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

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This fixes PR22226.

llvm-svn: 226023
This commit is contained in:
David Majnemer 2015-01-14 19:26:56 +00:00
parent 24f46a1c22
commit b89ab3fd88
2 changed files with 42 additions and 25 deletions
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52
lib/Transforms/InstCombine/InstCombineCompares.cpp
View File

@ -2686,33 +2686,35 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
return Res;
}
// (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
return new ICmpInst(I.getPredicate(), A, B);
// 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))))
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);
}
// (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

15
test/Transforms/InstCombine/icmp.ll
View File

@ -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
}