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optimize uadd(x, cst) into a comparison when the normal

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result is dead.  This is required for my next patch to not
regress the testsuite.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122181 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2010-12-19 19:35:32 +00:00
parent cc3029acdd
commit 26b482d7a7
2 changed files with 26 additions and 0 deletions
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16
lib/Transforms/InstCombine/InstCombineCalls.cpp
View File

@ -523,6 +523,21 @@ Instruction *InstCombiner::visitCallInst(CallInst &CI) {
return InsertValueInst::Create(Struct, Add, 0);
}
}
// If the normal result of the add is dead, and the RHS is a constant, we
// can transform this into a range comparison.
// overflow = uadd a, -4 --> overflow = icmp ugt a, 3
if (ConstantInt *CI = dyn_cast<ConstantInt>(RHS))
if (ExtractValueInst *EVI = dyn_cast<ExtractValueInst>(II->use_back()))
if (II->hasOneUse() && EVI->getNumIndices() == 1 && !EVI->use_empty() &&
*EVI->idx_begin() == 1) { // Extract of overflow result.
Builder->SetInsertPoint(EVI);
Value *R = Builder->CreateICmpUGT(LHS, ConstantExpr::getNot(CI));
R->takeName(EVI);
ReplaceInstUsesWith(*EVI, R);
return II;
}
}
// FALL THROUGH uadd into sadd
case Intrinsic::sadd_with_overflow:
@ -550,6 +565,7 @@ Instruction *InstCombiner::visitCallInst(CallInst &CI) {
return InsertValueInst::Create(Struct, II->getArgOperand(0), 0);
}
}
break;
case Intrinsic::usub_with_overflow:
case Intrinsic::ssub_with_overflow:

10
test/Transforms/InstCombine/intrinsics.ll
View File

@ -71,6 +71,16 @@ define i8 @uaddtest5(i8 %A, i1* %overflowPtr) {
; CHECK: ret i8 %A
}
define i1 @uaddtest6(i8 %A, i8 %B) {
%x = call %overflow.result @llvm.uadd.with.overflow.i8(i8 %A, i8 -4)
%z = extractvalue %overflow.result %x, 1
ret i1 %z
; CHECK: @uaddtest6
; CHECK-NEXT: %z = icmp ugt i8 %A, 3
; CHECK-NEXT: ret i1 %z
}
define i8 @umultest1(i8 %A, i1* %overflowPtr) {
%x = call %overflow.result @llvm.umul.with.overflow.i8(i8 0, i8 %A)
%y = extractvalue %overflow.result %x, 0