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cmd/compile: deadcode for LoweredMuluhilo on riscv64

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This is a follow up of CL 425101 on RISCV64.

According to RISCV Volume 1, Unprivileged Spec v. 20191213 Chapter 7.1:
If both the high and low bits of the same product are required, then the
recommended code sequence is: MULH[[S]U] rdh, rs1, rs2; MUL rdl, rs1, rs2
(source register specifiers must be in same order and rdh cannot be the
same as rs1 or rs2). Microarchitectures can then fuse these into a single
multiply operation instead of performing two separate multiplies.

So we should not split Muluhilo to separate instructions.

Updates #54607

Change-Id: If47461f3aaaf00e27cd583a9990e144fb8bcdb17
Reviewed-on: https://go-review.googlesource.com/c/go/+/425203
Auto-Submit: Keith Randall <khr@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Wayne Zuo <wdvxdr@golangcn.org>
Reviewed-by: Keith Randall <khr@google.com>
Reviewed-by: Keith Randall <khr@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>
This commit is contained in:
Wayne Zuo 2022-08-24 22:17:51 +08:00 • committed by Gopher Robot
parent cfae70ccb1
commit b60432df14
3 changed files with 52 additions and 0 deletions
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46
src/cmd/compile/internal/ssa/rewriteRISCV64.go
View file

@ -605,6 +605,10 @@ func rewriteValueRISCV64(v *Value) bool {
return rewriteValueRISCV64_OpRsh8x64(v)
case OpRsh8x8:
return rewriteValueRISCV64_OpRsh8x8(v)
case OpSelect0:
return rewriteValueRISCV64_OpSelect0(v)
case OpSelect1:
return rewriteValueRISCV64_OpSelect1(v)
case OpSignExt16to32:
v.Op = OpRISCV64MOVHreg
return true
@ -6030,6 +6034,48 @@ func rewriteValueRISCV64_OpRsh8x8(v *Value) bool {
return true
}
}
func rewriteValueRISCV64_OpSelect0(v *Value) bool {
v_0 := v.Args[0]
// match: (Select0 m:(LoweredMuluhilo x y))
// cond: m.Uses == 1
// result: (MULHU x y)
for {
m := v_0
if m.Op != OpRISCV64LoweredMuluhilo {
break
}
y := m.Args[1]
x := m.Args[0]
if !(m.Uses == 1) {
break
}
v.reset(OpRISCV64MULHU)
v.AddArg2(x, y)
return true
}
return false
}
func rewriteValueRISCV64_OpSelect1(v *Value) bool {
v_0 := v.Args[0]
// match: (Select1 m:(LoweredMuluhilo x y))
// cond: m.Uses == 1
// result: (MUL x y)
for {
m := v_0
if m.Op != OpRISCV64LoweredMuluhilo {
break
}
y := m.Args[1]
x := m.Args[0]
if !(m.Uses == 1) {
break
}
v.reset(OpRISCV64MUL)
v.AddArg2(x, y)
return true
}
return false
}
func rewriteValueRISCV64_OpSlicemask(v *Value) bool {
v_0 := v.Args[0]
b := v.Block