cmd/compile: optimize subtraction of zero on riscv64

Change-Id: I9a994b01e9fecb13077c30df4b7677d40d179cce
Reviewed-on: https://go-review.googlesource.com/c/go/+/221681
Reviewed-by: Cherry Zhang <cherryyz@google.com>

diff --git a/src/cmd/compile/internal/ssa/gen/RISCV64.rules b/src/cmd/compile/internal/ssa/gen/RISCV64.rules
index 3fd482b50c5da0d58fdf0ff86660789d8712239b..9c1169dc67fa44d10c58e3dfc24a735991e07099 100644 (file)
--- a/src/cmd/compile/internal/ssa/gen/RISCV64.rules
+++ b/src/cmd/compile/internal/ssa/gen/RISCV64.rules
@@ -467,5 +467,14 @@
 (SUB x (MOVWconst [val])) && is32Bit(-val) -> (ADDI [-val] x)
 (SUB x (MOVDconst [val])) && is32Bit(-val) -> (ADDI [-val] x)
 
+// Subtraction of zero.
+(SUB x (MOVBconst [0])) -> x
+(SUB x (MOVHconst [0])) -> x
+(SUB x (MOVWconst [0])) -> x
+(SUB x (MOVDconst [0])) -> x
+
+// Subtraction of zero with sign extension.
+(SUBW x (MOVWconst [0])) -> (ADDIW [0] x)
+
 // remove redundant *const ops
 (ADDI [0]  x) -> x

diff --git a/src/cmd/compile/internal/ssa/rewriteRISCV64.go b/src/cmd/compile/internal/ssa/rewriteRISCV64.go
index 128f7bb2b292a721c6dcab8e239e222a9fcdf45f..b363b10ad780bef2aab6d0df0b7cc93134cad23c 100644 (file)
--- a/src/cmd/compile/internal/ssa/rewriteRISCV64.go
+++ b/src/cmd/compile/internal/ssa/rewriteRISCV64.go
@@ -406,6 +406,8 @@ func rewriteValueRISCV64(v *Value) bool {
                return rewriteValueRISCV64_OpRISCV64MOVWstore(v)
        case OpRISCV64SUB:
                return rewriteValueRISCV64_OpRISCV64SUB(v)
+       case OpRISCV64SUBW:
+               return rewriteValueRISCV64_OpRISCV64SUBW(v)
        case OpRotateLeft16:
                return rewriteValueRISCV64_OpRotateLeft16(v)
        case OpRotateLeft32:
@@ -2950,6 +2952,63 @@ func rewriteValueRISCV64_OpRISCV64SUB(v *Value) bool {
                v.AddArg(x)
                return true
        }
+       // match: (SUB x (MOVBconst [0]))
+       // result: x
+       for {
+               x := v_0
+               if v_1.Op != OpRISCV64MOVBconst || v_1.AuxInt != 0 {
+                       break
+               }
+               v.copyOf(x)
+               return true
+       }
+       // match: (SUB x (MOVHconst [0]))
+       // result: x
+       for {
+               x := v_0
+               if v_1.Op != OpRISCV64MOVHconst || v_1.AuxInt != 0 {
+                       break
+               }
+               v.copyOf(x)
+               return true
+       }
+       // match: (SUB x (MOVWconst [0]))
+       // result: x
+       for {
+               x := v_0
+               if v_1.Op != OpRISCV64MOVWconst || v_1.AuxInt != 0 {
+                       break
+               }
+               v.copyOf(x)
+               return true
+       }
+       // match: (SUB x (MOVDconst [0]))
+       // result: x
+       for {
+               x := v_0
+               if v_1.Op != OpRISCV64MOVDconst || v_1.AuxInt != 0 {
+                       break
+               }
+               v.copyOf(x)
+               return true
+       }
+       return false
+}
+func rewriteValueRISCV64_OpRISCV64SUBW(v *Value) bool {
+       v_1 := v.Args[1]
+       v_0 := v.Args[0]
+       // match: (SUBW x (MOVWconst [0]))
+       // result: (ADDIW [0] x)
+       for {
+               x := v_0
+               if v_1.Op != OpRISCV64MOVWconst || v_1.AuxInt != 0 {
+                       break
+               }
+               v.reset(OpRISCV64ADDIW)
+               v.AuxInt = 0
+               v.AddArg(x)
+               return true
+       }
        return false
 }
 func rewriteValueRISCV64_OpRotateLeft16(v *Value) bool {