[llvm] [SelectionDAG] Salvage debug info for non-constant ADDs (PR #68981)

[Shengchen Kan via llvm-commits]

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@@ -10791,27 +10795,46 @@ void SelectionDAG::salvageDebugInfo(SDNode &N) {
         auto *DIExpr = DV->getExpression();
         auto NewLocOps = DV->copyLocationOps();
         bool Changed = false;
-        for (size_t i = 0; i < NewLocOps.size(); ++i) {
+        size_t OrigLocOpsSize = NewLocOps.size();
+        for (size_t i = 0; i < OrigLocOpsSize; ++i) {
           // We're not given a ResNo to compare against because the whole
           // node is going away. We know that any ISD::ADD only has one
           // result, so we can assume any node match is using the result.
           if (NewLocOps[i].getKind() != SDDbgOperand::SDNODE ||
               NewLocOps[i].getSDNode() != &N)
             continue;
           NewLocOps[i] = SDDbgOperand::fromNode(N0.getNode(), N0.getResNo());
-          SmallVector<uint64_t, 3> ExprOps;
-          DIExpression::appendOffset(ExprOps, Offset);
-          DIExpr = DIExpression::appendOpsToArg(DIExpr, ExprOps, i, true);
+          if (RHSConstant) {
+            SmallVector<uint64_t, 3> ExprOps;
+            DIExpression::appendOffset(ExprOps, Offset);
+            DIExpr = DIExpression::appendOpsToArg(DIExpr, ExprOps, i, true);
+          } else {
+            // Convert to a variadic expression (if not already).
+            // convertToVariadicExpression() returns a const pointer, so we use
+            // a temporary const variable here.
+            const auto *TmpDIExpr =
+                DIExpression::convertToVariadicExpression(DIExpr);
+            SmallVector<uint64_t, 3> ExprOps;
+            ExprOps.push_back(dwarf::DW_OP_LLVM_arg);
+            ExprOps.push_back(NewLocOps.size());
+            ExprOps.push_back(dwarf::DW_OP_plus);
+            SDDbgOperand RHS =
+                SDDbgOperand::fromNode(N1.getNode(), N1.getResNo());
+            NewLocOps.push_back(RHS);
+            DIExpr = DIExpression::appendOpsToArg(TmpDIExpr, ExprOps, i, true);
+          }
           Changed = true;
         }
         (void)Changed;
         assert(Changed && "Salvage target doesn't use N");
 
+        bool IsVariadic =
+            DV->isVariadic() || OrigLocOpsSize != NewLocOps.size();
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KanRobert wrote:

https://github.com/llvm/llvm-project/issues/72630

https://github.com/llvm/llvm-project/pull/68981