[Assignment Tracking] Trim assignments for untagged out of bounds stores (#66095)

Fixes #65004 by trimming assignments from out of bounds stores (out of bounds
of either the base variable or the backing alloca). If there's no overlap at
all or the out of bounds access starts at a negative offset from the alloca,
the assignment is simply skipped.

1 files changed, 17 insertions, 14 deletions

diff --git a/llvm/lib/CodeGen/AssignmentTrackingAnalysis.cpp b/llvm/lib/CodeGen/AssignmentTrackingAnalysis.cpp
index 5ef850d..5b569755 100644
--- a/llvm/lib/CodeGen/AssignmentTrackingAnalysis.cpp
+++ b/llvm/lib/CodeGen/AssignmentTrackingAnalysis.cpp
@@ -1979,20 +1979,23 @@ static AssignmentTrackingLowering::OverlapMap buildOverlapMapAndRecordDeclares(
                      I, Fn.getParent()->getDataLayout())) {
         // Find markers linked to this alloca.
         for (DbgAssignIntrinsic *DAI : at::getAssignmentMarkers(Info->Base)) {
-          // Discard the fragment if it covers the entire variable.
-          std::optional<DIExpression::FragmentInfo> FragInfo =
-              [&Info, DAI]() -> std::optional<DIExpression::FragmentInfo> {
-            DIExpression::FragmentInfo F;
-            F.OffsetInBits = Info->OffsetInBits;
-            F.SizeInBits = Info->SizeInBits;
-            if (auto ExistingFrag = DAI->getExpression()->getFragmentInfo())
-              F.OffsetInBits += ExistingFrag->OffsetInBits;
-            if (auto Sz = DAI->getVariable()->getSizeInBits()) {
-              if (F.OffsetInBits == 0 && F.SizeInBits == *Sz)
-                return std::nullopt;
-            }
-            return F;
-          }();
+          std::optional<DIExpression::FragmentInfo> FragInfo;
+
+          // Skip this assignment if the affected bits are outside of the
+          // variable fragment.
+          if (!at::calculateFragmentIntersect(
+                  I.getModule()->getDataLayout(), Info->Base,
+                  Info->OffsetInBits, Info->SizeInBits, DAI, FragInfo) ||
+              (FragInfo && FragInfo->SizeInBits == 0))
+            continue;
+
+          // FragInfo from calculateFragmentIntersect is nullopt if the
+          // resultant fragment matches DAI's fragment or entire variable - in
+          // which case copy the fragment info from DAI. If FragInfo is still
+          // nullopt after the copy it means "no fragment info" instead, which
+          // is how it is usually interpreted.
+          if (!FragInfo)
+            FragInfo = DAI->getExpression()->getFragmentInfo();
 
           DebugVariable DV = DebugVariable(DAI->getVariable(), FragInfo,
                                            DAI->getDebugLoc().getInlinedAt());