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[DSE] Add tryToShortenBegin support for memcpy #115314

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[DSE] Add tryToShortenBegin support for memcpy #115314

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29 changes: 26 additions & 3 deletions llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -203,9 +203,23 @@ static bool isShortenableAtTheEnd(Instruction *I) {
/// Returns true if the beginning of this instruction can be safely shortened
/// in length.
static bool isShortenableAtTheBeginning(Instruction *I) {
// FIXME: Handle only memset for now. Supporting memcpy/memmove should be
// easily done by offsetting the source address.
return isa<AnyMemSetInst>(I);
if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(I)) {
switch (II->getIntrinsicID()) {
default:
return false;
case Intrinsic::memset:
case Intrinsic::memcpy:
case Intrinsic::memset_inline:
case Intrinsic::memcpy_inline:
case Intrinsic::memcpy_element_unordered_atomic:
case Intrinsic::memset_element_unordered_atomic:
// Do shorten memory intrinsics.
// FIXME: Add memmove if it's also safe to transform.
return true;
}
}

return false;
}

static std::optional<TypeSize> getPointerSize(const Value *V,
Expand Down Expand Up @@ -644,6 +658,15 @@ static bool tryToShorten(Instruction *DeadI, int64_t &DeadStart,
DeadI->getIterator());
NewDestGEP->setDebugLoc(DeadIntrinsic->getDebugLoc());
DeadIntrinsic->setDest(NewDestGEP);

if (auto *MTI = dyn_cast<AnyMemTransferInst>(DeadIntrinsic)) {
Instruction *NewSrcGEP = GetElementPtrInst::CreateInBounds(
Type::getInt8Ty(DeadIntrinsic->getContext()), MTI->getRawSource(),
Indices, "", DeadI->getIterator());
NewSrcGEP->setDebugLoc(DeadIntrinsic->getDebugLoc());
MTI->setSource(NewSrcGEP);
MTI->setSourceAlignment(PrefAlign);
}
}

// Update attached dbg.assign intrinsics. Assume 8-bit byte.
Expand Down
4 changes: 3 additions & 1 deletion llvm/test/Transforms/DeadStoreElimination/libcalls-chk.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -130,7 +130,9 @@ define void @dse_strncpy_memcpy_chk_test2(ptr noalias %out, ptr noalias %in, i64

define void @test_memcpy_intrinsic_and_memcpy_chk(ptr %A, ptr %B, ptr noalias %C) {
; CHECK-LABEL: @test_memcpy_intrinsic_and_memcpy_chk(
; CHECK-NEXT: tail call void @llvm.memcpy.p0.p0.i64(ptr [[A:%.*]], ptr [[B:%.*]], i64 48, i1 false)
; CHECK-NEXT: [[TMP1:%.*]] = getelementptr inbounds i8, ptr [[A:%.*]], i64 1
; CHECK-NEXT: [[TMP2:%.*]] = getelementptr inbounds i8, ptr [[B:%.*]], i64 1
; CHECK-NEXT: tail call void @llvm.memcpy.p0.p0.i64(ptr align 1 [[TMP1]], ptr align 1 [[TMP2]], i64 47, i1 false)
; CHECK-NEXT: [[CALL:%.*]] = call ptr @__memcpy_chk(ptr [[A]], ptr [[C:%.*]], i64 1, i64 10)
; CHECK-NEXT: ret void
;
Expand Down