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[JumpThreading][GVN] Copy metadata when inserting preload into preds #134403

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[JumpThreading][GVN] Copy metadata when inserting preload into preds #134403

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447ccd2
[JumpThreading] Copy metadata when inserting preload into preds
dtcxzyw Apr 4, 2025
763c584
[JumpThreading][GVN] Use `copyMetadataForLoad`
dtcxzyw Apr 17, 2025
673ab49
[JumpThreading] Add tests. NFC.
dtcxzyw Apr 18, 2025
89b09c8
[GVN][JumpThreading] Address review comments
dtcxzyw Apr 23, 2025
544f796
[GVN][JumpThreading] Try to salvage UB-implying metadata
dtcxzyw Apr 23, 2025
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[GVN][JumpThreading] Try to salvage UB-implying metadata
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@dtcxzyw
dtcxzyw committed Apr 23, 2025
commit 544f796aaf9c89e474928a3cca24c95647c09eb1
20 changes: 17 additions & 3 deletions llvm/lib/Transforms/Scalar/GVN.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1517,9 +1517,23 @@ void GVNPass::eliminatePartiallyRedundantLoad(
}

NewLoad->copyMetadata(*Load);
// Drop UB-implying metadata as we do not know if it is guaranteed to
// transfer the execution to the original load.
NewLoad->dropUBImplyingAttrsAndMetadata();
std::optional<bool> TransfersExecution = std::nullopt;
NewLoad->eraseMetadataIf([&](unsigned Kind, const MDNode *MD) {
if (Kind == LLVMContext::MD_dbg || Kind == LLVMContext::MD_annotation)
return false;
if (is_contained(Metadata::PoisonGeneratingIDs, Kind))
return false;
// Try to salvage UB-implying metadata if we know it is guaranteed to
// transfer the execution to the original load.
if (!TransfersExecution.has_value()) {
// TEST ONLY
assert(
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I am not sure if it holds for GVN.

is_contained(successors(NewLoad->getParent()), Load->getParent()));
TransfersExecution = isGuaranteedToTransferExecutionToSuccessor(
Load->getParent()->begin(), Load->getIterator());
}
return !*TransfersExecution;
});

// Add the newly created load.
ValuesPerBlock.push_back(
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24 changes: 16 additions & 8 deletions llvm/lib/Transforms/Scalar/JumpThreading.cpp
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Expand Up @@ -1362,12 +1362,12 @@ bool JumpThreadingPass::simplifyPartiallyRedundantLoad(LoadInst *LoadI) {
// farther than to a predecessor, we need to reuse the code from GVN's PRE.
// It requires domination tree analysis, so for this simple case it is an
// overkill.
bool TransfersExecution = false;
std::optional<bool> TransfersExecution = std::nullopt;
if (PredsScanned.size() != AvailablePreds.size() &&
!isSafeToSpeculativelyExecute(LoadI)) {
for (auto I = LoadBB->begin(); &*I != LoadI; ++I)
if (!isGuaranteedToTransferExecutionToSuccessor(&*I))
return false;
if (!isGuaranteedToTransferExecutionToSuccessor(LoadBB->begin(),
LoadI->getIterator()))
return false;
TransfersExecution = true;
}

Expand Down Expand Up @@ -1411,10 +1411,18 @@ bool JumpThreadingPass::simplifyPartiallyRedundantLoad(LoadInst *LoadI) {
UnavailablePred->getTerminator()->getIterator());
NewVal->setDebugLoc(LoadI->getDebugLoc());
NewVal->copyMetadata(*LoadI);
// Drop UB-implying metadata if we do not know it is guaranteed to transfer
// the execution to the original load.
if (!TransfersExecution)
NewVal->dropUBImplyingAttrsAndMetadata();
NewVal->eraseMetadataIf([&](unsigned Kind, const MDNode *MD) {
if (Kind == LLVMContext::MD_dbg || Kind == LLVMContext::MD_annotation)
return false;
if (is_contained(Metadata::PoisonGeneratingIDs, Kind))
return false;
// Try to salvage UB-implying metadata if we know it is guaranteed to
// transfer the execution to the original load.
if (!TransfersExecution.has_value())
TransfersExecution = isGuaranteedToTransferExecutionToSuccessor(
LoadBB->begin(), LoadI->getIterator());
return !*TransfersExecution;
});

AvailablePreds.emplace_back(UnavailablePred, NewVal);
}
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18 changes: 11 additions & 7 deletions llvm/test/Transforms/GVN/pr64598.ll
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Expand Up @@ -6,20 +6,23 @@ define i32 @main(i64 %x, ptr %d, ptr noalias %p) {
; CHECK-SAME: (i64 [[X:%.*]], ptr [[D:%.*]], ptr noalias [[P:%.*]]) {
; CHECK-NEXT: entry:
; CHECK-NEXT: [[T1_PRE_PRE_PRE:%.*]] = load ptr, ptr [[P]], align 8
; CHECK-NEXT: [[T2_PRE_PRE_PRE:%.*]] = load ptr, ptr [[T1_PRE_PRE_PRE]], align 8
; CHECK-NEXT: [[T2_PRE_PRE_PRE:%.*]] = load ptr, ptr [[T1_PRE_PRE_PRE]], align 8, !tbaa [[TBAA0:![0-9]+]]
; CHECK-NEXT: [[T3_PRE_PRE_PRE:%.*]] = load ptr, ptr [[T2_PRE_PRE_PRE]], align 8
; CHECK-NEXT: br label [[LOOP:%.*]]
; CHECK: loop:
; CHECK-NEXT: [[T1_PRE_PRE:%.*]] = phi ptr [ [[T1_PRE_PRE19:%.*]], [[LOOP_LATCH:%.*]] ], [ [[T1_PRE_PRE_PRE]], [[ENTRY:%.*]] ]
; CHECK-NEXT: [[T2_PRE_PRE:%.*]] = phi ptr [ [[T2_PRE_PRE23:%.*]], [[LOOP_LATCH:%.*]] ], [ [[T2_PRE_PRE_PRE]], [[ENTRY:%.*]] ]
; CHECK-NEXT: [[T1_PRE_PRE:%.*]] = phi ptr [ [[T1_PRE_PRE19:%.*]], [[LOOP_LATCH]] ], [ [[T1_PRE_PRE_PRE]], [[ENTRY]] ]
; CHECK-NEXT: br label [[LOOP2:%.*]]
; CHECK: loop2:
; CHECK-NEXT: [[T1_PRE_PRE21:%.*]] = phi ptr [ [[T1_PRE_PRE19]], [[LOOP2_LATCH_LOOP2_CRIT_EDGE:%.*]] ], [ [[T1_PRE_PRE]], [[LOOP]] ]
; CHECK-NEXT: [[T2_PRE_PRE25:%.*]] = phi ptr [ [[T2_PRE_PRE23]], [[LOOP2_LATCH_LOOP2_CRIT_EDGE:%.*]] ], [ [[T2_PRE_PRE]], [[LOOP]] ]
; CHECK-NEXT: [[T1_PRE_PRE21:%.*]] = phi ptr [ [[T1_PRE_PRE19]], [[LOOP2_LATCH_LOOP2_CRIT_EDGE]] ], [ [[T1_PRE_PRE]], [[LOOP]] ]
; CHECK-NEXT: [[T3_PRE:%.*]] = phi ptr [ [[T3_PRE16:%.*]], [[LOOP2_LATCH_LOOP2_CRIT_EDGE]] ], [ [[T3_PRE_PRE_PRE]], [[LOOP]] ]
; CHECK-NEXT: [[T2_PRE:%.*]] = phi ptr [ [[T2_PRE13:%.*]], [[LOOP2_LATCH_LOOP2_CRIT_EDGE]] ], [ [[T2_PRE_PRE_PRE]], [[LOOP]] ]
; CHECK-NEXT: [[T2_PRE:%.*]] = phi ptr [ [[T2_PRE13:%.*]], [[LOOP2_LATCH_LOOP2_CRIT_EDGE]] ], [ [[T2_PRE_PRE]], [[LOOP]] ]
; CHECK-NEXT: [[T1_PRE:%.*]] = phi ptr [ [[T1_PRE10:%.*]], [[LOOP2_LATCH_LOOP2_CRIT_EDGE]] ], [ [[T1_PRE_PRE]], [[LOOP]] ]
; CHECK-NEXT: br label [[LOOP3:%.*]]
; CHECK: loop3:
; CHECK-NEXT: [[T1_PRE_PRE20:%.*]] = phi ptr [ [[T1_PRE_PRE19]], [[LOOP3_LATCH:%.*]] ], [ [[T1_PRE_PRE21]], [[LOOP2]] ]
; CHECK-NEXT: [[T2_PRE_PRE24:%.*]] = phi ptr [ [[T2_PRE_PRE23]], [[LOOP3_LATCH:%.*]] ], [ [[T2_PRE_PRE25]], [[LOOP2]] ]
; CHECK-NEXT: [[T1_PRE_PRE20:%.*]] = phi ptr [ [[T1_PRE_PRE19]], [[LOOP3_LATCH]] ], [ [[T1_PRE_PRE21]], [[LOOP2]] ]
; CHECK-NEXT: [[T3_PRE17:%.*]] = phi ptr [ [[T3_PRE16]], [[LOOP3_LATCH]] ], [ [[T3_PRE]], [[LOOP2]] ]
; CHECK-NEXT: [[T2_PRE14:%.*]] = phi ptr [ [[T2_PRE13]], [[LOOP3_LATCH]] ], [ [[T2_PRE]], [[LOOP2]] ]
; CHECK-NEXT: [[T1_PRE11:%.*]] = phi ptr [ [[T1_PRE10]], [[LOOP3_LATCH]] ], [ [[T1_PRE]], [[LOOP2]] ]
Expand All @@ -33,10 +36,11 @@ define i32 @main(i64 %x, ptr %d, ptr noalias %p) {
; CHECK: for.body.lr.ph.i:
; CHECK-NEXT: store i32 0, ptr [[P]], align 4
; CHECK-NEXT: [[T5_PRE:%.*]] = load ptr, ptr [[P]], align 8
; CHECK-NEXT: [[T6_PRE:%.*]] = load ptr, ptr [[T5_PRE]], align 8
; CHECK-NEXT: [[T6_PRE:%.*]] = load ptr, ptr [[T5_PRE]], align 8, !tbaa [[TBAA0]]
; CHECK-NEXT: [[T7_PRE:%.*]] = load ptr, ptr [[T6_PRE]], align 8
; CHECK-NEXT: br label [[LOOP3_LATCH]]
; CHECK: loop3.latch:
; CHECK-NEXT: [[T2_PRE_PRE23]] = phi ptr [ [[T2_PRE_PRE24]], [[LOOP3_LOOP3_LATCH_CRIT_EDGE]] ], [ [[T6_PRE]], [[FOR_BODY_LR_PH_I]] ]
; CHECK-NEXT: [[T1_PRE_PRE19]] = phi ptr [ [[T1_PRE_PRE20]], [[LOOP3_LOOP3_LATCH_CRIT_EDGE]] ], [ [[T5_PRE]], [[FOR_BODY_LR_PH_I]] ]
; CHECK-NEXT: [[T3_PRE16]] = phi ptr [ [[T3_PRE17]], [[LOOP3_LOOP3_LATCH_CRIT_EDGE]] ], [ [[T7_PRE]], [[FOR_BODY_LR_PH_I]] ]
; CHECK-NEXT: [[T2_PRE13]] = phi ptr [ [[T2_PRE14]], [[LOOP3_LOOP3_LATCH_CRIT_EDGE]] ], [ [[T6_PRE]], [[FOR_BODY_LR_PH_I]] ]
Expand All @@ -50,7 +54,7 @@ define i32 @main(i64 %x, ptr %d, ptr noalias %p) {
; CHECK: loop2.latch.loop2_crit_edge:
; CHECK-NEXT: br label [[LOOP2]]
; CHECK: loop.latch:
; CHECK-NEXT: store i32 0, ptr [[D]], align 4, !tbaa [[TBAA0:![0-9]+]]
; CHECK-NEXT: store i32 0, ptr [[D]], align 4, !tbaa [[TBAA4:![0-9]+]]
; CHECK-NEXT: br label [[LOOP]]
;
entry:
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