From 83d94daec2636badf02ecda18f7a7c1f4eb1fd74 Mon Sep 17 00:00:00 2001
From: Joel Sing <joel@sing.id.au>
Date: Tue, 30 Aug 2022 18:59:53 +1000
Subject: [PATCH] cmd/compile: avoid the use of XOR for boolean equality on
 riscv64

The use of SEQZ/SNEZ and SUB allows for other optimisations to be utilised,
particularly absorption into branch equality conditions.

Change-Id: I74e7d6a07a8decc1bdb651660c322bcc6eb6a10a
Reviewed-on: https://go-review.googlesource.com/c/go/+/428216
Run-TryBot: Joel Sing <joel@sing.id.au>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Meng Zhuo <mzh@golangcn.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
---
 .../compile/internal/ssa/gen/RISCV64.rules    |  4 ++--
 .../compile/internal/ssa/rewriteRISCV64.go    | 24 +++++++++++++++----
 2 files changed, 22 insertions(+), 6 deletions(-)

diff --git a/src/cmd/compile/internal/ssa/gen/RISCV64.rules b/src/cmd/compile/internal/ssa/gen/RISCV64.rules
index c2f1c16b6b..5c3c862571 100644
--- a/src/cmd/compile/internal/ssa/gen/RISCV64.rules
+++ b/src/cmd/compile/internal/ssa/gen/RISCV64.rules
@@ -534,8 +534,8 @@
 // Boolean ops; 0=false, 1=true
 (AndB ...) => (AND ...)
 (OrB  ...) => (OR  ...)
-(EqB  x y) => (SEQZ (XOR <typ.Bool> x y))
-(NeqB ...) => (XOR ...)
+(EqB  x y) => (SEQZ (SUB <typ.Bool> x y))
+(NeqB x y) => (SNEZ (SUB <typ.Bool> x y))
 (Not  ...) => (SEQZ ...)
 
 // Lowering pointer arithmetic
diff --git a/src/cmd/compile/internal/ssa/rewriteRISCV64.go b/src/cmd/compile/internal/ssa/rewriteRISCV64.go
index 097232ab18..05c646e4a6 100644
--- a/src/cmd/compile/internal/ssa/rewriteRISCV64.go
+++ b/src/cmd/compile/internal/ssa/rewriteRISCV64.go
@@ -406,8 +406,7 @@ func rewriteValueRISCV64(v *Value) bool {
 	case OpNeq8:
 		return rewriteValueRISCV64_OpNeq8(v)
 	case OpNeqB:
-		v.Op = OpRISCV64XOR
-		return true
+		return rewriteValueRISCV64_OpNeqB(v)
 	case OpNeqPtr:
 		return rewriteValueRISCV64_OpNeqPtr(v)
 	case OpNilCheck:
@@ -1121,12 +1120,12 @@ func rewriteValueRISCV64_OpEqB(v *Value) bool {
 	b := v.Block
 	typ := &b.Func.Config.Types
 	// match: (EqB x y)
-	// result: (SEQZ (XOR <typ.Bool> x y))
+	// result: (SEQZ (SUB <typ.Bool> x y))
 	for {
 		x := v_0
 		y := v_1
 		v.reset(OpRISCV64SEQZ)
-		v0 := b.NewValue0(v.Pos, OpRISCV64XOR, typ.Bool)
+		v0 := b.NewValue0(v.Pos, OpRISCV64SUB, typ.Bool)
 		v0.AddArg2(x, y)
 		v.AddArg(v0)
 		return true
@@ -2970,6 +2969,23 @@ func rewriteValueRISCV64_OpNeq8(v *Value) bool {
 		return true
 	}
 }
+func rewriteValueRISCV64_OpNeqB(v *Value) bool {
+	v_1 := v.Args[1]
+	v_0 := v.Args[0]
+	b := v.Block
+	typ := &b.Func.Config.Types
+	// match: (NeqB x y)
+	// result: (SNEZ (SUB <typ.Bool> x y))
+	for {
+		x := v_0
+		y := v_1
+		v.reset(OpRISCV64SNEZ)
+		v0 := b.NewValue0(v.Pos, OpRISCV64SUB, typ.Bool)
+		v0.AddArg2(x, y)
+		v.AddArg(v0)
+		return true
+	}
+}
 func rewriteValueRISCV64_OpNeqPtr(v *Value) bool {
 	v_1 := v.Args[1]
 	v_0 := v.Args[0]
-- 
2.48.1