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[GlobalIsel] Add combine for select with constants #121088

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Merged
merged 1 commit into from
Jan 1, 2025
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[GlobalIsel] Add combine for select with constants #121088

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17 changes: 17 additions & 0 deletions llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -6823,6 +6823,23 @@ bool CombinerHelper::tryFoldSelectOfConstants(GSelect *Select,
};
return true;
}

// select Cond, 0, Pow2 --> (zext (!Cond)) << log2(Pow2)
if (FalseValue.isPowerOf2() && TrueValue.isZero()) {
MatchInfo = [=](MachineIRBuilder &B) {
B.setInstrAndDebugLoc(*Select);
Register Not = MRI.createGenericVirtualRegister(CondTy);
B.buildNot(Not, Cond);
Register Inner = MRI.createGenericVirtualRegister(TrueTy);
B.buildZExtOrTrunc(Inner, Not);
// The shift amount must be scalar.
LLT ShiftTy = TrueTy.isVector() ? TrueTy.getElementType() : TrueTy;
auto ShAmtC = B.buildConstant(ShiftTy, FalseValue.exactLogBase2());
B.buildShl(Dest, Inner, ShAmtC, Flags);
};
return true;
}

// select Cond, -1, C --> or (sext Cond), C
if (TrueValue.isAllOnes()) {
MatchInfo = [=](MachineIRBuilder &B) {
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30 changes: 30 additions & 0 deletions llvm/test/CodeGen/AArch64/GlobalISel/combine-select.mir
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Expand Up @@ -436,6 +436,36 @@ body: |
$w0 = COPY %ext(s32)
...
---
# select cond, 0, 64 --> (zext (!Cond)) << log2(Pow2)
name: select_cond_0_64_to_shift
body: |
bb.1:
liveins: $x0, $x1, $x2
; CHECK-LABEL: name: select_cond_0_64_to_shift
; CHECK: liveins: $x0, $x1, $x2
; CHECK-NEXT: {{ $}}
; CHECK-NEXT: [[COPY:%[0-9]+]]:_(s64) = COPY $x0
; CHECK-NEXT: %c:_(s1) = G_TRUNC [[COPY]](s64)
; CHECK-NEXT: [[C:%[0-9]+]]:_(s1) = G_CONSTANT i1 true
; CHECK-NEXT: [[XOR:%[0-9]+]]:_(s1) = G_XOR %c, [[C]]
; CHECK-NEXT: [[ZEXT:%[0-9]+]]:_(s8) = G_ZEXT [[XOR]](s1)
; CHECK-NEXT: [[C1:%[0-9]+]]:_(s8) = G_CONSTANT i8 6
; CHECK-NEXT: %sel:_(s8) = G_SHL [[ZEXT]], [[C1]](s8)
; CHECK-NEXT: %ext:_(s32) = G_ANYEXT %sel(s8)
; CHECK-NEXT: $w0 = COPY %ext(s32)
%0:_(s64) = COPY $x0
%1:_(s64) = COPY $x1
%2:_(s64) = COPY $x2
%c:_(s1) = G_TRUNC %0
%t:_(s1) = G_TRUNC %1
%f:_(s1) = G_TRUNC %2
%two:_(s8) = G_CONSTANT i8 0
%one:_(s8) = G_CONSTANT i8 64
%sel:_(s8) = G_SELECT %c, %two, %one
%ext:_(s32) = G_ANYEXT %sel
$w0 = COPY %ext(s32)
...
---
# select cond, -1, 0 --> sext Cond
name: select_cond_minus_1_0_to_sext_cond
body: |
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