *Value) bool {
 		v.AddArg(y)
 		return true
 	}
+	return false
+}
+func rewriteValuegeneric_OpNot_10(v *Value) bool {
 	// match: (Not (NeqB x y))
 	// cond:
 	// result: (EqB  x y)
@@ -17875,9 +17891,6 @@ func rewriteValuegeneric_OpNot_0(v *Value) bool {
 		v.AddArg(y)
 		return true
 	}
-	return false
-}
-func rewriteValuegeneric_OpNot_10(v *Value) bool {
 	// match: (Not (Greater64 x y))
 	// cond:
 	// result: (Leq64 x y)
@@ -18022,6 +18035,9 @@ func rewriteValuegeneric_OpNot_10(v *Value) bool {
 		v.AddArg(y)
 		return true
 	}
+	return false
+}
+func rewriteValuegeneric_OpNot_20(v *Value) bool {
 	// match: (Not (Geq32 x y))
 	// cond:
 	// result: (Less32 x y)
@@ -18038,9 +18054,6 @@ func rewriteValuegeneric_OpNot_10(v *Value) bool {
 		v.AddArg(y)
 		return true
 	}
-	return false
-}
-func rewriteValuegeneric_OpNot_20(v *Value) bool {
 	// match: (Not (Geq16 x y))
 	// cond:
 	// result: (Less16 x y)
@@ -18185,6 +18198,9 @@ func rewriteValuegeneric_OpNot_20(v *Value) bool {
 		v.AddArg(y)
 		return true
 	}
+	return false
+}
+func rewriteValuegeneric_OpNot_30(v *Value) bool {
 	// match: (Not (Less8 x y))
 	// cond:
 	// result: (Geq8  x y)
@@ -18201,9 +18217,6 @@ func rewriteValuegeneric_OpNot_20(v *Value) bool {
 		v.AddArg(y)
 		return true
 	}
-	return false
-}
-func rewriteValuegeneric_OpNot_30(v *Value) bool {
 	// match: (Not (Less64U x y))
 	// cond:
 	// result: (Geq64U x y)
@@ -18348,6 +18361,9 @@ func rewriteValuegeneric_OpNot_30(v *Value) bool {
 		v.AddArg(y)
 		return true
 	}
+	return false
+}
+func rewriteValuegeneric_OpNot_40(v *Value) bool {
 	// match: (Not (Leq32U x y))
 	// cond:
 	// result: (Greater32U x y)
@@ -18364,9 +18380,6 @@ func rewriteValuegeneric_OpNot_30(v *Value) bool {
 		v.AddArg(y)
 		return true
 	}
-	return false
-}
-func rewriteValuegeneric_OpNot_40(v *Value) bool {
 	// match: (Not (Leq16U x y))
 	// cond:
 	// result: (Greater16U x y)