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InstCombine: try to transform A-B < 0 into A < B

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We are allowed to move the 'B' to the right hand side if we an prove
there is no signed overflow and if the comparison itself is signed.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@225034 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
David Majnemer
2014-12-31 04:21:41 +00:00
parent c0319dd9c2
commit 0f77ccd6bb
2 changed files with 56 additions and 0 deletions
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lib/Transforms/InstCombine/InstCombineCompares.cpp
+20
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@@ -2692,6 +2692,26 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
return new ICmpInst(I.getPredicate(), A, B);
}
// (icmp sgt (sub nsw A B), -1) -> (icmp sge A, B)
if (I.getPredicate() == ICmpInst::ICMP_SGT && CI->isAllOnesValue() &&
match(Op0, m_NSWSub(m_Value(A), m_Value(B))))
return new ICmpInst(ICmpInst::ICMP_SGE, A, B);
// (icmp sgt (sub nsw A B), 0) -> (icmp sgt A, B)
if (I.getPredicate() == ICmpInst::ICMP_SGT && CI->isZero() &&
match(Op0, m_NSWSub(m_Value(A), m_Value(B))))
return new ICmpInst(ICmpInst::ICMP_SGT, A, B);
// (icmp slt (sub nsw A B), 0) -> (icmp slt A, B)
if (I.getPredicate() == ICmpInst::ICMP_SLT && CI->isZero() &&
match(Op0, m_NSWSub(m_Value(A), m_Value(B))))
return new ICmpInst(ICmpInst::ICMP_SLT, A, B);
// (icmp slt (sub nsw A B), 1) -> (icmp sle A, B)
if (I.getPredicate() == ICmpInst::ICMP_SLT && CI->isOne() &&
match(Op0, m_NSWSub(m_Value(A), m_Value(B))))
return new ICmpInst(ICmpInst::ICMP_SLE, A, B);
// 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