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[APInt] Add early outs for a division by 1 to udiv/urem/udivrem

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We already counted the number of bits in the RHS so its pretty cheap to just check if the RHS is 1.

Differential Revision: https://reviews.llvm.org/D33154

llvm-svn: 302953
This commit is contained in:
Craig Topper 2017-05-12 21:45:50 +00:00
parent ddcccb1617
commit e96d8395f4
1 changed files with 18 additions and 4 deletions
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22
lib/Support/APInt.cpp
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@ -1565,14 +1565,18 @@ APInt APInt::udiv(const APInt& RHS) const {
}
// Get some facts about the LHS and RHS number of bits and words
unsigned rhsWords = getNumWords(RHS.getActiveBits());
assert(rhsWords && "Divided by zero???");
unsigned lhsWords = getNumWords(getActiveBits());
unsigned rhsBits = RHS.getActiveBits();
unsigned rhsWords = getNumWords(rhsBits);
assert(rhsWords && "Divided by zero???");
// Deal with some degenerate cases
if (!lhsWords)
// 0 / X ===> 0
return APInt(BitWidth, 0);
if (rhsBits == 1)
// X / 1 ===> X
return *this;
if (lhsWords < rhsWords || this->ult(RHS))
// X / Y ===> 0, iff X < Y
return APInt(BitWidth, 0);
@ -1611,13 +1615,17 @@ APInt APInt::urem(const APInt& RHS) const {
unsigned lhsWords = getNumWords(getActiveBits());
// Get some facts about the RHS
unsigned rhsWords = getNumWords(RHS.getActiveBits());
unsigned rhsBits = RHS.getActiveBits();
unsigned rhsWords = getNumWords(rhsBits);
assert(rhsWords && "Performing remainder operation by zero ???");
// Check the degenerate cases
if (lhsWords == 0)
// 0 % Y ===> 0
return APInt(BitWidth, 0);
if (rhsBits == 1)
// X % 1 ===> 0
return APInt(BitWidth, 0);
if (lhsWords < rhsWords || this->ult(RHS))
// X % Y ===> X, iff X < Y
return *this;
@ -1662,7 +1670,8 @@ void APInt::udivrem(const APInt &LHS, const APInt &RHS,
// Get some size facts about the dividend and divisor
unsigned lhsWords = getNumWords(LHS.getActiveBits());
unsigned rhsWords = getNumWords(RHS.getActiveBits());
unsigned rhsBits = RHS.getActiveBits();
unsigned rhsWords = getNumWords(rhsBits);
assert(rhsWords && "Performing divrem operation by zero ???");
// Check the degenerate cases
@ -1672,6 +1681,11 @@ void APInt::udivrem(const APInt &LHS, const APInt &RHS,
return;
}
if (rhsBits == 1) {
Quotient = LHS; // X / 1 ===> X
Remainder = 0; // X % 1 ===> 0
}
if (lhsWords < rhsWords || LHS.ult(RHS)) {
Remainder = LHS; // X % Y ===> X, iff X < Y
Quotient = 0; // X / Y ===> 0, iff X < Y