Implement salavageDebugInfo functionality for SelectionDAG.

Similar to how llvm::salvagDebugInfo hooks into InstCombine, this adds
a hook that can be invoked before an SDNode that is associated with an
SDDbgValue is erased to capture the effect of the deleted node in a
DIExpression.

The motivating example is an SDDebugValue attached to an ADD operation
that gets folded into a LOAD+OFFSET operation.

rdar://problem/32121503

llvm-svn: 316525

2 files changed, 35 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index f712862f184..dd5e1e5a3ee 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -6978,6 +6978,40 @@ SDDbgValue *SelectionDAG::getFrameIndexDbgValue(DIVariable *Var,
   return new (DbgInfo->getAlloc()) SDDbgValue(Var, Expr, FI, DL, O);
 }
 
+void SelectionDAG::salvageDebugInfo(SDNode &N) {
+  if (!N.getHasDebugValue())
+    return;
+  for (auto DV : GetDbgValues(&N)) {
+    if (DV->isInvalidated())
+      continue;
+    switch (N.getOpcode()) {
+    default:
+      break;
+    case ISD::ADD:
+      SDValue N0 = N.getOperand(0);
+      SDValue N1 = N.getOperand(1);
+      if (!isConstantIntBuildVectorOrConstantInt(N0) &&
+          isConstantIntBuildVectorOrConstantInt(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
+        // DIExpression, we need to mark the expression with a
+        // DW_OP_stack_value.
+        auto *DIExpr = DV->getExpression();
+        DIExpr = DIExpression::prepend(DIExpr, DIExpression::NoDeref, Offset,
+                                       DIExpression::WithStackValue);
+        SDDbgValue *Clone =
+            getDbgValue(DV->getVariable(), DIExpr, N0.getNode(), N0.getResNo(),
+                        DV->isIndirect(), DV->getDebugLoc(), DV->getOrder());
+        DV->setIsInvalidated();
+        AddDbgValue(Clone, N0.getNode(), false);
+        DEBUG(dbgs() << "SALVAGE: Rewriting"; N0.getNode()->dumprFull(this);
+              dbgs() << " into " << *DIExpr << '\n');
+      }
+    }
+  }
+}
+
 namespace {
 
 /// RAUWUpdateListener - Helper for ReplaceAllUsesWith - When the node
diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
index 5311ef437e9..4c4d196427e 100644
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGISel.cpp
@@ -3550,6 +3550,7 @@ void SelectionDAGISel::SelectCodeCommon(SDNode *NodeToMatch,
                "NodeToMatch was removed partway through selection");
         SelectionDAG::DAGNodeDeletedListener NDL(*CurDAG, [&](SDNode *N,
                                                               SDNode *E) {
+          CurDAG->salvageDebugInfo(*N);
           auto &Chain = ChainNodesMatched;
           assert((!E || !is_contained(Chain, N)) &&
                  "Chain node replaced during MorphNode");