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InstSimplify: Optimize using dividend in sdiv

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Summary:
The dividend in an sdiv tells us the largest and smallest possible
results.  Use this fact to optimize comparisons against an sdiv with a
constant dividend.

Reviewers: nicholas

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D3795

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208999 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
David Majnemer 2014-05-16 16:57:04 +00:00
parent 18fc3275c1
commit 7a2ed26563
2 changed files with 13 additions and 0 deletions
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4
lib/Analysis/InstructionSimplify.cpp
View File

@ -2020,6 +2020,10 @@ static Value *SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
APInt NegOne = APInt::getAllOnesValue(Width);
if (!CI2->isZero())
Upper = NegOne.udiv(CI2->getValue()) + 1;
} else if (match(LHS, m_SDiv(m_ConstantInt(CI2), m_Value()))) {
// 'sdiv CI2, x' produces [-|CI2|, |CI2|].
Upper = CI2->getValue().abs() + 1;
Lower = (-Upper) + 1;
} else if (match(LHS, m_SDiv(m_Value(), m_ConstantInt(CI2)))) {
// 'sdiv x, CI2' produces [INT_MIN / CI2, INT_MAX / CI2].
APInt IntMin = APInt::getSignedMinValue(Width);

9
test/Transforms/InstSimplify/compare.ll
View File

@ -817,3 +817,12 @@ define i1 @compare_always_false_ne(i16 %a) {
; CHECK-LABEL: @compare_always_false_ne
; CHECK-NEXT: ret i1 true
}
define i1 @compare_dividend(i32 %a) {
%div = sdiv i32 2, %a
%cmp = icmp eq i32 %div, 3
ret i1 %cmp
; CHECK-LABEL: @compare_dividend
; CHECK-NEXT: ret i1 false
}