cmd/compile: optimise branchs on riscv64

Make use of multi-control values and branch pseudo-instructions to optimise
compiler generated branches.

Change-Id: I7a8bf754db3c2082a390bf6a662ccf18cbcbee39
Reviewed-on: https://go-review.googlesource.com/c/go/+/226400
Reviewed-by: Keith Randall <khr@golang.org>
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

2 files changed, 146 insertions, 11 deletions

diff --git a/src/cmd/compile/internal/ssa/gen/RISCV64.rules b/src/cmd/compile/internal/ssa/gen/RISCV64.rules
index fbd87360ac..9437c8e9d4 100644
--- a/src/cmd/compile/internal/ssa/gen/RISCV64.rules
+++ b/src/cmd/compile/internal/ssa/gen/RISCV64.rules
@@ -445,16 +445,6 @@
 (Addr {sym} base) => (MOVaddr {sym} [0] base)
 (LocalAddr {sym} base _) => (MOVaddr {sym} base)
 
-// Conditional branches
-//
-// cond is 1 if true.
-//
-// TODO(prattmic): RISCV branch instructions take two operands to compare,
-// so we could generate more efficient code by computing the condition in the
-// branch itself. This should be revisited now that the compiler has support
-// for two control values (https://golang.org/cl/196557).
-(If cond yes no) => (BNEZ cond yes no)
-
 // Calls
 (StaticCall  ...) => (CALLstatic  ...)
 (ClosureCall ...) => (CALLclosure ...)
@@ -480,11 +470,31 @@
 (AtomicExchange32 ...) => (LoweredAtomicExchange32 ...)
 (AtomicExchange64 ...) => (LoweredAtomicExchange64 ...)
 
+// Conditional branches
+(If cond yes no) => (BNEZ cond yes no)
+
 // Optimizations
 
-// Absorb SNEZ into branch.
+// Absorb SEQZ/SNEZ into branch.
+(BEQZ (SEQZ x) yes no) => (BNEZ x yes no)
+(BEQZ (SNEZ x) yes no) => (BEQZ x yes no)
+(BNEZ (SEQZ x) yes no) => (BEQZ x yes no)
 (BNEZ (SNEZ x) yes no) => (BNEZ x yes no)
 
+// Convert BEQZ/BNEZ into more optimal branch conditions.
+(BEQZ (SUB x y) yes no) => (BEQ x y yes no)
+(BNEZ (SUB x y) yes no) => (BNE x y yes no)
+(BEQZ (SLT x y) yes no) => (BGE x y yes no)
+(BNEZ (SLT x y) yes no) => (BLT x y yes no)
+(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.
+(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)
+
 // Store zero
 (MOVBstore [off] {sym} ptr (MOVBconst [0]) mem) => (MOVBstorezero [off] {sym} ptr mem)
 (MOVHstore [off] {sym} ptr (MOVHconst [0]) mem) => (MOVHstorezero [off] {sym} ptr mem)
diff --git a/src/cmd/compile/internal/ssa/rewriteRISCV64.go b/src/cmd/compile/internal/ssa/rewriteRISCV64.go
index 6b91c08628..c178290343 100644
--- a/src/cmd/compile/internal/ssa/rewriteRISCV64.go
+++ b/src/cmd/compile/internal/ssa/rewriteRISCV64.go
@@ -5120,7 +5120,105 @@ func rewriteValueRISCV64_OpZeroExt8to64(v *Value) bool {
 }
 func rewriteBlockRISCV64(b *Block) bool {
 	switch b.Kind {
+	case BlockRISCV64BEQ:
+		// match: (BEQ (MOVDconst [0]) cond yes no)
+		// result: (BEQZ 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(BlockRISCV64BEQZ, cond)
+			return true
+		}
+		// match: (BEQ cond (MOVDconst [0]) yes no)
+		// result: (BEQZ 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(BlockRISCV64BEQZ, cond)
+			return true
+		}
+	case BlockRISCV64BEQZ:
+		// match: (BEQZ (SEQZ x) yes no)
+		// result: (BNEZ x yes no)
+		for b.Controls[0].Op == OpRISCV64SEQZ {
+			v_0 := b.Controls[0]
+			x := v_0.Args[0]
+			b.resetWithControl(BlockRISCV64BNEZ, x)
+			return true
+		}
+		// match: (BEQZ (SNEZ x) yes no)
+		// result: (BEQZ x yes no)
+		for b.Controls[0].Op == OpRISCV64SNEZ {
+			v_0 := b.Controls[0]
+			x := v_0.Args[0]
+			b.resetWithControl(BlockRISCV64BEQZ, x)
+			return true
+		}
+		// match: (BEQZ (SUB x y) yes no)
+		// result: (BEQ x y yes no)
+		for b.Controls[0].Op == OpRISCV64SUB {
+			v_0 := b.Controls[0]
+			y := v_0.Args[1]
+			x := v_0.Args[0]
+			b.resetWithControl2(BlockRISCV64BEQ, x, y)
+			return true
+		}
+		// match: (BEQZ (SLT x y) yes no)
+		// result: (BGE x y yes no)
+		for b.Controls[0].Op == OpRISCV64SLT {
+			v_0 := b.Controls[0]
+			y := v_0.Args[1]
+			x := v_0.Args[0]
+			b.resetWithControl2(BlockRISCV64BGE, x, y)
+			return true
+		}
+		// match: (BEQZ (SLTU x y) yes no)
+		// result: (BGEU x y yes no)
+		for b.Controls[0].Op == OpRISCV64SLTU {
+			v_0 := b.Controls[0]
+			y := v_0.Args[1]
+			x := v_0.Args[0]
+			b.resetWithControl2(BlockRISCV64BGEU, x, y)
+			return true
+		}
+	case BlockRISCV64BNE:
+		// match: (BNE (MOVDconst [0]) cond yes no)
+		// result: (BNEZ 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(BlockRISCV64BNEZ, cond)
+			return true
+		}
+		// match: (BNE cond (MOVDconst [0]) yes no)
+		// result: (BNEZ 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(BlockRISCV64BNEZ, cond)
+			return true
+		}
 	case BlockRISCV64BNEZ:
+		// match: (BNEZ (SEQZ x) yes no)
+		// result: (BEQZ x yes no)
+		for b.Controls[0].Op == OpRISCV64SEQZ {
+			v_0 := b.Controls[0]
+			x := v_0.Args[0]
+			b.resetWithControl(BlockRISCV64BEQZ, x)
+			return true
+		}
 		// match: (BNEZ (SNEZ x) yes no)
 		// result: (BNEZ x yes no)
 		for b.Controls[0].Op == OpRISCV64SNEZ {
@@ -5129,6 +5227,33 @@ func rewriteBlockRISCV64(b *Block) bool {
 			b.resetWithControl(BlockRISCV64BNEZ, x)
 			return true
 		}
+		// match: (BNEZ (SUB x y) yes no)
+		// result: (BNE x y yes no)
+		for b.Controls[0].Op == OpRISCV64SUB {
+			v_0 := b.Controls[0]
+			y := v_0.Args[1]
+			x := v_0.Args[0]
+			b.resetWithControl2(BlockRISCV64BNE, x, y)
+			return true
+		}
+		// match: (BNEZ (SLT x y) yes no)
+		// result: (BLT x y yes no)
+		for b.Controls[0].Op == OpRISCV64SLT {
+			v_0 := b.Controls[0]
+			y := v_0.Args[1]
+			x := v_0.Args[0]
+			b.resetWithControl2(BlockRISCV64BLT, x, y)
+			return true
+		}
+		// match: (BNEZ (SLTU x y) yes no)
+		// result: (BLTU x y yes no)
+		for b.Controls[0].Op == OpRISCV64SLTU {
+			v_0 := b.Controls[0]
+			y := v_0.Args[1]
+			x := v_0.Args[0]
+			b.resetWithControl2(BlockRISCV64BLTU, x, y)
+			return true
+		}
 	case BlockIf:
 		// match: (If cond yes no)
 		// result: (BNEZ cond yes no)