[PATCH] D71443: [MC][PowerPC] Fix a crash when redefining a symbol after .set

[Fangrui Song via Phabricator via llvm-commits]

MaskRay added a comment.

In D71443#1973732 <https://reviews.llvm.org/D71443#1973732>, @nemanjai wrote:

> @MaskRay @luporl Is it possible for `Sym` to be `null` here? Do we need a `nullptr` check? I ask because we seem to have a crash here reported in https://bugs.llvm.org/show_bug.cgi?id=45366 that we cannot reproduce. But I wonder if perhaps this might be the issue.
>
> I have asked the OP of the PR to try the patch that adds the null check, but I was hoping to get your opinion on this as well.


In a -DLLVM_ENABLE_ASSERTIONS=on build, `Sym` can't be `nullptr`. Might to good to ask the OP of https://bugs.llvm.org/show_bug.cgi?id=45366 whether this can be reproduced

  void emitAssignment(MCSymbol *S, const MCExpr *Value) override {
    auto *Symbol = cast<MCSymbolELF>(S); //////////// asserted to be non-null
  
    // When encoding an assignment to set symbol A to symbol B, also copy
    // the st_other bits encoding the local entry point offset.
    if (copyLocalEntry(Symbol, Value))
      UpdateOther.insert(Symbol); ///////// only way an element is inserted into UpdateOther
    else
      UpdateOther.erase(Symbol);
  }

Here is the only caller of `llvm::MCTargetStreamer::emitAssignment`

  // https://github.com/llvm/llvm-project/blob/master/llvm/lib/MC/MCStreamer.cpp#L966
  void MCStreamer::emitAssignment(MCSymbol *Symbol, const MCExpr *Value) {
    visitUsedExpr(*Value);
    Symbol->setVariableValue(Value);
  
    MCTargetStreamer *TS = getTargetStreamer();
    if (TS)
      TS->emitAssignment(Symbol, Value);  //////////// Symbol can't be nullptr
  }


Repository:
  rG LLVM Github Monorepo

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https://reviews.llvm.org/D71443