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PR19753: Optimize comparisons with "ashr exact" of a constanst.
Patch by suyog sarda. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209903 91177308-0d34-0410-b5e6-96231b3b80d8
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@ -2439,6 +2439,23 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
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return new ICmpInst(I.getPredicate(), A, B);
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}
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// PR19753:
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// (icmp (ashr exact const2, A), const1) -> icmp A, Log2(const2/const1)
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// Cases where const1 doesn't divide const2 exactly or Quotient is not
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// exact of log2 are handled by SimplifyICmpInst call above where we
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// return false.
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// TODO: Handle this for lshr exact with udiv.
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{
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ConstantInt *CI2;
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if (match(Op0, m_AShr(m_ConstantInt(CI2), m_Value(A))) &&
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(cast<BinaryOperator>(Op0)->isExact())) {
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APInt Quotient = CI2->getValue().sdiv(CI->getValue());
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unsigned shift = Quotient.logBase2();
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return new ICmpInst(I.getPredicate(), A,
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ConstantInt::get(A->getType(), shift));
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}
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}
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// If we have an icmp le or icmp ge instruction, turn it into the
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// appropriate icmp lt or icmp gt instruction. This allows us to rely on
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// them being folded in the code below. The SimplifyICmpInst code has
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@ -1365,3 +1365,11 @@ define i1 @icmp_neg_cst_slt(i32 %a) {
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%2 = icmp slt i32 %1, -10
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ret i1 %2
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}
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; CHECK-LABEL: @exact_ashr_eq_false
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; CHECK-NEXT: icmp eq i32 %a, 1
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define i1 @exact_ashr_eq_false(i32 %a) {
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%shr = ashr exact i32 -30, %a
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%cmp = icmp eq i32 %shr, -15
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ret i1 %cmp
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}
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