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[HashRecognize] Check TC against bitwidth of LHSAux #144881

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Merged
merged 3 commits into from
Jul 3, 2025
Merged

[HashRecognize] Check TC against bitwidth of LHSAux #144881

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b7f1192
[HashRecognize] Check TC against bitwidth of LHSAux
artagnon Jun 19, 2025
0d22e28
[HashRecognize] Add negative init.arg.excess.tc test
artagnon Jul 3, 2025
a9e2dbc
[HashRecognize] Fix excess.tc coverage
artagnon Jul 3, 2025
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29 changes: 15 additions & 14 deletions llvm/lib/Analysis/HashRecognize.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -247,16 +247,10 @@ KnownBits ValueEvolution::compute(const Value *V) {
}

bool ValueEvolution::computeEvolutions(ArrayRef<PhiStepPair> PhiEvolutions) {
for (unsigned I = 0; I < TripCount; ++I) {
for (auto [Phi, Step] : PhiEvolutions) {
KnownBits KnownAtIter = computeInstr(Step);
if (KnownAtIter.getBitWidth() < I + 1) {
ErrStr = "Loop iterations exceed bitwidth of result";
return false;
}
KnownPhis.emplace_or_assign(Phi, KnownAtIter);
}
}
for (unsigned I = 0; I < TripCount; ++I)
for (auto [Phi, Step] : PhiEvolutions)
KnownPhis.emplace_or_assign(Phi, computeInstr(Step));

return ErrStr.empty();
}

Expand Down Expand Up @@ -605,6 +599,13 @@ HashRecognize::recognizeCRC() const {
return "Recurrences not intertwined with XOR";
}

// Make sure that the TC doesn't exceed the bitwidth of LHSAux, or LHS.
Value *LHS = ConditionalRecurrence.Start;
Value *LHSAux = SimpleRecurrence ? SimpleRecurrence.Start : nullptr;
if (TC > (LHSAux ? LHSAux->getType()->getIntegerBitWidth()
: LHS->getType()->getIntegerBitWidth()))
return "Loop iterations exceed bitwidth of data";

// Make sure that the computed value is used in the exit block: this should be
// true even if it is only really used in an outer loop's exit block, since
// the loop is in LCSSA form.
Expand Down Expand Up @@ -633,13 +634,13 @@ HashRecognize::recognizeCRC() const {
return VE.getError();
KnownBits ResultBits = VE.KnownPhis.at(ConditionalRecurrence.Phi);

unsigned N = std::min(TC, ResultBits.getBitWidth());
auto IsZero = [](const KnownBits &K) { return K.isZero(); };
if (!checkExtractBits(ResultBits, TC, IsZero, *ByteOrderSwapped))
if (!checkExtractBits(ResultBits, N, IsZero, *ByteOrderSwapped))
return ErrBits(ResultBits, TC, *ByteOrderSwapped);

Value *LHSAux = SimpleRecurrence ? SimpleRecurrence.Start : nullptr;
return PolynomialInfo(TC, ConditionalRecurrence.Start, GenPoly, ComputedValue,
*ByteOrderSwapped, LHSAux);
return PolynomialInfo(TC, LHS, GenPoly, ComputedValue, *ByteOrderSwapped,
LHSAux);
}

void CRCTable::print(raw_ostream &OS) const {
Expand Down
64 changes: 54 additions & 10 deletions llvm/test/Analysis/HashRecognize/cyclic-redundancy-check.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -146,8 +146,28 @@ exit: ; preds = %loop

define i8 @crc8.le.tc16(i16 %msg, i8 %checksum) {
; CHECK-LABEL: 'crc8.le.tc16'
; CHECK-NEXT: Did not find a hash algorithm
; CHECK-NEXT: Reason: Loop iterations exceed bitwidth of result
; CHECK-NEXT: Found little-endian CRC-8 loop with trip count 16
; CHECK-NEXT: Initial CRC: i8 %checksum
; CHECK-NEXT: Generating polynomial: 29
; CHECK-NEXT: Computed CRC: %crc.next = select i1 %check.sb, i8 %crc.lshr, i8 %crc.xor
; CHECK-NEXT: Auxiliary data: i16 %msg
; CHECK-NEXT: Computed CRC lookup table:
; CHECK-NEXT: 0 9 18 27 31 22 13 4 5 12 23 30 26 19 8 1
; CHECK-NEXT: 10 3 24 17 21 28 7 14 15 6 29 20 16 25 2 11
; CHECK-NEXT: 20 29 6 15 11 2 25 16 17 24 3 10 14 7 28 21
; CHECK-NEXT: 30 23 12 5 1 8 19 26 27 18 9 0 4 13 22 31
; CHECK-NEXT: 19 26 1 8 12 5 30 23 22 31 4 13 9 0 27 18
; CHECK-NEXT: 25 16 11 2 6 15 20 29 28 21 14 7 3 10 17 24
; CHECK-NEXT: 7 14 21 28 24 17 10 3 2 11 16 25 29 20 15 6
; CHECK-NEXT: 13 4 31 22 18 27 0 9 8 1 26 19 23 30 5 12
; CHECK-NEXT: 29 20 15 6 2 11 16 25 24 17 10 3 7 14 21 28
; CHECK-NEXT: 23 30 5 12 8 1 26 19 18 27 0 9 13 4 31 22
; CHECK-NEXT: 9 0 27 18 22 31 4 13 12 5 30 23 19 26 1 8
; CHECK-NEXT: 3 10 17 24 28 21 14 7 6 15 20 29 25 16 11 2
; CHECK-NEXT: 14 7 28 21 17 24 3 10 11 2 25 16 20 29 6 15
; CHECK-NEXT: 4 13 22 31 27 18 9 0 1 8 19 26 30 23 12 5
; CHECK-NEXT: 26 19 8 1 5 12 23 30 31 22 13 4 0 9 18 27
; CHECK-NEXT: 16 25 2 11 15 6 29 20 21 28 7 14 10 3 24 17
;
entry:
br label %loop
Expand Down Expand Up @@ -676,27 +696,51 @@ exit: ; preds = %loop
ret i16 %crc.next
}

define i16 @not.crc.excess.tc(i16 %msg, i16 %checksum) {
define i16 @not.crc.excess.tc(i8 %msg, i16 %checksum) {
; CHECK-LABEL: 'not.crc.excess.tc'
; CHECK-NEXT: Did not find a hash algorithm
; CHECK-NEXT: Reason: Loop iterations exceed bitwidth of result
; CHECK-NEXT: Reason: Loop iterations exceed bitwidth of data
;
entry:
br label %loop

loop: ; preds = %loop, %entry
%iv = phi i8 [ 0, %entry ], [ %iv.next, %loop ]
%crc = phi i16 [ %checksum, %entry ], [ %crc.next, %loop ]
%data = phi i16 [ %msg, %entry ], [ %data.next, %loop ]
%xor.crc.data = xor i16 %crc, %data
%and.crc.data = and i16 %xor.crc.data, 1
%data.next = lshr i16 %data, 1
%check.sb = icmp eq i16 %and.crc.data, 0
%data = phi i8 [ %msg, %entry ], [ %data.next, %loop ]
%crc.trunc = trunc i16 %crc to i8
%xor.crc.data = xor i8 %crc.trunc, %data
%and.crc.data = and i8 %xor.crc.data, 1
%data.next = lshr i8 %data, 1
%check.sb = icmp eq i8 %and.crc.data, 0
%crc.lshr = lshr i16 %crc, 1
%crc.xor = xor i16 %crc.lshr, -24575
%crc.next = select i1 %check.sb, i16 %crc.lshr, i16 %crc.xor
%iv.next = add nuw nsw i8 %iv, 1
%exit.cond = icmp samesign ult i8 %iv, 31
%exit.cond = icmp samesign ult i8 %iv, 15
br i1 %exit.cond, label %loop, label %exit

exit: ; preds = %loop
ret i16 %crc.next
}

define i16 @not.crc.init.arg.excess.tc(i16 %crc.init) {
; CHECK-LABEL: 'not.crc.init.arg.excess.tc'
; CHECK-NEXT: Did not find a hash algorithm
; CHECK-NEXT: Reason: Loop iterations exceed bitwidth of data
;
entry:
br label %loop

loop: ; preds = %loop, %entry
%iv = phi i32 [ 0, %entry ], [ %iv.next, %loop ]
%crc = phi i16 [ %crc.init, %entry ], [ %crc.next, %loop ]
%crc.shl = shl i16 %crc, 1
%crc.xor = xor i16 %crc.shl, 4129
%check.sb = icmp slt i16 %crc, 0
%crc.next = select i1 %check.sb, i16 %crc.xor, i16 %crc.shl
%iv.next = add nuw nsw i32 %iv, 1
%exit.cond = icmp samesign ult i32 %iv, 31
br i1 %exit.cond, label %loop, label %exit

exit: ; preds = %loop
Expand Down
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