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APInt: Simplify EqualSlowCase

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Previously the code used getActiveBits() to determine the highest set
bit of each APInt first. However doing so requires the same amount of
memory accesses as simply comparing both numbers right away.

Removing all the active bit checks leads to simpler code and is faster
in my benchmark.

Differential Revision: http://reviews.llvm.org/D16620

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@260447 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Matthias Braun
2016-02-10 22:13:10 +00:00
parent 7e57e07d4e
commit 6bf8999e3a
1 changed files with 2 additions and 15 deletions
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lib/Support/APInt.cpp
+2 -15
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@@ -490,21 +490,8 @@ APInt APInt::operator-(const APInt& RHS) const {
}
bool APInt::EqualSlowCase(const APInt& RHS) const {
// Get some facts about the number of bits used in the two operands.
unsigned n1 = getActiveBits();
unsigned n2 = RHS.getActiveBits();
// If the number of bits isn't the same, they aren't equal
if (n1 != n2)
return false;
// If the number of bits fits in a word, we only need to compare the low word.
if (n1 <= APINT_BITS_PER_WORD)
return pVal[0] == RHS.pVal[0];
// Otherwise, compare everything
for (int i = whichWord(n1 - 1); i >= 0; --i)
if (pVal[i] != RHS.pVal[i])
for (unsigned I = 0, NumWords = getNumWords(); I < NumWords; ++I)
if (pVal[I] != RHS.pVal[I])
return false;
return true;
}