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InstCombine: Strength reduce sadd.with.overflow into a regular nsw add if we can prove that it cannot overflow.

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PR20194

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@212331 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Benjamin Kramer 2014-07-04 10:22:21 +00:00
parent a39d3ab819
commit 9c1df9164c
2 changed files with 28 additions and 0 deletions
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15
lib/Transforms/InstCombine/InstCombineCalls.cpp
View File

@ -421,6 +421,21 @@ Instruction *InstCombiner::visitCallInst(CallInst &CI) {
return InsertValueInst::Create(Struct, II->getArgOperand(0), 0);
}
}
// We can strength reduce reduce this signed add into a regular add if we
// can prove that it will never overflow.
if (II->getIntrinsicID() == Intrinsic::sadd_with_overflow) {
Value *LHS = II->getArgOperand(0), *RHS = II->getArgOperand(1);
if (WillNotOverflowSignedAdd(LHS, RHS)) {
Value *Add = Builder->CreateNSWAdd(LHS, RHS);
Add->takeName(&CI);
Constant *V[] = {UndefValue::get(Add->getType()), Builder->getFalse()};
StructType *ST = cast<StructType>(II->getType());
Constant *Struct = ConstantStruct::get(ST, V);
return InsertValueInst::Create(Struct, Add, 0);
}
}
break;
case Intrinsic::usub_with_overflow:
case Intrinsic::ssub_with_overflow:

13
test/Transforms/InstCombine/intrinsics.ll
View File

@ -3,6 +3,7 @@
%overflow.result = type {i8, i1}
declare %overflow.result @llvm.uadd.with.overflow.i8(i8, i8)
declare { i32, i1 } @llvm.sadd.with.overflow.i32(i32, i32)
declare %overflow.result @llvm.umul.with.overflow.i8(i8, i8)
declare double @llvm.powi.f64(double, i32) nounwind readonly
declare i32 @llvm.cttz.i32(i32, i1) nounwind readnone
@ -89,6 +90,18 @@ define i8 @uaddtest7(i8 %A, i8 %B) {
; CHECK-NEXT: ret i8 %z
}
; PR20194
define { i32, i1 } @saddtest1(i8 %a, i8 %b) {
%A = sext i8 %a to i32
%B = sext i8 %b to i32
%x = call { i32, i1 } @llvm.sadd.with.overflow.i32(i32 %A, i32 %B)
ret { i32, i1 } %x
; CHECK-LABEL: @saddtest1
; CHECK: %x = add nsw i32 %A, %B
; CHECK-NEXT: %1 = insertvalue { i32, i1 } { i32 undef, i1 false }, i32 %x, 0
; CHECK-NEXT: ret { i32, i1 } %1
}
define i8 @umultest1(i8 %A, i1* %overflowPtr) {
%x = call %overflow.result @llvm.umul.with.overflow.i8(i8 0, i8 %A)