[llvm] [MC][AsmPrinter] Introduce llvm_reg_offset pseudo cfi instruction. (PR #125104)

[Michael Maitland via llvm-commits]

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@@ -634,6 +649,22 @@ class MCCFIInstruction {
     return MCCFIInstruction(OpRegister, L, Register1, Register2, Loc);
   }
 
+  /// This is a "pseudo CFI" instruction which generates the escape expression
+  /// deref(FrameReg + Offset) for the register Reg.
+  static void createRegOffsetExpression(unsigned Reg, unsigned FrameReg,
+                                        int64_t Offset,
+                                        SmallString<64> &CFAExpr);
+  static MCCFIInstruction createLLVMRegOffset(MCSymbol *L, unsigned Reg,
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michaelmaitland wrote:

This function needs a docstring like the other `createXXX` functions in this file. This helps us document the form of this instruction and how it works.

https://github.com/llvm/llvm-project/pull/125104