[llvm] [SROA] Fix incorrect offsets for structured binding variables (PR #69007)

[Jeremy Morse via llvm-commits]

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@@ -4813,54 +4813,43 @@ bool SROAPass::splitAlloca(AllocaInst &AI, AllocaSlices &AS) {
   for (auto *DbgAssign : at::getAssignmentMarkers(&AI))
     DbgVariables.push_back(DbgAssign);
   for (DbgVariableIntrinsic *DbgVariable : DbgVariables) {
-    auto *Expr = DbgVariable->getExpression();
     DIBuilder DIB(*AI.getModule(), /*AllowUnresolved*/ false);
-    uint64_t AllocaSize =
-        DL.getTypeSizeInBits(AI.getAllocatedType()).getFixedValue();
-    for (auto Fragment : Fragments) {
-      // Create a fragment expression describing the new partition or reuse AI's
-      // expression if there is only one partition.
-      auto *FragmentExpr = Expr;
-      if (Fragment.Size < AllocaSize || Expr->isFragment()) {
-        // If this alloca is already a scalar replacement of a larger aggregate,
-        // Fragment.Offset describes the offset inside the scalar.
-        auto ExprFragment = Expr->getFragmentInfo();
-        uint64_t Offset = ExprFragment ? ExprFragment->OffsetInBits : 0;
-        uint64_t Start = Offset + Fragment.Offset;
-        uint64_t Size = Fragment.Size;
-        if (ExprFragment) {
-          uint64_t AbsEnd =
-              ExprFragment->OffsetInBits + ExprFragment->SizeInBits;
-          if (Start >= AbsEnd) {
-            // No need to describe a SROAed padding.
-            continue;
-          }
-          Size = std::min(Size, AbsEnd - Start);
-        }
-        // The new, smaller fragment is stenciled out from the old fragment.
-        if (auto OrigFragment = FragmentExpr->getFragmentInfo()) {
-          assert(Start >= OrigFragment->OffsetInBits &&
-                 "new fragment is outside of original fragment");
-          Start -= OrigFragment->OffsetInBits;
-        }
 
-        // The alloca may be larger than the variable.
-        auto VarSize = DbgVariable->getVariable()->getSizeInBits();
-        if (VarSize) {
-          if (Size > *VarSize)
-            Size = *VarSize;
-          if (Size == 0 || Start + Size > *VarSize)
-            continue;
-        }
-
-        // Avoid creating a fragment expression that covers the entire variable.
-        if (!VarSize || *VarSize != Size) {
-          if (auto E =
-                  DIExpression::createFragmentExpression(Expr, Start, Size))
-            FragmentExpr = *E;
-          else
-            continue;
-        }
+    for (auto Fragment : Fragments) {
+      uint64_t OffestFromNewAllocaInBits;
+      std::optional<DIExpression::FragmentInfo> NewDbgFragment;
+
+      // Drop debug info for this variable fragment if we can't compute an
+      // intersect between it and the alloca slice.
+      if (!at::calculateFragmentIntersect(
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jmorse wrote:

Worth promoting this function out of the at:: namespace if it's being generalised so far?

https://github.com/llvm/llvm-project/pull/69007