[llvm] [DebugInfo] Lower DW_OP_LLVM_implicit_pointer to DWARF (PR #186763)

[Shivam Kunwar via llvm-commits]

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@@ -776,8 +776,125 @@ DIE *DwarfCompileUnit::constructVariableDIE(DbgVariable &DV, bool Abstract) {
   return VariableDie;
 }
 
+static const DIType *resolveTypeQualifiers(const DIType *Ty) {
+  while (const auto *DT = dyn_cast_or_null<DIDerivedType>(Ty)) {
+    switch (DT->getTag()) {
+    case dwarf::DW_TAG_typedef:
+    case dwarf::DW_TAG_const_type:
+    case dwarf::DW_TAG_volatile_type:
+    case dwarf::DW_TAG_restrict_type:
+    case dwarf::DW_TAG_atomic_type:
+      Ty = DT->getBaseType();
+      continue;
+    default:
+      return Ty;
+    }
+  }
+  return Ty;
+}
+
+bool DwarfCompileUnit::emitImplicitPointerLocation(const Loc::Single &Single,
+                                                   const DbgVariable &DV,
+                                                   DIE &VariableDie) {
+  const auto *Expr = Single.getExpr();
+  if (!Expr)
+    return false;
+
+  // Only handle the simple case where DW_OP_LLVM_implicit_pointer is the
+  // sole operation (or followed only by DW_OP_LLVM_fragment).
+  //
+  // Multi-level implicit pointers (e.g., int **pp where both levels are
+  // optimized away) would require stacking multiple implicit_pointer ops
+  // in one expression and unwinding them into a chain of artificial DIEs.
+  // This is left for future work.
+  //
+  // Location list support (Loc::Multi) is not yet handled.
+  auto ExprOps = Expr->expr_ops();
+  auto FirstOp = ExprOps.begin();
+  if (FirstOp == ExprOps.end() ||
+      FirstOp->getOp() != dwarf::DW_OP_LLVM_implicit_pointer)
+    return false;
+
+  if (DD->getDwarfVersion() < 4)
+    return false;
+
+  const auto &DVal = Single.getValueLoc();
+  if (DVal.isVariadic())
+    return false;
+
+  const auto &Entry = DVal.getLocEntries()[0];
----------------
phyBrackets wrote:

Yes, non-variadic values always have exactly one entry. The isVariadic() check above guarantees this. Added an assert to make it explicit.

https://github.com/llvm/llvm-project/pull/186763