From 3a29ebeef985efb12d2b8670f50b146e9a2815ca Mon Sep 17 00:00:00 2001
From: Joel Sing <joel@sing.id.au>
Date: Sat, 21 Feb 2026 03:29:09 +1100
Subject: [PATCH] cmd/compile: additional optimisation for CZEROEQZ/CZERONEZ on
 riscv64

Negation on a condition can be eliminated.

Change-Id: I94fab5f019cbaebb2ca589e1d8796a9cb72f3894
Reviewed-on: https://go-review.googlesource.com/c/go/+/748401
Reviewed-by: Xueqi Luo <1824368278@qq.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Julian Zhu <jz531210@gmail.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Keith Randall <khr@golang.org>
---
 .../compile/internal/ssa/_gen/RISCV64.rules   |  1 +
 .../compile/internal/ssa/rewriteRISCV64.go    | 24 +++++++++++++++++++
 test/codegen/condmove.go                      |  2 +-
 3 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/src/cmd/compile/internal/ssa/_gen/RISCV64.rules b/src/cmd/compile/internal/ssa/_gen/RISCV64.rules
index 06130d242d..9e3911ea0c 100644
--- a/src/cmd/compile/internal/ssa/_gen/RISCV64.rules
+++ b/src/cmd/compile/internal/ssa/_gen/RISCV64.rules
@@ -866,6 +866,7 @@
 	(OR (CZEROEQZ <t> x (MOVBUreg <typ.UInt64> cond)) (CZERONEZ <t> y (MOVBUreg <typ.UInt64> cond)))
 (CZERO(EQ|NE)Z x (SNEZ y)) => (CZERO(EQ|NE)Z x y)
 (CZERO(EQ|NE)Z x (SEQZ y)) => (CZERO(NE|EQ)Z x y)
+(CZERO(EQ|NE)Z x (NEG y)) => (CZERO(EQ|NE)Z x y)
 (CZEROEQZ x x) => x
 (CZERONEZ x x) => (MOVDconst [0])
 (CZERO(EQ|NE)Z (MOVDconst [0]) _) => (MOVDconst [0])
diff --git a/src/cmd/compile/internal/ssa/rewriteRISCV64.go b/src/cmd/compile/internal/ssa/rewriteRISCV64.go
index 1700604422..d5c52c5eb1 100644
--- a/src/cmd/compile/internal/ssa/rewriteRISCV64.go
+++ b/src/cmd/compile/internal/ssa/rewriteRISCV64.go
@@ -3588,6 +3588,18 @@ func rewriteValueRISCV64_OpRISCV64CZEROEQZ(v *Value) bool {
 		v.AddArg2(x, y)
 		return true
 	}
+	// match: (CZEROEQZ x (NEG y))
+	// result: (CZEROEQZ x y)
+	for {
+		x := v_0
+		if v_1.Op != OpRISCV64NEG {
+			break
+		}
+		y := v_1.Args[0]
+		v.reset(OpRISCV64CZEROEQZ)
+		v.AddArg2(x, y)
+		return true
+	}
 	// match: (CZEROEQZ x x)
 	// result: x
 	for {
@@ -3637,6 +3649,18 @@ func rewriteValueRISCV64_OpRISCV64CZERONEZ(v *Value) bool {
 		v.AddArg2(x, y)
 		return true
 	}
+	// match: (CZERONEZ x (NEG y))
+	// result: (CZERONEZ x y)
+	for {
+		x := v_0
+		if v_1.Op != OpRISCV64NEG {
+			break
+		}
+		y := v_1.Args[0]
+		v.reset(OpRISCV64CZERONEZ)
+		v.AddArg2(x, y)
+		return true
+	}
 	// match: (CZERONEZ x x)
 	// result: (MOVDconst [0])
 	for {
diff --git a/test/codegen/condmove.go b/test/codegen/condmove.go
index bd2d1540b4..93159d1ca4 100644
--- a/test/codegen/condmove.go
+++ b/test/codegen/condmove.go
@@ -534,6 +534,6 @@ func constantTimeSelect(v, x, y int) int {
 	// amd64:"CMOVQ"
 	// arm64:"CSEL"
 	// riscv64/rva20u64,riscv64/rva22u64:"SNEZ" "NEG" "AND" "OR"
-	// riscv64/rva23u64:"NEG" "CZERONEZ" "CZEROEQZ" "OR" -"SNEZ" -"AND"
+	// riscv64/rva23u64:"CZERONEZ" "CZEROEQZ" "OR" -"SNEZ" -"NEG" -"AND"
 	return subtle.ConstantTimeSelect(v, x, y)
 }