From: Meng Zhuo <mengzhuo@iscas.ac.cn>
Date: Thu, 11 Sep 2025 09:21:02 +0000 (+0800)
Subject: cmd/compile: combine doubling with shift on riscv64
X-Git-Tag: go1.26rc1~865
X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=2469e92d8c;p=gostls13.git

cmd/compile: combine doubling with shift on riscv64

Change-Id: I4bee2770fedf97e35b5a5b9187a8ba3c41f9ec2e
Reviewed-on: https://go-review.googlesource.com/c/go/+/702697
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Joel Sing <joel@sing.id.au>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Keith Randall <khr@google.com>
---

diff --git a/src/cmd/compile/internal/ssa/_gen/RISCV64.rules b/src/cmd/compile/internal/ssa/_gen/RISCV64.rules
index e14de328ea..7059273eb2 100644
--- a/src/cmd/compile/internal/ssa/_gen/RISCV64.rules
+++ b/src/cmd/compile/internal/ssa/_gen/RISCV64.rules
@@ -782,6 +782,10 @@
 (SRLI [x] (MOVDconst [y])) => (MOVDconst [int64(uint64(y) >> uint32(x))])
 (SRAI [x] (MOVDconst [y])) => (MOVDconst [int64(y) >> uint32(x)])
 
+// Combine doubling via addition with shift.
+(SLLI <t> [c] (ADD x x)) && c < t.Size() * 8 - 1 => (SLLI <t> [c+1] x)
+(SLLI <t> [c] (ADD x x)) && c >= t.Size() * 8 - 1 => (MOVDconst [0])
+
 // SLTI/SLTIU with constants.
 (SLTI  [x] (MOVDconst [y])) => (MOVDconst [b2i(int64(y) < int64(x))])
 (SLTIU [x] (MOVDconst [y])) => (MOVDconst [b2i(uint64(y) < uint64(x))])
diff --git a/src/cmd/compile/internal/ssa/rewriteRISCV64.go b/src/cmd/compile/internal/ssa/rewriteRISCV64.go
index 5723327bc9..a7b4cf1bc4 100644
--- a/src/cmd/compile/internal/ssa/rewriteRISCV64.go
+++ b/src/cmd/compile/internal/ssa/rewriteRISCV64.go
@@ -7185,6 +7185,42 @@ func rewriteValueRISCV64_OpRISCV64SLLI(v *Value) bool {
 		v.AuxInt = int64ToAuxInt(y << uint32(x))
 		return true
 	}
+	// match: (SLLI <t> [c] (ADD x x))
+	// cond: c < t.Size() * 8 - 1
+	// result: (SLLI <t> [c+1] x)
+	for {
+		t := v.Type
+		c := auxIntToInt64(v.AuxInt)
+		if v_0.Op != OpRISCV64ADD {
+			break
+		}
+		x := v_0.Args[1]
+		if x != v_0.Args[0] || !(c < t.Size()*8-1) {
+			break
+		}
+		v.reset(OpRISCV64SLLI)
+		v.Type = t
+		v.AuxInt = int64ToAuxInt(c + 1)
+		v.AddArg(x)
+		return true
+	}
+	// match: (SLLI <t> [c] (ADD x x))
+	// cond: c >= t.Size() * 8 - 1
+	// result: (MOVDconst [0])
+	for {
+		t := v.Type
+		c := auxIntToInt64(v.AuxInt)
+		if v_0.Op != OpRISCV64ADD {
+			break
+		}
+		x := v_0.Args[1]
+		if x != v_0.Args[0] || !(c >= t.Size()*8-1) {
+			break
+		}
+		v.reset(OpRISCV64MOVDconst)
+		v.AuxInt = int64ToAuxInt(0)
+		return true
+	}
 	return false
 }
 func rewriteValueRISCV64_OpRISCV64SLLW(v *Value) bool {
diff --git a/test/codegen/shift.go b/test/codegen/shift.go
index 1c71b0f3ef..7385058726 100644
--- a/test/codegen/shift.go
+++ b/test/codegen/shift.go
@@ -122,27 +122,41 @@ func rshConst64x32(v int64) int64 {
 func lshConst32x1Add(x int32) int32 {
 	// amd64:"SHLL\t[$]2"
 	// loong64:"SLL\t[$]2"
+	// riscv64:"SLLI\t[$]2"
 	return (x + x) << 1
 }
 
 func lshConst64x1Add(x int64) int64 {
 	// amd64:"SHLQ\t[$]2"
 	// loong64:"SLLV\t[$]2"
+	// riscv64:"SLLI\t[$]2"
 	return (x + x) << 1
 }
 
 func lshConst32x2Add(x int32) int32 {
 	// amd64:"SHLL\t[$]3"
 	// loong64:"SLL\t[$]3"
+	// riscv64:"SLLI\t[$]3"
 	return (x + x) << 2
 }
 
 func lshConst64x2Add(x int64) int64 {
 	// amd64:"SHLQ\t[$]3"
 	// loong64:"SLLV\t[$]3"
+	// riscv64:"SLLI\t[$]3"
 	return (x + x) << 2
 }
 
+func lshConst32x31Add(x int32) int32 {
+	// riscv64:-"SLLI","MOV\t[$]0"
+	return (x + x) << 31
+}
+
+func lshConst64x63Add(x int64) int64 {
+	// riscv64:-"SLLI","MOV\t[$]0"
+	return (x + x) << 63
+}
+
 // ------------------ //
 //   masked shifts    //
 // ------------------ //