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Revert "[BasicAA] Revert "Revert r218714 - Make better use of zext and sign information.""

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This reverts commit r219135 -- still causing miscompiles in SPEC it seems...

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219432 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Hal Finkel
2014-10-09 19:48:12 +00:00
parent 2b3bbbdf0c
commit adba582bc6
3 changed files with 2 additions and 129 deletions
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43
lib/Analysis/BasicAliasAnalysis.cpp
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@ -254,10 +254,7 @@ static Value *GetLinearExpression(Value *V, APInt &Scale, APInt &Offset,
Value *Result = GetLinearExpression(CastOp, Scale, Offset, Extension,
DL, Depth+1, AT, DT);
Scale = Scale.zext(OldWidth);
// We have to sign-extend even if Extension == EK_ZeroExt as we can't
// decompose a sign extension (i.e. zext(x - 1) != zext(x) - zext(-1)).
Offset = Offset.sext(OldWidth);
Offset = Offset.zext(OldWidth);
return Result;
}
@ -1058,38 +1055,8 @@ BasicAliasAnalysis::aliasGEP(const GEPOperator *GEP1, uint64_t V1Size,
// Grab the least significant bit set in any of the scales.
if (!GEP1VariableIndices.empty()) {
uint64_t Modulo = 0;
bool AllPositive = true;
for (unsigned i = 0, e = GEP1VariableIndices.size();
i != e && AllPositive; ++i) {
const Value *V = GEP1VariableIndices[i].V;
for (unsigned i = 0, e = GEP1VariableIndices.size(); i != e; ++i)
Modulo |= (uint64_t)GEP1VariableIndices[i].Scale;
bool SignKnownZero, SignKnownOne;
ComputeSignBit(
const_cast<Value *>(V),
SignKnownZero, SignKnownOne,
DL, 0, AT, nullptr, DT);
// Zero-extension widens the variable, and so forces the sign
// bit to zero.
bool IsZExt = GEP1VariableIndices[i].Extension == EK_ZeroExt;
SignKnownZero |= IsZExt;
SignKnownOne &= !IsZExt;
// If the variable begins with a zero then we know it's
// positive, regardless of whether the value is signed or
// unsigned.
int64_t Scale = GEP1VariableIndices[i].Scale;
AllPositive &=
(SignKnownZero && Scale >= 0) ||
(SignKnownOne && Scale < 0);
// If the Value is currently positive but could change in a cycle,
// then we can't guarantee it'll always br positive.
if (AllPositive && !isValueEqualInPotentialCycles(V, V))
AllPositive = false;
}
Modulo = Modulo ^ (Modulo & (Modulo - 1));
// We can compute the difference between the two addresses
@ -1099,12 +1066,6 @@ BasicAliasAnalysis::aliasGEP(const GEPOperator *GEP1, uint64_t V1Size,
if (V1Size != UnknownSize && V2Size != UnknownSize &&
ModOffset >= V2Size && V1Size <= Modulo - ModOffset)
return NoAlias;
// If we know all the variables are positive, then GEP1 >= GEP1BasePtr.
// If GEP1BasePtr > V2 (GEP1BaseOffset > 0) then we know the pointers
// don't alias if V2Size can fit in the gap between V2 and GEP1BasePtr.
if (AllPositive && GEP1BaseOffset > 0 && V2Size <= (uint64_t) GEP1BaseOffset)
return NoAlias;
}
// Statically, we can see that the base objects are the same, but the