[llvm] [X86Backend] Use GetExternalSymbolSymbol for MO_ExternalSymbol. (PR #133352)

[weiwei chen via llvm-commits]

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@@ -192,8 +192,15 @@ MCSymbol *X86MCInstLower::GetSymbolFromOperand(const MachineOperand &MO) const {
   }
 
   Name += Suffix;
-  if (!Sym)
-    Sym = Ctx.getOrCreateSymbol(Name);
+  if (!Sym) {
+    // If new MCSymbol needs to be created for
+    // MachineOperand::MO_ExternalSymbol, create it as a symbol
+    // in AsmPrinter's OutContext.
+    if (MO.isSymbol())
+      Sym = AsmPrinter.OutContext.getOrCreateSymbol(Name);
+    else
+      Sym = Ctx.getOrCreateSymbol(Name);
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weiweichen wrote:

> said, more generally, if you want everything to work reliably, you'll probably need to completely eliminate the MCContext reference from MachineFunction. Otherwise, you'll continue to run into issues where the MCSymbol is from the wrong context. Maybe doable, but involves a significant amount of refactoring to avoid constructing MCSymbols early... and I'm not sure if there are any other weird interactions here.

Interesting idea, but I do need to think more about what does this entails, and as you said, it will probably be a significant amount of refactoring, so maybe as follow-ups with more concrete considerations on a larger scale refactoring? 

(Also very selfishly speaking, this PR will help significantly with our MCLinker to function correctly, otherwise, half of tests are failing now 😢, so would be great to get something in first so that we can keep upgrading weekly 🙏 . )

https://github.com/llvm/llvm-project/pull/133352