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Added support to optimize comparisons with "lshr exact" of a constant.

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Patch by Rahul Jain.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210040 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Rafael Espindola 2014-06-02 19:19:04 +00:00
parent f50e395308
commit 83223f52e7
2 changed files with 37 additions and 6 deletions
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35
lib/Transforms/InstCombine/InstCombineCompares.cpp
View File

@ -2318,6 +2318,32 @@ static bool swapMayExposeCSEOpportunities(const Value * Op0,
return GlobalSwapBenefits > 0;
}
// Helper function to check whether Op represents a lshr/ashr exact
// instruction. For example:
// (icmp (ashr exact const2, A), const1) -> icmp A, Log2(const2/const1)
// Here if Op represents -> (ashr exact const2, A), and CI represents
// const1, we compute Quotient as const2/const1.
static bool checkShrExact(Value *Op, APInt &Quotient, const ConstantInt *CI,
Value *&A) {
ConstantInt *CI2;
if (match(Op, m_AShr(m_ConstantInt(CI2), m_Value(A))) &&
(cast<BinaryOperator>(Op)->isExact())) {
Quotient = CI2->getValue().sdiv(CI->getValue());
return true;
}
// Handle the case for lhsr.
if (match(Op, m_LShr(m_ConstantInt(CI2), m_Value(A))) &&
(cast<BinaryOperator>(Op)->isExact())) {
Quotient = CI2->getValue().udiv(CI->getValue());
return true;
}
return false;
}
Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
bool Changed = false;
Value *Op0 = I.getOperand(0), *Op1 = I.getOperand(1);
@ -2443,13 +2469,10 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
// (icmp (ashr exact const2, A), const1) -> icmp A, Log2(const2/const1)
// Cases where const1 doesn't divide const2 exactly or Quotient is not
// exact of log2 are handled by SimplifyICmpInst call above where we
// return false.
// TODO: Handle this for lshr exact with udiv.
// return false. Similar for lshr.
{
ConstantInt *CI2;
if (match(Op0, m_AShr(m_ConstantInt(CI2), m_Value(A))) &&
(cast<BinaryOperator>(Op0)->isExact())) {
APInt Quotient = CI2->getValue().sdiv(CI->getValue());
APInt Quotient;
if (checkShrExact(Op0, Quotient, CI, A)) {
unsigned shift = Quotient.logBase2();
return new ICmpInst(I.getPredicate(), A,
ConstantInt::get(A->getType(), shift));

8
test/Transforms/InstCombine/icmp.ll
View File

@ -1390,3 +1390,11 @@ define i1 @exact_ashr_eq_false(i32 %a) {
%cmp = icmp eq i32 %shr, -15
ret i1 %cmp
}
; CHECK-LABEL: @exact_lhsr
; CHECK-NEXT: icmp eq i32 %a, 3
define i1 @exact_lhsr(i32 %a) {
%shr = lshr exact i32 80, %a
%cmp = icmp eq i32 %shr, 10
ret i1 %cmp
}