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[InstCombine] Drop Range attribute when simplifying 'fshl' based on demanded bits #124429

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Merged
merged 1 commit into from
Jan 25, 2025
+8 −4
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[InstCombine] Drop Range attribute when simplifying 'fshl' based on demanded bits #124429

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9 changes: 6 additions & 3 deletions llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1039,11 +1039,14 @@ Value *InstCombinerImpl::SimplifyDemandedUseBits(Instruction *I,
APInt DemandedMaskLHS(DemandedMask.lshr(ShiftAmt));
APInt DemandedMaskRHS(DemandedMask.shl(BitWidth - ShiftAmt));
if (I->getOperand(0) != I->getOperand(1)) {
if (SimplifyDemandedBits(I, 0, DemandedMaskLHS, LHSKnown,
Depth + 1, Q) ||
if (SimplifyDemandedBits(I, 0, DemandedMaskLHS, LHSKnown, Depth + 1,
Q) ||
SimplifyDemandedBits(I, 1, DemandedMaskRHS, RHSKnown, Depth + 1,
Q))
Q)) {
// Range attribute may no longer hold.
I->dropPoisonGeneratingReturnAttributes();
return I;
}
} else { // fshl is a rotate
// Avoid converting rotate into funnel shift.
// Only simplify if one operand is constant.
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3 changes: 2 additions & 1 deletion llvm/test/Transforms/InstCombine/fsh.ll
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Expand Up @@ -1069,11 +1069,12 @@ entry:
ret <2 x i31> %res
}

;; Issue #124387 Range attribute no longer holds after operands changed.
define i8 @fshl_range_trunc(i1 %x) {
; CHECK-LABEL: @fshl_range_trunc(
; CHECK-NEXT: [[ZEXT:%.*]] = zext i1 [[X:%.*]] to i32
; CHECK-NEXT: [[OR:%.*]] = or disjoint i32 [[ZEXT]], 126
; CHECK-NEXT: [[FSHL:%.*]] = call range(i32 -4, 2) i32 @llvm.fshl.i32(i32 [[OR]], i32 -2, i32 1)
; CHECK-NEXT: [[FSHL:%.*]] = call i32 @llvm.fshl.i32(i32 [[OR]], i32 -2, i32 1)
; CHECK-NEXT: [[TR:%.*]] = trunc nuw i32 [[FSHL]] to i8
; CHECK-NEXT: ret i8 [[TR]]
;
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