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Switch on the use of arbitrary precision integers in scalar evolution. This will

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bail after 256-bits to avoid producing code that the backends can't handle.
Previously, we capped it at 64-bits, preferring to miscompile in those cases.

This change also reverts much of r52248 because the invariants the code was
expecting are now being met.

llvm-svn: 53812
This commit is contained in:
Nick Lewycky 2008-07-21 02:51:31 +00:00
parent f9ef4917c9
commit ea4a155439
1 changed files with 8 additions and 22 deletions
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30
lib/Analysis/ScalarEvolution.cpp
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@ -538,20 +538,12 @@ static SCEVHandle BinomialCoefficient(SCEVHandle It, unsigned K,
assert(K < 9 && "We cannot handle such long AddRecs yet.");
// FIXME: A temporary hack to remove in future. Arbitrary precision integers
// aren't supported by the code generator yet. For the dividend, the bitwidth
// we use is the smallest power of 2 greater or equal to K*W and less or equal
// to 64. Note that setting the upper bound for bitwidth may still lead to
// miscompilation in some cases.
unsigned DividendBits = 1U << Log2_32_Ceil(K * It->getBitWidth());
if (DividendBits > 64)
DividendBits = 64;
#if 0 // Waiting for the APInt support in the code generator...
unsigned DividendBits = K * It->getBitWidth();
#endif
if (DividendBits > 256)
return new SCEVCouldNotCompute();
const IntegerType *DividendTy = IntegerType::get(DividendBits);
const SCEVHandle ExIt = SE.getTruncateOrZeroExtend(It, DividendTy);
const SCEVHandle ExIt = SE.getZeroExtendExpr(It, DividendTy);
// The final number of bits we need to perform the division is the maximum of
// dividend and divisor bitwidths.
@ -573,12 +565,7 @@ static SCEVHandle BinomialCoefficient(SCEVHandle It, unsigned K,
Dividend *= N-(K-1);
if (DividendTy != DivisionTy)
Dividend = Dividend.zext(DivisionTy->getBitWidth());
APInt Result = Dividend.udiv(Divisor);
if (Result.getBitWidth() != It->getBitWidth())
Result = Result.trunc(It->getBitWidth());
return SE.getConstant(Result);
return SE.getConstant(Dividend.udiv(Divisor).trunc(It->getBitWidth()));
}
SCEVHandle Dividend = ExIt;
@ -587,11 +574,10 @@ static SCEVHandle BinomialCoefficient(SCEVHandle It, unsigned K,
SE.getMulExpr(Dividend,
SE.getMinusSCEV(ExIt, SE.getIntegerSCEV(i, DividendTy)));
return SE.getTruncateOrZeroExtend(
SE.getUDivExpr(
SE.getTruncateOrZeroExtend(Dividend, DivisionTy),
SE.getConstant(Divisor)
), It->getType());
if (DividendTy != DivisionTy)
Dividend = SE.getZeroExtendExpr(Dividend, DivisionTy);
return SE.getTruncateExpr(SE.getUDivExpr(Dividend, SE.getConstant(Divisor)),
It->getType());
}
/// evaluateAtIteration - Return the value of this chain of recurrences at