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[AArch64][GlobalISel] Don't bail out of the select(cmp(a, b)) -> csel optimization with multiple users. 

It can still be beneficial to do the optimization if the result of the compare
is used by *another* select.

Differential Revision: https://reviews.llvm.org/D73511
This commit is contained in:
Amara Emerson 2020-01-27 15:57:16 -08:00
parent 5547919280
commit 14c2cf8e18
2 changed files with 47 additions and 3 deletions
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13
llvm/lib/Target/AArch64/AArch64InstructionSelector.cpp
View File

@ -3508,8 +3508,17 @@ bool AArch64InstructionSelector::tryOptSelect(MachineInstr &I) const {
MachineInstr *CondDef = MRI.getVRegDef(I.getOperand(1).getReg());
while (CondDef) {
// We can only fold if all of the defs have one use.
if (!MRI.hasOneUse(CondDef->getOperand(0).getReg()))
return false;
Register CondDefReg = CondDef->getOperand(0).getReg();
if (!MRI.hasOneUse(CondDefReg)) {
// Unless it's another select.
for (auto UI = MRI.use_instr_begin(CondDefReg), UE = MRI.use_instr_end();
UI != UE; ++UI) {
if (CondDef == &*UI)
continue;
if (UI->getOpcode() != TargetOpcode::G_SELECT)
return false;
}
}
// We can skip over G_TRUNC since the condition is 1-bit.
// Truncating/extending can have no impact on the value.

37
llvm/test/CodeGen/AArch64/GlobalISel/fold-fp-select.mir
View File

@ -4,7 +4,7 @@
# Verify the following:
#
# - We can fold compares into selects.
# - This only happens when the result of the compare is only used by the select.
# - This only happens when the result of the compare is only used by selects.
#
# Also verify that, for now:
#
@ -47,6 +47,41 @@ body: |
$s0 = COPY %4(s32)
RET_ReallyLR implicit $s0
...
---
name: fcmp_more_than_one_select
alignment: 4
legalized: true
regBankSelected: true
tracksRegLiveness: true
body: |
bb.0:
liveins: $s0, $s1, $w1
; CHECK-LABEL: name: fcmp_more_than_one_select
; CHECK: liveins: $s0, $s1, $w1
; CHECK: [[COPY:%[0-9]+]]:fpr32 = COPY $s0
; CHECK: [[COPY1:%[0-9]+]]:fpr32 = COPY $s1
; CHECK: [[FMOVS0_:%[0-9]+]]:fpr32 = FMOVS0
; CHECK: FCMPSri [[COPY]], implicit-def $nzcv
; CHECK: [[FCSELSrrr:%[0-9]+]]:fpr32 = FCSELSrrr [[FMOVS0_]], [[COPY1]], 0, implicit $nzcv
; CHECK: FCMPSri [[COPY]], implicit-def $nzcv
; CHECK: [[FCSELSrrr1:%[0-9]+]]:fpr32 = FCSELSrrr [[COPY1]], [[FMOVS0_]], 0, implicit $nzcv
; CHECK: $s0 = COPY [[FCSELSrrr]]
; CHECK: $s1 = COPY [[FCSELSrrr1]]
; CHECK: RET_ReallyLR implicit $s0
%0:fpr(s32) = COPY $s0
%1:fpr(s32) = COPY $s1
%2:fpr(s32) = G_FCONSTANT float 0.000000e+00
%5:gpr(s32) = G_FCMP floatpred(oeq), %0(s32), %2
%3:gpr(s1) = G_TRUNC %5(s32)
%6:fpr(s1) = COPY %3(s1)
%4:fpr(s32) = G_SELECT %6(s1), %2, %1
%7:fpr(s32) = G_SELECT %6(s1), %1, %2
$s0 = COPY %4(s32)
$s1 = COPY %7(s32)
RET_ReallyLR implicit $s0
...
---
name: using_icmp