[dev.ssa] cmd/compile/internal/ssa/gen: constant fold Neg*.

Change-Id: Id51e5c97e9653b764b809bf3424f1a6d31b6ffea
Reviewed-on: https://go-review.googlesource.com/19338
Run-TryBot: David Chase <drchase@google.com>
Reviewed-by: David Chase <drchase@google.com>

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

@@ -20,6 +20,11 @@
 // For now, the generated successors must be a permutation of the matched successors.
 
 // constant folding
+(Neg8 (Const8 [c])) -> (Const8 [-c])
+(Neg16 (Const16 [c])) -> (Const16 [-c])
+(Neg32 (Const32 [c])) -> (Const32 [-c])
+(Neg64 (Const64 [c])) -> (Const64 [-c])
+
 (Add8 (Const8 [c]) (Const8 [d])) -> (Const8 [c+d])
 (Add16 (Const16 [c]) (Const16 [d])) -> (Const16 [c+d])
 (Add32 (Const32 [c]) (Const32 [d])) -> (Const32 [c+d])

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

@@ -183,6 +183,14 @@ func rewriteValuegeneric(v *Value, config *Config) bool {
 		return rewriteValuegeneric_OpMul64(v, config)
 	case OpMul8:
 		return rewriteValuegeneric_OpMul8(v, config)
+	case OpNeg16:
+		return rewriteValuegeneric_OpNeg16(v, config)
+	case OpNeg32:
+		return rewriteValuegeneric_OpNeg32(v, config)
+	case OpNeg64:
+		return rewriteValuegeneric_OpNeg64(v, config)
+	case OpNeg8:
+		return rewriteValuegeneric_OpNeg8(v, config)
 	case OpNeq16:
 		return rewriteValuegeneric_OpNeq16(v, config)
 	case OpNeq32:
@@ -3428,6 +3436,74 @@ func rewriteValuegeneric_OpMul8(v *Value, config *Config) bool {
 	}
 	return false
 }
+func rewriteValuegeneric_OpNeg16(v *Value, config *Config) bool {
+	b := v.Block
+	_ = b
+	// match: (Neg16 (Const16 [c]))
+	// cond:
+	// result: (Const16 [-c])
+	for {
+		if v.Args[0].Op != OpConst16 {
+			break
+		}
+		c := v.Args[0].AuxInt
+		v.reset(OpConst16)
+		v.AuxInt = -c
+		return true
+	}
+	return false
+}
+func rewriteValuegeneric_OpNeg32(v *Value, config *Config) bool {
+	b := v.Block
+	_ = b
+	// match: (Neg32 (Const32 [c]))
+	// cond:
+	// result: (Const32 [-c])
+	for {
+		if v.Args[0].Op != OpConst32 {
+			break
+		}
+		c := v.Args[0].AuxInt
+		v.reset(OpConst32)
+		v.AuxInt = -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 {
+		if v.Args[0].Op != OpConst64 {
+			break
+		}
+		c := v.Args[0].AuxInt
+		v.reset(OpConst64)
+		v.AuxInt = -c
+		return true
+	}
+	return false
+}
+func rewriteValuegeneric_OpNeg8(v *Value, config *Config) bool {
+	b := v.Block
+	_ = b
+	// match: (Neg8 (Const8 [c]))
+	// cond:
+	// result: (Const8 [-c])
+	for {
+		if v.Args[0].Op != OpConst8 {
+			break
+		}
+		c := v.Args[0].AuxInt
+		v.reset(OpConst8)
+		v.AuxInt = -c
+		return true
+	}
+	return false
+}
 func rewriteValuegeneric_OpNeq16(v *Value, config *Config) bool {
 	b := v.Block
 	_ = b