From: Michael Munday <mike.munday@lowrisc.org>
Date: Wed, 27 Aug 2025 22:07:36 +0000 (+0100)
Subject: cmd/compile: remove sign extension before MULW on riscv64
X-Git-Tag: go1.26rc1~991
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=27ce6e4e26;p=gostls13.git

cmd/compile: remove sign extension before MULW on riscv64

These sign extensions aren't necessary.

Change-Id: Id68ea596a18b30949d4605b2885f02e49e42d8e1
Reviewed-on: https://go-review.googlesource.com/c/go/+/699595
Reviewed-by: Keith Randall <khr@golang.org>
Auto-Submit: Keith Randall <khr@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
---

diff --git a/src/cmd/compile/internal/ssa/_gen/RISCV64.rules b/src/cmd/compile/internal/ssa/_gen/RISCV64.rules
index 9d79fc34e8..151f3412ce 100644
--- a/src/cmd/compile/internal/ssa/_gen/RISCV64.rules
+++ b/src/cmd/compile/internal/ssa/_gen/RISCV64.rules
@@ -12,9 +12,7 @@
 (Mul64 ...) => (MUL  ...)
 (Mul64uhilo ...) => (LoweredMuluhilo ...)
 (Mul64uover ...) => (LoweredMuluover ...)
-(Mul32 ...) => (MULW ...)
-(Mul16 x y) => (MULW (SignExt16to32 x) (SignExt16to32 y))
-(Mul8 x y)  => (MULW (SignExt8to32 x)  (SignExt8to32 y))
+(Mul(32|16|8) ...) => (MULW ...)
 (Mul(64|32)F ...) => (FMUL(D|S) ...)
 
 (Div(64|32)F ...) => (FDIV(D|S) ...)
diff --git a/src/cmd/compile/internal/ssa/rewriteRISCV64.go b/src/cmd/compile/internal/ssa/rewriteRISCV64.go
index c78ae89561..1e80669672 100644
--- a/src/cmd/compile/internal/ssa/rewriteRISCV64.go
+++ b/src/cmd/compile/internal/ssa/rewriteRISCV64.go
@@ -405,7 +405,8 @@ func rewriteValueRISCV64(v *Value) bool {
 	case OpMove:
 		return rewriteValueRISCV64_OpMove(v)
 	case OpMul16:
-		return rewriteValueRISCV64_OpMul16(v)
+		v.Op = OpRISCV64MULW
+		return true
 	case OpMul32:
 		v.Op = OpRISCV64MULW
 		return true
@@ -425,7 +426,8 @@ func rewriteValueRISCV64(v *Value) bool {
 		v.Op = OpRISCV64LoweredMuluover
 		return true
 	case OpMul8:
-		return rewriteValueRISCV64_OpMul8(v)
+		v.Op = OpRISCV64MULW
+		return true
 	case OpNeg16:
 		v.Op = OpRISCV64NEG
 		return true
@@ -3255,44 +3257,6 @@ func rewriteValueRISCV64_OpMove(v *Value) bool {
 	}
 	return false
 }
-func rewriteValueRISCV64_OpMul16(v *Value) bool {
-	v_1 := v.Args[1]
-	v_0 := v.Args[0]
-	b := v.Block
-	typ := &b.Func.Config.Types
-	// match: (Mul16 x y)
-	// result: (MULW (SignExt16to32 x) (SignExt16to32 y))
-	for {
-		x := v_0
-		y := v_1
-		v.reset(OpRISCV64MULW)
-		v0 := b.NewValue0(v.Pos, OpSignExt16to32, typ.Int32)
-		v0.AddArg(x)
-		v1 := b.NewValue0(v.Pos, OpSignExt16to32, typ.Int32)
-		v1.AddArg(y)
-		v.AddArg2(v0, v1)
-		return true
-	}
-}
-func rewriteValueRISCV64_OpMul8(v *Value) bool {
-	v_1 := v.Args[1]
-	v_0 := v.Args[0]
-	b := v.Block
-	typ := &b.Func.Config.Types
-	// match: (Mul8 x y)
-	// result: (MULW (SignExt8to32 x) (SignExt8to32 y))
-	for {
-		x := v_0
-		y := v_1
-		v.reset(OpRISCV64MULW)
-		v0 := b.NewValue0(v.Pos, OpSignExt8to32, typ.Int32)
-		v0.AddArg(x)
-		v1 := b.NewValue0(v.Pos, OpSignExt8to32, typ.Int32)
-		v1.AddArg(y)
-		v.AddArg2(v0, v1)
-		return true
-	}
-}
 func rewriteValueRISCV64_OpNeq16(v *Value) bool {
 	v_1 := v.Args[1]
 	v_0 := v.Args[0]