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PR19753: Optimize comparisons with "ashr exact" of a constanst.

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Patch by suyog sarda.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209903 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Rafael Espindola
2014-05-30 15:54:32 +00:00
parent 6319c0c520
commit fcb9926813
2 changed files with 25 additions and 0 deletions
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17
lib/Transforms/InstCombine/InstCombineCompares.cpp
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@@ -2439,6 +2439,23 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
return new ICmpInst(I.getPredicate(), A, B);
}
// PR19753:
// (icmp (ashr exact const2, A), const1) -> icmp A, Log2(const2/const1)
// Cases where const1 doesn't divide const2 exactly or Quotient is not
// exact of log2 are handled by SimplifyICmpInst call above where we
// return false.
// TODO: Handle this for lshr exact with udiv.
{
ConstantInt *CI2;
if (match(Op0, m_AShr(m_ConstantInt(CI2), m_Value(A))) &&
(cast<BinaryOperator>(Op0)->isExact())) {
APInt Quotient = CI2->getValue().sdiv(CI->getValue());
unsigned shift = Quotient.logBase2();
return new ICmpInst(I.getPredicate(), A,
ConstantInt::get(A->getType(), shift));
}
}
// If we have an icmp le or icmp ge instruction, turn it into the
// appropriate icmp lt or icmp gt instruction. This allows us to rely on
// them being folded in the code below. The SimplifyICmpInst code has