Commit 95a46333 authored by Hans Wennborg's avatar Hans Wennborg
Browse files

Merging r226023: 

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r226023 | majnemer | 2015-01-14 11:26:56 -0800 (Wed, 14 Jan 2015) | 3 lines

InstCombine: Don't take A-B<0 into A<B if A-B has other uses

This fixes PR22226.
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llvm-svn: 226059
parent 9d1ac804

llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp

+28 −26
Original line number Diff line number Diff line
@@ -2686,12 +2686,13 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) { 
        return Res;

    }



    // The following transforms are only 'worth it' if the only user of the

    // subtraction is the icmp.

    if (Op0->hasOneUse()) {

      // (icmp ne/eq (sub A B) 0) -> (icmp ne/eq A, B)

      if (I.isEquality() && CI->isZero() &&

        match(Op0, m_Sub(m_Value(A), m_Value(B)))) {

      // (icmp cond A B) if cond is equality

          match(Op0, m_Sub(m_Value(A), m_Value(B))))

        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() &&
@@ -2712,6 +2713,7 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) { 
      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

llvm/test/Transforms/InstCombine/icmp.ll

+15 −0
Original line number Diff line number Diff line
@@ -1558,3 +1558,18 @@ define i1 @f4(i64 %a, i64 %b) { 
  %v = icmp sle i64 %t, 0

  ret i1 %v

}



; CHECK-LABEL: @f5

; CHECK: %[[cmp:.*]] = icmp slt i32 %[[sub:.*]], 0

; CHECK: %[[neg:.*]] = sub nsw i32 0, %[[sub]]

; CHECK: %[[sel:.*]] = select i1 %[[cmp]], i32 %[[neg]], i32 %[[sub]]

; CHECK: ret i32 %[[sel]]

define i32 @f5(i8 %a, i8 %b) {

  %conv = zext i8 %a to i32

  %conv3 = zext i8 %b to i32

  %sub = sub nsw i32 %conv, %conv3

  %cmp4 = icmp slt i32 %sub, 0

  %sub7 = sub nsw i32 0, %sub

  %sub7.sub = select i1 %cmp4, i32 %sub7, i32 %sub

  ret i32 %sub7.sub

}