cmd/compile: simplify Slicemask on riscv64

Slicemask can be performed with three immediate instructions, rather than the
six currently in use.

Change-Id: I3f8ca2d5affd1403db8fa79b356f248e6e9332c5
Reviewed-on: https://go-review.googlesource.com/c/go/+/220923
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 1ffb9575e0c244986cf213a984e6a76dfdde6432..316e5f37262da5907a5579efa17876a2de710443 100644 (file)
--- a/src/cmd/compile/internal/ssa/gen/RISCV64.rules
+++ b/src/cmd/compile/internal/ssa/gen/RISCV64.rules
@@ -141,8 +141,7 @@
 // For positive x, bit 63 of x-1 is always 0, so the result is -1.
 // For zero x, bit 63 of x-1 is 1, so the result is 0.
 //
-// TODO(prattmic): Use XORconst etc instead of XOR (MOVDconst).
-(Slicemask <t> x) -> (XOR (MOVDconst [-1]) (SRA <t> (SUB <t> x (MOVDconst [1])) (MOVDconst [63])))
+(Slicemask <t> x) -> (XORI [-1] (SRAI <t> [63] (ADDI <t> [-1] x)))
 
 // Truncations
 // We ignore the unused high parts of registers, so truncates are just copies.

diff --git a/src/cmd/compile/internal/ssa/rewriteRISCV64.go b/src/cmd/compile/internal/ssa/rewriteRISCV64.go
index 61da7a41bdb55108a076ae3177272bcf10cc2031..3b8d42b035f15fad846d59bb9abf6c770e8c5078 100644 (file)
--- a/src/cmd/compile/internal/ssa/rewriteRISCV64.go
+++ b/src/cmd/compile/internal/ssa/rewriteRISCV64.go
@@ -4230,27 +4230,20 @@ func rewriteValueRISCV64_OpSignExt8to64(v *Value) bool {
 func rewriteValueRISCV64_OpSlicemask(v *Value) bool {
        v_0 := v.Args[0]
        b := v.Block
-       typ := &b.Func.Config.Types
        // match: (Slicemask <t> x)
-       // result: (XOR (MOVDconst [-1]) (SRA <t> (SUB <t> x (MOVDconst [1])) (MOVDconst [63])))
+       // result: (XORI [-1] (SRAI <t> [63] (ADDI <t> [-1] x)))
        for {
                t := v.Type
                x := v_0
-               v.reset(OpRISCV64XOR)
-               v0 := b.NewValue0(v.Pos, OpRISCV64MOVDconst, typ.UInt64)
-               v0.AuxInt = -1
+               v.reset(OpRISCV64XORI)
+               v.AuxInt = -1
+               v0 := b.NewValue0(v.Pos, OpRISCV64SRAI, t)
+               v0.AuxInt = 63
+               v1 := b.NewValue0(v.Pos, OpRISCV64ADDI, t)
+               v1.AuxInt = -1
+               v1.AddArg(x)
+               v0.AddArg(v1)
                v.AddArg(v0)
-               v1 := b.NewValue0(v.Pos, OpRISCV64SRA, t)
-               v2 := b.NewValue0(v.Pos, OpRISCV64SUB, t)
-               v2.AddArg(x)
-               v3 := b.NewValue0(v.Pos, OpRISCV64MOVDconst, typ.UInt64)
-               v3.AuxInt = 1
-               v2.AddArg(v3)
-               v1.AddArg(v2)
-               v4 := b.NewValue0(v.Pos, OpRISCV64MOVDconst, typ.UInt64)
-               v4.AuxInt = 63
-               v1.AddArg(v4)
-               v.AddArg(v1)
                return true
        }
 }