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[NFC][SROA][DebugInfo] Reuse existing dbg_assigns where possible #163938

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Oct 17, 2025
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[NFC][SROA][DebugInfo] Reuse existing dbg_assigns where possible #163938

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847ae03
[SROA] Reuse existing dbg_assigns where possible
OCHyams Oct 16, 2025
3bdaa79
clang-format
OCHyams Oct 17, 2025
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34 changes: 26 additions & 8 deletions llvm/lib/Transforms/Scalar/SROA.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -340,6 +340,12 @@ static void migrateDebugInfo(AllocaInst *OldAlloca, bool IsSplit,
uint64_t SliceSizeInBits, Instruction *OldInst,
Instruction *Inst, Value *Dest, Value *Value,
const DataLayout &DL) {
// If we want allocas to be migrated using this helper then we need to ensure
// that the BaseFragments map code still works. A simple solution would be
// to choose to always clone alloca dbg_assigns (rather than sometimes
// "stealing" them).
assert(!isa<AllocaInst>(Inst) && "Unexpected alloca");

auto DVRAssignMarkerRange = at::getDVRAssignmentMarkers(OldInst);
// Nothing to do if OldInst has no linked dbg.assign intrinsics.
if (DVRAssignMarkerRange.empty())
Expand Down Expand Up @@ -425,11 +431,22 @@ static void migrateDebugInfo(AllocaInst *OldAlloca, bool IsSplit,
Inst->setMetadata(LLVMContext::MD_DIAssignID, NewID);
}

::Value *NewValue = Value ? Value : DbgAssign->getValue();
DbgVariableRecord *NewAssign = cast<DbgVariableRecord>(cast<DbgRecord *>(
DIB.insertDbgAssign(Inst, NewValue, DbgAssign->getVariable(), Expr,
Dest, DIExpression::get(Expr->getContext(), {}),
DbgAssign->getDebugLoc())));
DbgVariableRecord *NewAssign;
if (IsSplit) {
::Value *NewValue = Value ? Value : DbgAssign->getValue();
NewAssign = cast<DbgVariableRecord>(cast<DbgRecord *>(
DIB.insertDbgAssign(Inst, NewValue, DbgAssign->getVariable(), Expr,
Dest, DIExpression::get(Expr->getContext(), {}),
DbgAssign->getDebugLoc())));
} else {
// The store is not split, simply steal the existing dbg_assign.
NewAssign = DbgAssign;
NewAssign->setAssignId(NewID); // FIXME: Can we avoid generating new IDs?
NewAssign->setAddress(Dest);
if (Value)
NewAssign->replaceVariableLocationOp(0u, Value);
assert(Expr == NewAssign->getExpression());
}

// If we've updated the value but the original dbg.assign has an arglist
// then kill it now - we can't use the requested new value.
Expand Down Expand Up @@ -460,9 +477,10 @@ static void migrateDebugInfo(AllocaInst *OldAlloca, bool IsSplit,
// noted as slightly offset (in code) from the store. In practice this
// should have little effect on the debugging experience due to the fact
// that all the split stores should get the same line number.
NewAssign->moveBefore(DbgAssign->getIterator());

NewAssign->setDebugLoc(DbgAssign->getDebugLoc());
if (NewAssign != DbgAssign) {
NewAssign->moveBefore(DbgAssign->getIterator());
NewAssign->setDebugLoc(DbgAssign->getDebugLoc());
}
LLVM_DEBUG(dbgs() << "Created new assign: " << *NewAssign << "\n");
};

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