[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:

> If preventing that is the goal, why not change X86MCInstLower::X86MCInstLower instead? Just change `Ctx(mf.getContext())` to `Ctx(asmprinter.OutContext)`.

Hmmm, this probably won't work (I mean it will work for MO_ExternalSymbol to get a unique MCSymbol, but) because we do still need `mf.getContext()` to do most of the codegen here for this function pass to run on the corresponding `MachineFunction`. `Ctx` has to be `mf.getContext()` as most of  the codegen for this MachineFunction is in this MCContext. AsmPrinter's OutContext is just for the output here.

Yeah, for most cases, `AsmPrinter.OutContext` is the same as `mf.getContext` because there is just one `MCContext` in the whole pipeline. I'm not sure what is the motivation for other backends to also use `AsmPrinter.OutContext` for the same case here, but the change does make them look more consistent with each other 😀 




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