[llvm] [AMDGPU][AsmParser] Simplify getting source locations of operands. (PR #158323)

[Ivan Kosarev via llvm-commits]

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@@ -228,6 +213,9 @@ class AMDGPUOperand : public MCParsedAsmOperand {
     const MCExpr *Expr;
   };
 
+  // The index of the associated MCInst operand.
+  mutable int MCOpIdx = -1;
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kosarev wrote:

Would take all the AddImm*() / AddReg*() members to lose their const qualifiers. Alternatively, since AMDGPUOperands store a reference to the AsmParser, we could store the mapping there, which looks more complicated than necessary and then again requires dealing with the const-ness of that reference. Wasn't able to convince myself any of the options are worth it.

Note that the removed `ImmKindTy Kind` field was also declared mutable, so the patch doesn't make it worse.

https://github.com/llvm/llvm-project/pull/158323