cmd/compile: convert branch with zero to more optimal branch zero on riscv64

Convert BLT and BGE with a zero valued constant to BGTZ/BLTZ/BLEZ/BGEZ as
appropriate.

Removes over 4,500 instructions from the go binary on riscv64.

Change-Id: Icc266e968b126ba04863ec88529630a9dd44498b
Reviewed-on: https://go-review.googlesource.com/c/go/+/342849
Trust: Joel Sing <joel@sing.id.au>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Run-TryBot: Cherry Mui <cherryyz@google.com>
TryBot-Result: Go Bot <gobot@golang.org>

2 files changed, 51 insertions, 1 deletions

diff --git a/src/cmd/compile/internal/ssa/gen/RISCV64.rules b/src/cmd/compile/internal/ssa/gen/RISCV64.rules
index 1acef2a273..1414b2b34d 100644
--- a/src/cmd/compile/internal/ssa/gen/RISCV64.rules
+++ b/src/cmd/compile/internal/ssa/gen/RISCV64.rules
@@ -596,11 +596,15 @@
 (BEQZ (SLTU x y) yes no) => (BGEU x y yes no)
 (BNEZ (SLTU x y) yes no) => (BLTU x y yes no)
 
-// Convert branch with zero to BEQZ/BNEZ.
+// Convert branch with zero to more optimal branch zero.
 (BEQ (MOVDconst [0]) cond yes no) => (BEQZ cond yes no)
 (BEQ cond (MOVDconst [0]) yes no) => (BEQZ cond yes no)
 (BNE (MOVDconst [0]) cond yes no) => (BNEZ cond yes no)
 (BNE cond (MOVDconst [0]) yes no) => (BNEZ cond yes no)
+(BLT (MOVDconst [0]) cond yes no) => (BGTZ cond yes no)
+(BLT cond (MOVDconst [0]) yes no) => (BLTZ cond yes no)
+(BGE (MOVDconst [0]) cond yes no) => (BLEZ cond yes no)
+(BGE cond (MOVDconst [0]) yes no) => (BGEZ cond yes no)
 
 // Store zero
 (MOVBstore [off] {sym} ptr (MOVDconst [0]) mem) => (MOVBstorezero [off] {sym} ptr mem)
diff --git a/src/cmd/compile/internal/ssa/rewriteRISCV64.go b/src/cmd/compile/internal/ssa/rewriteRISCV64.go
index e9f17206de..9323cda55d 100644
--- a/src/cmd/compile/internal/ssa/rewriteRISCV64.go
+++ b/src/cmd/compile/internal/ssa/rewriteRISCV64.go
@@ -6129,6 +6129,52 @@ func rewriteBlockRISCV64(b *Block) bool {
 			b.resetWithControl2(BlockRISCV64BGEU, x, y)
 			return true
 		}
+	case BlockRISCV64BGE:
+		// match: (BGE (MOVDconst [0]) cond yes no)
+		// result: (BLEZ cond yes no)
+		for b.Controls[0].Op == OpRISCV64MOVDconst {
+			v_0 := b.Controls[0]
+			if auxIntToInt64(v_0.AuxInt) != 0 {
+				break
+			}
+			cond := b.Controls[1]
+			b.resetWithControl(BlockRISCV64BLEZ, cond)
+			return true
+		}
+		// match: (BGE cond (MOVDconst [0]) yes no)
+		// result: (BGEZ cond yes no)
+		for b.Controls[1].Op == OpRISCV64MOVDconst {
+			cond := b.Controls[0]
+			v_1 := b.Controls[1]
+			if auxIntToInt64(v_1.AuxInt) != 0 {
+				break
+			}
+			b.resetWithControl(BlockRISCV64BGEZ, cond)
+			return true
+		}
+	case BlockRISCV64BLT:
+		// match: (BLT (MOVDconst [0]) cond yes no)
+		// result: (BGTZ cond yes no)
+		for b.Controls[0].Op == OpRISCV64MOVDconst {
+			v_0 := b.Controls[0]
+			if auxIntToInt64(v_0.AuxInt) != 0 {
+				break
+			}
+			cond := b.Controls[1]
+			b.resetWithControl(BlockRISCV64BGTZ, cond)
+			return true
+		}
+		// match: (BLT cond (MOVDconst [0]) yes no)
+		// result: (BLTZ cond yes no)
+		for b.Controls[1].Op == OpRISCV64MOVDconst {
+			cond := b.Controls[0]
+			v_1 := b.Controls[1]
+			if auxIntToInt64(v_1.AuxInt) != 0 {
+				break
+			}
+			b.resetWithControl(BlockRISCV64BLTZ, cond)
+			return true
+		}
 	case BlockRISCV64BNE:
 		// match: (BNE (MOVDconst [0]) cond yes no)
 		// result: (BNEZ cond yes no)