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cmd/compile: simplify Slicemask on riscv64

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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>
This commit is contained in:
Joel Sing 2020-02-26 04:01:29 +11:00
parent c27dd0c9e5
commit 025a4faf5f
2 changed files with 10 additions and 18 deletions
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3
src/cmd/compile/internal/ssa/gen/RISCV64.rules
View File

@ -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.

25
src/cmd/compile/internal/ssa/rewriteRISCV64.go
View File

@ -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
}
}