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[ValueTracking] Bail out on x86_fp80 when computing fpclass with knownbits #130477

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Merged
merged 2 commits into from
Mar 9, 2025
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[ValueTracking] Bail out on x86_fp80 when computing fpclass with knownbits #130477

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d037089
[InstSimplify] Add pre-commit tests. NFC.
dtcxzyw Mar 9, 2025
47c7bb1
[ValueTracking] Bail out on x86_fp80 when computing fpclass with know…
dtcxzyw Mar 9, 2025
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3 changes: 2 additions & 1 deletion llvm/lib/Analysis/ValueTracking.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -6208,13 +6208,14 @@ void computeKnownFPClass(const Value *V, const APInt &DemandedElts,
else if (Bits.isNegative())
Known.signBitMustBeOne();

if (Ty->isIEEE()) {
if (Ty->isIEEELikeFPTy()) {
// IEEE floats are NaN when all bits of the exponent plus at least one of
// the fraction bits are 1. This means:
// - If we assume unknown bits are 0 and the value is NaN, it will
// always be NaN
// - If we assume unknown bits are 1 and the value is not NaN, it can
// never be NaN
// Note: They do not hold for x86_fp80 format.
if (APFloat(Ty->getFltSemantics(), Bits.One).isNaN())
Known.KnownFPClasses = fcNan;
else if (!APFloat(Ty->getFltSemantics(), ~Bits.Zero).isNaN())
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17 changes: 17 additions & 0 deletions llvm/test/Transforms/InstSimplify/fcmp.ll
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Expand Up @@ -16,3 +16,20 @@ define i1 @poison2(float %x) {
%v = fcmp ueq float %x, poison
ret i1 %v
}

define i1 @pr130408(x86_fp80 %x) {
; CHECK-LABEL: @pr130408(
; CHECK-NEXT: [[BITS:%.*]] = bitcast x86_fp80 [[X:%.*]] to i80
; CHECK-NEXT: [[MASKED:%.*]] = and i80 [[BITS]], -604444463063240877801473
; CHECK-NEXT: [[OR:%.*]] = or i80 [[MASKED]], 302194561415509874573312
; CHECK-NEXT: [[FP:%.*]] = bitcast i80 [[OR]] to x86_fp80
; CHECK-NEXT: [[RES:%.*]] = fcmp uno x86_fp80 [[FP]], 0xK00000000000000000000
; CHECK-NEXT: ret i1 [[RES]]
;
%bits = bitcast x86_fp80 %x to i80
%masked = and i80 %bits, -604444463063240877801473
%or = or i80 %masked, 302194561415509874573312
%fp = bitcast i80 %or to x86_fp80
%res = fcmp uno x86_fp80 %fp, 0xK00000000000000000000
ret i1 %res
}
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