Revert "[SelectionDAG] Salvage debug info for non-constant ADDs (#68981)"

This reverts commit 3ab03ad.

Reverted due to failing expensive-checks buildbots, e.g.
https://lab.llvm.org/buildbot/#/builders/16/builds/56317. Will
investigate that.

Author: dstenb

llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp

@@ -27,7 +27,6 @@
 #include "llvm/Analysis/MemoryLocation.h"
 #include "llvm/Analysis/ValueTracking.h"
 #include "llvm/Analysis/VectorUtils.h"
-#include "llvm/BinaryFormat/Dwarf.h"
 #include "llvm/CodeGen/Analysis.h"
 #include "llvm/CodeGen/FunctionLoweringInfo.h"
 #include "llvm/CodeGen/ISDOpcodes.h"
@@ -10844,11 +10843,8 @@ void SelectionDAG::salvageDebugInfo(SDNode &N) {
     case ISD::ADD: {
       SDValue N0 = N.getOperand(0);
       SDValue N1 = N.getOperand(1);
-      if (!isa<ConstantSDNode>(N0)) {
-        bool RHSConstant = isa<ConstantSDNode>(N1);
-        uint64_t Offset;
-        if (RHSConstant)
-          Offset = N.getConstantOperandVal(1);
+      if (!isa<ConstantSDNode>(N0) && isa<ConstantSDNode>(N1)) {
+        uint64_t Offset = N.getConstantOperandVal(1);
 
         // Rewrite an ADD constant node into a DIExpression. Since we are
         // performing arithmetic to compute the variable's *value* in the
@@ -10857,46 +10853,27 @@ void SelectionDAG::salvageDebugInfo(SDNode &N) {
         auto *DIExpr = DV->getExpression();
         auto NewLocOps = DV->copyLocationOps();
         bool Changed = false;
-        size_t OrigLocOpsSize = NewLocOps.size();
-        for (size_t i = 0; i < OrigLocOpsSize; ++i) {
+        for (size_t i = 0; i < NewLocOps.size(); ++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());
-          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);
-          }
+          SmallVector<uint64_t, 3> ExprOps;
+          DIExpression::appendOffset(ExprOps, Offset);
+          DIExpr = DIExpression::appendOpsToArg(DIExpr, ExprOps, i, true);
           Changed = true;
         }
         (void)Changed;
         assert(Changed && "Salvage target doesn't use N");
 
-        bool IsVariadic =
-            DV->isVariadic() || OrigLocOpsSize != NewLocOps.size();
-
         auto AdditionalDependencies = DV->getAdditionalDependencies();
-        SDDbgValue *Clone = getDbgValueList(
-            DV->getVariable(), DIExpr, NewLocOps, AdditionalDependencies,
-            DV->isIndirect(), DV->getDebugLoc(), DV->getOrder(), IsVariadic);
+        SDDbgValue *Clone = getDbgValueList(DV->getVariable(), DIExpr,
+                                            NewLocOps, AdditionalDependencies,
+                                            DV->isIndirect(), DV->getDebugLoc(),
+                                            DV->getOrder(), DV->isVariadic());
         ClonedDVs.push_back(Clone);
         DV->setIsInvalidated();
         DV->setIsEmitted();