cmd/compile: fold (NegNN (ConstNN ...))

Fix up and enable a few rules.
They trigger a handful of times in std,
despite the frontend handling.

Change-Id: I83378c057cbbc95a4f2b58cd8c36aec0e9dc547f
Reviewed-on: https://go-review.googlesource.com/37227
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

@@ -81,13 +81,12 @@
 (SignExt16to64 (Const16 [c])) -> (Const64 [int64( int16(c))])
 (SignExt32to64 (Const32 [c])) -> (Const64 [int64( int32(c))])
 
-// const negation is currently handled by frontend
-//(Neg8 (Const8 [c])) -> (Const8 [-c])
-//(Neg16 (Const16 [c])) -> (Const16 [-c])
-//(Neg32 (Const32 [c])) -> (Const32 [-c])
-//(Neg64 (Const64 [c])) -> (Const64 [-c])
-//(Neg32F (Const32F [c])) -> (Const32F [f2i(-i2f(c))])
-//(Neg64F (Const64F [c])) -> (Const64F [f2i(-i2f(c))])
+(Neg8   (Const8   [c])) -> (Const8   [int64( -int8(c))])
+(Neg16  (Const16  [c])) -> (Const16  [int64(-int16(c))])
+(Neg32  (Const32  [c])) -> (Const32  [int64(-int32(c))])
+(Neg64  (Const64  [c])) -> (Const64  [-c])
+(Neg32F (Const32F [c])) && i2f(c) != 0 -> (Const32F [f2i(-i2f(c))])
+(Neg64F (Const64F [c])) && i2f(c) != 0 -> (Const64F [f2i(-i2f(c))])
 
 (Add8   (Const8 [c])   (Const8 [d]))   -> (Const8  [int64(int8(c+d))])
 (Add16  (Const16 [c])  (Const16 [d]))  -> (Const16 [int64(int16(c+d))])

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

@@ -228,8 +228,12 @@ func rewriteValuegeneric(v *Value, config *Config) bool {
 		return rewriteValuegeneric_OpNeg16(v, config)
 	case OpNeg32:
 		return rewriteValuegeneric_OpNeg32(v, config)
+	case OpNeg32F:
+		return rewriteValuegeneric_OpNeg32F(v, config)
 	case OpNeg64:
 		return rewriteValuegeneric_OpNeg64(v, config)
+	case OpNeg64F:
+		return rewriteValuegeneric_OpNeg64F(v, config)
 	case OpNeg8:
 		return rewriteValuegeneric_OpNeg8(v, config)
 	case OpNeq16:
@@ -7676,6 +7680,19 @@ func rewriteValuegeneric_OpMul8(v *Value, config *Config) bool {
 func rewriteValuegeneric_OpNeg16(v *Value, config *Config) bool {
 	b := v.Block
 	_ = b
+	// match: (Neg16  (Const16  [c]))
+	// cond:
+	// result: (Const16  [int64(-int16(c))])
+	for {
+		v_0 := v.Args[0]
+		if v_0.Op != OpConst16 {
+			break
+		}
+		c := v_0.AuxInt
+		v.reset(OpConst16)
+		v.AuxInt = int64(-int16(c))
+		return true
+	}
 	// match: (Neg16 (Sub16 x y))
 	// cond:
 	// result: (Sub16 y x)
@@ -7696,6 +7713,19 @@ func rewriteValuegeneric_OpNeg16(v *Value, config *Config) bool {
 func rewriteValuegeneric_OpNeg32(v *Value, config *Config) bool {
 	b := v.Block
 	_ = b
+	// match: (Neg32  (Const32  [c]))
+	// cond:
+	// result: (Const32  [int64(-int32(c))])
+	for {
+		v_0 := v.Args[0]
+		if v_0.Op != OpConst32 {
+			break
+		}
+		c := v_0.AuxInt
+		v.reset(OpConst32)
+		v.AuxInt = int64(-int32(c))
+		return true
+	}
 	// match: (Neg32 (Sub32 x y))
 	// cond:
 	// result: (Sub32 y x)
@@ -7713,9 +7743,43 @@ func rewriteValuegeneric_OpNeg32(v *Value, config *Config) bool {
 	}
 	return false
 }
+func rewriteValuegeneric_OpNeg32F(v *Value, config *Config) bool {
+	b := v.Block
+	_ = b
+	// match: (Neg32F (Const32F [c]))
+	// cond: i2f(c) != 0
+	// result: (Const32F [f2i(-i2f(c))])
+	for {
+		v_0 := v.Args[0]
+		if v_0.Op != OpConst32F {
+			break
+		}
+		c := v_0.AuxInt
+		if !(i2f(c) != 0) {
+			break
+		}
+		v.reset(OpConst32F)
+		v.AuxInt = f2i(-i2f(c))
+		return true
+	}
+	return false
+}
 func rewriteValuegeneric_OpNeg64(v *Value, config *Config) bool {
 	b := v.Block
 	_ = b
+	// match: (Neg64  (Const64  [c]))
+	// cond:
+	// result: (Const64  [-c])
+	for {
+		v_0 := v.Args[0]
+		if v_0.Op != OpConst64 {
+			break
+		}
+		c := v_0.AuxInt
+		v.reset(OpConst64)
+		v.AuxInt = -c
+		return true
+	}
 	// match: (Neg64 (Sub64 x y))
 	// cond:
 	// result: (Sub64 y x)
@@ -7733,9 +7797,43 @@ func rewriteValuegeneric_OpNeg64(v *Value, config *Config) bool {
 	}
 	return false
 }
+func rewriteValuegeneric_OpNeg64F(v *Value, config *Config) bool {
+	b := v.Block
+	_ = b
+	// match: (Neg64F (Const64F [c]))
+	// cond: i2f(c) != 0
+	// result: (Const64F [f2i(-i2f(c))])
+	for {
+		v_0 := v.Args[0]
+		if v_0.Op != OpConst64F {
+			break
+		}
+		c := v_0.AuxInt
+		if !(i2f(c) != 0) {
+			break
+		}
+		v.reset(OpConst64F)
+		v.AuxInt = f2i(-i2f(c))
+		return true
+	}
+	return false
+}
 func rewriteValuegeneric_OpNeg8(v *Value, config *Config) bool {
 	b := v.Block
 	_ = b
+	// match: (Neg8   (Const8   [c]))
+	// cond:
+	// result: (Const8   [int64( -int8(c))])
+	for {
+		v_0 := v.Args[0]
+		if v_0.Op != OpConst8 {
+			break
+		}
+		c := v_0.AuxInt
+		v.reset(OpConst8)
+		v.AuxInt = int64(-int8(c))
+		return true
+	}
 	// match: (Neg8  (Sub8  x y))
 	// cond:
 	// result: (Sub8  y x)