From e1a12c781f55da85a30fd63471f8adcba908acd2 Mon Sep 17 00:00:00 2001
From: Keith Randall <khr@golang.org>
Date: Mon, 17 Nov 2025 12:47:04 -0800
Subject: [PATCH] cmd/compile: use 32x32->64 multiplies on arm64

Gets rid of some sign extensions.

Change-Id: Ie67ef36b4ca1cd1a2cd9fa5d84578db553578a22
Reviewed-on: https://go-review.googlesource.com/c/go/+/721241
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 |  4 ++
 src/cmd/compile/internal/ssa/rewriteARM64.go  | 48 +++++++++++++++++++
 test/codegen/arithmetic.go                    |  9 ++++
 3 files changed, 61 insertions(+)

diff --git a/src/cmd/compile/internal/ssa/_gen/ARM64.rules b/src/cmd/compile/internal/ssa/_gen/ARM64.rules
index f54a692725..04f43f3137 100644
--- a/src/cmd/compile/internal/ssa/_gen/ARM64.rules
+++ b/src/cmd/compile/internal/ssa/_gen/ARM64.rules
@@ -1814,3 +1814,7 @@
 
 (Select0 (Mul64uover x y)) => (MUL x y)
 (Select1 (Mul64uover x y)) => (NotEqual (CMPconst (UMULH <typ.UInt64> x y) [0]))
+
+// 32 mul 32 -> 64
+(MUL r:(MOVWUreg x) s:(MOVWUreg y)) && r.Uses == 1 && s.Uses == 1 => (UMULL x y)
+(MUL r:(MOVWreg  x) s:(MOVWreg  y)) && r.Uses == 1 && s.Uses == 1 =>  (MULL x y)
diff --git a/src/cmd/compile/internal/ssa/rewriteARM64.go b/src/cmd/compile/internal/ssa/rewriteARM64.go
index 6af1558833..6137ec13a0 100644
--- a/src/cmd/compile/internal/ssa/rewriteARM64.go
+++ b/src/cmd/compile/internal/ssa/rewriteARM64.go
@@ -12556,6 +12556,54 @@ func rewriteValueARM64_OpARM64MUL(v *Value) bool {
 		}
 		break
 	}
+	// match: (MUL r:(MOVWUreg x) s:(MOVWUreg y))
+	// cond: r.Uses == 1 && s.Uses == 1
+	// result: (UMULL x y)
+	for {
+		for _i0 := 0; _i0 <= 1; _i0, v_0, v_1 = _i0+1, v_1, v_0 {
+			r := v_0
+			if r.Op != OpARM64MOVWUreg {
+				continue
+			}
+			x := r.Args[0]
+			s := v_1
+			if s.Op != OpARM64MOVWUreg {
+				continue
+			}
+			y := s.Args[0]
+			if !(r.Uses == 1 && s.Uses == 1) {
+				continue
+			}
+			v.reset(OpARM64UMULL)
+			v.AddArg2(x, y)
+			return true
+		}
+		break
+	}
+	// match: (MUL r:(MOVWreg x) s:(MOVWreg y))
+	// cond: r.Uses == 1 && s.Uses == 1
+	// result: (MULL x y)
+	for {
+		for _i0 := 0; _i0 <= 1; _i0, v_0, v_1 = _i0+1, v_1, v_0 {
+			r := v_0
+			if r.Op != OpARM64MOVWreg {
+				continue
+			}
+			x := r.Args[0]
+			s := v_1
+			if s.Op != OpARM64MOVWreg {
+				continue
+			}
+			y := s.Args[0]
+			if !(r.Uses == 1 && s.Uses == 1) {
+				continue
+			}
+			v.reset(OpARM64MULL)
+			v.AddArg2(x, y)
+			return true
+		}
+		break
+	}
 	return false
 }
 func rewriteValueARM64_OpARM64MULW(v *Value) bool {
diff --git a/test/codegen/arithmetic.go b/test/codegen/arithmetic.go
index 6b2c5529e1..9443d812dc 100644
--- a/test/codegen/arithmetic.go
+++ b/test/codegen/arithmetic.go
@@ -333,6 +333,15 @@ func Fold2NegMul(a, b int) int {
 	return -a * -b
 }
 
+func Mul32(a, b int32) int64 {
+	// arm64:"SMULL" -"MOVW"
+	return int64(a) * int64(b)
+}
+func Mul32U(a, b uint32) uint64 {
+	// arm64:"UMULL" -"MOVWU"
+	return uint64(a) * uint64(b)
+}
+
 // -------------- //
 //    Division    //
 // -------------- //
-- 
2.52.0