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[APInt] Use trailing bit counting methods instead of population count method in isAllOnesValue, isMaxSigendValue, and isMinSignedValue. NFCI 

The trailing bit methods will early out if they find a bit of the opposite while popcount must always look at all bits. I also assume that more CPUs implement trailing bit counting with native instructions than population count.

llvm-svn: 306154
This commit is contained in:
Craig Topper 2017-06-23 20:28:49 +00:00
parent 405165210b
commit b73646f822
1 changed files with 3 additions and 3 deletions
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6
llvm/include/llvm/ADT/APInt.h
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@ -389,7 +389,7 @@ public:
bool isAllOnesValue() const {
if (isSingleWord())
return U.VAL == WORD_MAX >> (APINT_BITS_PER_WORD - BitWidth);
return countPopulationSlowCase() == BitWidth;
return countTrailingOnesSlowCase() == BitWidth;
}
/// \brief Determine if all bits are clear
@ -414,7 +414,7 @@ public:
/// This checks to see if the value of this APInt is the maximum signed
/// value for the APInt's bit width.
bool isMaxSignedValue() const {
return !isNegative() && countPopulation() == BitWidth - 1;
return !isNegative() && countTrailingOnes() == BitWidth - 1;
}
/// \brief Determine if this is the smallest unsigned value.
@ -428,7 +428,7 @@ public:
/// This checks to see if the value of this APInt is the minimum signed
/// value for the APInt's bit width.
bool isMinSignedValue() const {
return isNegative() && isPowerOf2();
return isNegative() && countTrailingZeros() == BitWidth - 1;
}
/// \brief Check if this APInt has an N-bits unsigned integer value.