[PATCH] D97969: [SelectionDAG] Assert that operands to SelectionDAG::getNode are not DELETED_NODE to catch issues like PR49393 earlier.

[Craig Topper via Phabricator via llvm-commits]

craig.topper created this revision.
craig.topper added reviewers: spatel, RKSimon, efriedma, arsenm.
Herald added subscribers: ecnelises, hiraditya.
craig.topper requested review of this revision.
Herald added a subscriber: wdng.
Herald added a project: LLVM.

I'm not sure this would catch all such issue, but it would catch some.

The problem for PR49393 was that we were holding a reference to a node that
wasn't connect to the DAG across a function that could delete unused nodes. In
this particular case we managed to tried to use the deleted node while it was in
the deleted state before its memory got recycled.

It could also happen that we delete the node, something allocates a new node
which recycles the memory. Then  we try to use the reference we were holding and
it is now a completely different node with different valid opcode. This patch
would not catch that.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D97969

Files:
  llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp


Index: llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
===================================================================
--- llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ llvm/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -4419,6 +4419,8 @@
 
 SDValue SelectionDAG::getNode(unsigned Opcode, const SDLoc &DL, EVT VT,
                               SDValue Operand, const SDNodeFlags Flags) {
+  assert(Operand.getOpcode() != ISD::DELETED_NODE &&
+         "Operand is DELETED_NODE!");
   // Constant fold unary operations with an integer constant operand. Even
   // opaque constant will be folded, because the folding of unary operations
   // doesn't create new constants with different values. Nevertheless, the
@@ -5254,6 +5256,9 @@
 
 SDValue SelectionDAG::getNode(unsigned Opcode, const SDLoc &DL, EVT VT,
                               SDValue N1, SDValue N2, const SDNodeFlags Flags) {
+  assert(N1.getOpcode() != ISD::DELETED_NODE &&
+         N2.getOpcode() != ISD::DELETED_NODE &&
+         "Operand is DELETED_NODE!");
   ConstantSDNode *N1C = dyn_cast<ConstantSDNode>(N1);
   ConstantSDNode *N2C = dyn_cast<ConstantSDNode>(N2);
   ConstantFPSDNode *N1CFP = dyn_cast<ConstantFPSDNode>(N1);
@@ -5729,6 +5734,10 @@
 SDValue SelectionDAG::getNode(unsigned Opcode, const SDLoc &DL, EVT VT,
                               SDValue N1, SDValue N2, SDValue N3,
                               const SDNodeFlags Flags) {
+  assert(N1.getOpcode() != ISD::DELETED_NODE &&
+         N2.getOpcode() != ISD::DELETED_NODE &&
+         N3.getOpcode() != ISD::DELETED_NODE &&
+         "Operand is DELETED_NODE!");
   // Perform various simplifications.
   switch (Opcode) {
   case ISD::FMA: {
@@ -7613,6 +7622,12 @@
   default: break;
   }
 
+#ifndef NDEBUG
+  for (auto &Op : Ops)
+    assert(Op.getOpcode() != ISD::DELETED_NODE &&
+           "Operand is DELETED_NODE!");
+#endif
+
   switch (Opcode) {
   default: break;
   case ISD::BUILD_VECTOR:
@@ -7686,6 +7701,12 @@
   if (VTList.NumVTs == 1)
     return getNode(Opcode, DL, VTList.VTs[0], Ops);
 
+#ifndef NDEBUG
+  for (auto &Op : Ops)
+    assert(Op.getOpcode() != ISD::DELETED_NODE &&
+           "Operand is DELETED_NODE!");
+#endif
+
   switch (Opcode) {
   case ISD::STRICT_FP_EXTEND:
     assert(VTList.NumVTs == 2 && Ops.size() == 2 &&


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