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Optimize "icmp pred (urem X, Y), Y" --> true/false depending on pred. There's

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more work to do here, "icmp ult (urem X, 10), 11" doesn't optimize away yet.
Fixes example 3 from PR9343!


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@126741 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Nick Lewycky 2011-03-01 08:15:50 +00:00
parent 9d40193d79
commit 88cd0aadb2
2 changed files with 34 additions and 0 deletions
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18
lib/Analysis/InstructionSimplify.cpp
View File

@ -1434,6 +1434,9 @@ static Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
return ConstantInt::getTrue(CI->getContext());
break;
}
// TODO: integer div and rem with constant RHS all produce values in a
// constant range. We should check whether the comparison is a tautology.
}
// Compare of cast, for example (zext X) != 0 -> X != 0
@ -1644,6 +1647,21 @@ static Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
}
}
if (LBO && match(LBO, m_URem(m_Value(), m_Specific(RHS)))) {
switch (Pred) {
default:
break;
case ICmpInst::ICMP_EQ:
case ICmpInst::ICMP_UGT:
case ICmpInst::ICMP_UGE:
return ConstantInt::getFalse(RHS->getContext());
case ICmpInst::ICMP_NE:
case ICmpInst::ICMP_ULT:
case ICmpInst::ICMP_ULE:
return ConstantInt::getTrue(RHS->getContext());
}
}
// If the comparison is with the result of a select instruction, check whether
// comparing with either branch of the select always yields the same value.
if (isa<SelectInst>(LHS) || isa<SelectInst>(RHS))

16
test/Transforms/InstSimplify/compare.ll
View File

@ -187,3 +187,19 @@ define i1 @select4(i1 %cond) {
ret i1 %c
; CHECK: ret i1 %cond
}
define i1 @urem1(i32 %X, i32 %Y) {
; CHECK: @urem1
%A = urem i32 %X, %Y
%B = icmp ult i32 %A, %Y
ret i1 %B
; CHECK: ret i1 true
}
define i1 @urem2(i32 %X, i32 %Y) {
; CHECK: @urem2
%A = urem i32 %X, %Y
%B = icmp eq i32 %A, %Y
ret i1 %B
; CHECK ret i1 false
}