[PATCH] D55227: [DebugInfo] Don't drop dbg.value's of nullptr

[David Stenberg via Phabricator via llvm-commits]

dstenb added inline comments.


================
Comment at: lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp:5305
+    if (isa<ConstantInt>(V) || isa<ConstantFP>(V) || isa<UndefValue>(V) ||
+        isa<ConstantPointerNull>(V)) {
       SDV = DAG.getConstantDbgValue(Variable, Expression, V, dl, SDNodeOrder);
----------------
vsk wrote:
> I'm curious what happens if V is-a Constant, but not one of these constants (e.g ConstantAggregate). It seems unlikely that V would always be in NodeMap in that case.
If it is not something that is in NodeMap here, nor resolved later via DanglingDebugInfoMap, then nothing will be emitted, so the preceding dbg value can live longer than expected. There is the following TODO for this:

```
    // TODO: When we get here we will either drop the dbg.value completely, or
    // we try to move it forward by letting it dangle for awhile. So we should
    // probably add an extra DbgValue to the DAG here, with a reference to
    // "noreg", to indicate that we have lost the debug location for the
    // variable.

```


Repository:
  rL LLVM

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D55227/new/

https://reviews.llvm.org/D55227