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[GlobalISel]: Simplify udiv lowering by determining known zeros #89678

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Merged
merged 2 commits into from
Apr 24, 2024
Merged

[GlobalISel]: Simplify udiv lowering by determining known zeros #89678

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Pre-commit test (NFC)
AZero13 Apr 22, 2024
4cb7b54
[GlobalISel]: Simplify udiv lowering by determining known zeros
AZero13 Apr 22, 2024
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9 changes: 8 additions & 1 deletion llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -5069,6 +5069,9 @@ MachineInstr *CombinerHelper::buildUDivUsingMul(MachineInstr &MI) {
const unsigned EltBits = ScalarTy.getScalarSizeInBits();
LLT ShiftAmtTy = getTargetLowering().getPreferredShiftAmountTy(Ty);
LLT ScalarShiftAmtTy = ShiftAmtTy.getScalarType();

unsigned KnownLeadingZeros =
KB ? KB->getKnownBits(LHS).countMinLeadingZeros() : 0;
auto &MIB = Builder;

bool UseNPQ = false;
Expand All @@ -5086,8 +5089,12 @@ MachineInstr *CombinerHelper::buildUDivUsingMul(MachineInstr &MI) {
// at the end.
// TODO: Use undef values for divisor of 1.
if (!Divisor.isOne()) {

// UnsignedDivisionByConstantInfo doesn't work correctly if leading zeros
// in the dividend exceeds the leading zeros for the divisor.
UnsignedDivisionByConstantInfo magics =
UnsignedDivisionByConstantInfo::get(Divisor);
UnsignedDivisionByConstantInfo::get(
Divisor, std::min(KnownLeadingZeros, Divisor.countl_zero()));

Magic = std::move(magics.Magic);

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26 changes: 26 additions & 0 deletions llvm/test/CodeGen/AArch64/GlobalISel/combine-udiv.ll
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Expand Up @@ -243,3 +243,29 @@ define <8 x i16> @pr38477(<8 x i16> %a0) {
%1 = udiv <8 x i16> %a0, <i16 1, i16 119, i16 73, i16 -111, i16 -3, i16 118, i16 32, i16 31>
ret <8 x i16> %1
}

define i32 @udiv_div_by_180(i32 %x)
; SDAG-LABEL: udiv_div_by_180:
; SDAG: // %bb.0:
; SDAG-NEXT: mov w8, #5826 // =0x16c2
; SDAG-NEXT: and w9, w0, #0xff
; SDAG-NEXT: movk w8, #364, lsl #16
; SDAG-NEXT: umull x8, w9, w8
; SDAG-NEXT: lsr x0, x8, #32
; SDAG-NEXT: // kill: def $w0 killed $w0 killed $x0
; SDAG-NEXT: ret
;
; GISEL-LABEL: udiv_div_by_180:
; GISEL: // %bb.0:
; GISEL-NEXT: uxtb w8, w0
; GISEL-NEXT: mov w9, #5826 // =0x16c2
; GISEL-NEXT: movk w9, #364, lsl #16
; GISEL-NEXT: umull x8, w8, w9
; GISEL-NEXT: lsr x0, x8, #32
; GISEL-NEXT: // kill: def $w0 killed $w0 killed $x0
; GISEL-NEXT: ret
{
%truncate = and i32 %x, 255
%udiv = udiv i32 %truncate, 180
ret i32 %udiv
}
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