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cmd/compile: constant fold SHLxconst of a constant on amd64 

These rules fire in particular when comparing to a constant
string of length two. They should trigger even more after CL 220499.

file    before    after     Δ       %       
compile 20639976  20635880  -4096   -0.020% 
total   116003456 115999360 -4096   -0.004% 

Change-Id: I21c1c02cf32d710d7a4eb12efab00f02796ccb84
Reviewed-on: https://go-review.googlesource.com/c/go/+/220694
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
This commit is contained in:
Josh Bleecher Snyder 2020-02-22 21:47:49 -08:00
parent 9c60094986
commit f510cddcd1
2 changed files with 27 additions and 0 deletions
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3
src/cmd/compile/internal/ssa/gen/AMD64.rules
View File

@ -1482,6 +1482,9 @@
(XORQ x x) -> (MOVQconst [0])
(XORL x x) -> (MOVLconst [0])
(SHLLconst [d] (MOVLconst [c])) -> (MOVLconst [int64(int32(c)) << uint64(d)])
(SHLQconst [d] (MOVQconst [c])) -> (MOVQconst [c << uint64(d)])
// Fold NEG into ADDconst/MULconst. Take care to keep c in 32 bit range.
(NEGQ (ADDQconst [c] (NEGQ x))) && c != -(1<<31) -> (ADDQconst [-c] x)
(MULQconst [c] (NEGQ x)) && c != -(1<<31) -> (MULQconst [-c] x)

24
src/cmd/compile/internal/ssa/rewriteAMD64.go
View File

@ -31354,6 +31354,18 @@ func rewriteValueAMD64_OpAMD64SHLLconst(v *Value) bool {
v.AddArg(x)
return true
}
// match: (SHLLconst [d] (MOVLconst [c]))
// result: (MOVLconst [int64(int32(c)) << uint64(d)])
for {
d := v.AuxInt
if v_0.Op != OpAMD64MOVLconst {
break
}
c := v_0.AuxInt
v.reset(OpAMD64MOVLconst)
v.AuxInt = int64(int32(c)) << uint64(d)
return true
}
return false
}
func rewriteValueAMD64_OpAMD64SHLQ(v *Value) bool {
@ -31586,6 +31598,18 @@ func rewriteValueAMD64_OpAMD64SHLQconst(v *Value) bool {
v.AddArg(x)
return true
}
// match: (SHLQconst [d] (MOVQconst [c]))
// result: (MOVQconst [c << uint64(d)])
for {
d := v.AuxInt
if v_0.Op != OpAMD64MOVQconst {
break
}
c := v_0.AuxInt
v.reset(OpAMD64MOVQconst)
v.AuxInt = c << uint64(d)
return true
}
return false
}
func rewriteValueAMD64_OpAMD64SHRB(v *Value) bool {