[all-commits] [llvm/llvm-project] 343428: MC: Detect cyclic dependency for variable symbols

[Fangrui Song via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 343428c666f9293ae260bbcf79130562b830b268
      https://github.com/llvm/llvm-project/commit/343428c666f9293ae260bbcf79130562b830b268
  Author: Fangrui Song <i at maskray.me>
  Date:   2025-05-26 (Mon, 26 May 2025)

  Changed paths:
    M llvm/include/llvm/MC/MCSymbol.h
    M llvm/lib/MC/MCExpr.cpp
    M llvm/lib/MC/MCParser/AsmParser.cpp
    M llvm/test/MC/ARM/thumb_set-diagnostics.s
    A llvm/test/MC/AsmParser/equate-cycle.s
    M llvm/test/MC/AsmParser/variables-invalid.s
    M llvm/test/MC/ELF/weakref.s
    M llvm/test/MC/Mips/set-sym-recursive.s

  Log Message:
  -----------
  MC: Detect cyclic dependency for variable symbols

We report cyclic dependency errors for variable symbols and rely on
isSymbolUsedInExpression in parseAssignmentExpression at parse time,
which does not catch all setVariableValue cases (e.g. cyclic .weakref).
Instead, add a bit to MCSymbol and check it when walking the variable
value MCExpr. When a cycle is detected when we have a final layout,
report an error and set the variable to a constant to avoid duplicate
errors.

isSymbolUsedInExpression is considered deprecated, but it is still used
by AMDGPU (#112251).



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