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reimplement truncate() to make it optimal.

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It is optimal at least up to 7 bits (I've tested all such cases)
This change to truncate() allows a little simplification to the multiplication code,
and it also makes multiplication optimal :)

llvm-svn: 160512
This commit is contained in:
Nuno Lopes 2012-07-19 16:27:45 +00:00
parent 72e0295e66
commit 324d91f181
1 changed files with 45 additions and 10 deletions
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55
lib/Support/ConstantRange.cpp
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@ -457,10 +457,53 @@ ConstantRange ConstantRange::signExtend(uint32_t DstTySize) const {
/// truncated to the specified type.
ConstantRange ConstantRange::truncate(uint32_t DstTySize) const {
assert(getBitWidth() > DstTySize && "Not a value truncation");
if (isFullSet() || getSetSize().getActiveBits() > DstTySize)
if (isEmptySet())
return ConstantRange(DstTySize, /*isFullSet=*/false);
if (isFullSet())
return ConstantRange(DstTySize, /*isFullSet=*/true);
return ConstantRange(Lower.trunc(DstTySize), Upper.trunc(DstTySize));
APInt MaxValue = APInt::getMaxValue(DstTySize).zext(getBitWidth());
APInt MaxBitValue(getBitWidth(), 0);
MaxBitValue.setBit(DstTySize);
APInt LowerDiv(Lower), UpperDiv(Upper);
ConstantRange Union(DstTySize, /*isFullSet=*/false);
// Analyze wrapped sets in their two parts: [0, Upper) \/ [Lower, MaxValue]
// We use the non-wrapped set code to analyze the [Lower, MaxValue) part, and
// then we do the union with [MaxValue, Upper)
if (isWrappedSet()) {
// if Upper is greater than Max Value, it covers the whole truncated range.
if (Upper.uge(MaxValue))
return ConstantRange(DstTySize, /*isFullSet=*/true);
Union = ConstantRange(APInt::getMaxValue(DstTySize),Upper.trunc(DstTySize));
UpperDiv = APInt::getMaxValue(getBitWidth());
// Union covers the MaxValue case, so return if the remaining range is just
// MaxValue.
if (LowerDiv == UpperDiv)
return Union;
}
// Chop off the most significant bits that are past the destination bitwidth.
if (LowerDiv.uge(MaxValue)) {
APInt Div(getBitWidth(), 0);
APInt::udivrem(LowerDiv, MaxBitValue, Div, LowerDiv);
UpperDiv = UpperDiv - MaxBitValue * Div;
}
if (UpperDiv.ule(MaxValue))
return ConstantRange(LowerDiv.trunc(DstTySize),
UpperDiv.trunc(DstTySize)).unionWith(Union);
// The truncated value wrapps around. Check if we can do better than fullset.
APInt UpperModulo = UpperDiv - MaxBitValue;
if (UpperModulo.ult(LowerDiv))
return ConstantRange(LowerDiv.trunc(DstTySize),
UpperModulo.trunc(DstTySize)).unionWith(Union);
return ConstantRange(DstTySize, /*isFullSet=*/true);
}
/// zextOrTrunc - make this range have the bit width given by \p DstTySize. The
@ -537,14 +580,6 @@ ConstantRange::multiply(const ConstantRange &Other) const {
if (isEmptySet() || Other.isEmptySet())
return ConstantRange(getBitWidth(), /*isFullSet=*/false);
// If any of the operands is zero, then the result is also zero.
if ((getSingleElement() && *getSingleElement() == 0) ||
(Other.getSingleElement() && *Other.getSingleElement() == 0))
return ConstantRange(APInt(getBitWidth(), 0));
if (isFullSet() || Other.isFullSet())
return ConstantRange(getBitWidth(), /*isFullSet=*/true);
APInt this_min = getUnsignedMin().zext(getBitWidth() * 2);
APInt this_max = getUnsignedMax().zext(getBitWidth() * 2);
APInt Other_min = Other.getUnsignedMin().zext(getBitWidth() * 2);