[PATCH] D153008: [RISCV] Allow slash-star comments in instruction operands

[Abel Bernabeu via Phabricator via cfe-commits]

abel-bernabeu updated this revision to Diff 531741.
abel-bernabeu added a comment.

  [RISCV] Allow slash-star comments in instruction operands
  
  It has been reported by one of Esperanto's customers that slash-start
  comments ("/*") within inline assembly were only allowed before the
  first instruction operand or at the end of the lines. Those comments
  were, however, not allowed when interleaved within the operands.
  
  An example follows:
  
  ```
  unsigned long int dst;
  __asm__ __volatile__(
    "li /* this was fine */ %[dst], /* this was NOT fine */ 0x1234\n"
    "add zero, %[dst], %[dst]\n"
    : [ dst ] "=r"(dst)
    :
    :);
  ```
  
  A code review of the top level parser (AsmParser class) showed that
  when comments were placed before the instruction operand or at end of
  a line, then they were gracefully handled irrespective of the backend.
  When the comments were interleaved within the instruction operands it
  was the backend's responsibility to handle the comments.
  
  RISC-V's backend did not handle the comments in any way.
  
  Beyond the obvious solution of explicitly handling the comments within
  the RISC-V backend, another, easier to maintain solution was suggested
  by Sergei Barannikov in a Discourse discussion thread:
  
  https://discourse.llvm.org/t/interleaving-several-c-style-comments-in-the-same-inline-assembly-line/71353/8
  
  In summary, all backends, including the RISC-V's, should switch
  from getLexer().Lex() to getParser().Lex() in their ParseInstruction
  implementation.
  
  The getLexer().Lex() approach relies on the user to explicitly handle
  the comments, whereas the suggested getParser().Lex() alternive already
  handles the comments in the same way as done for non-target-specific
  assembly directives.
  
  Here we just do the RISC-V work. Other backends should also do their own
  review.
  
  In addition to Sergei Barannikov, I would also like to thank David Spikett
  from Arm's community for pointing out where to start looking within the
  LLVM code base, and also the patch reviewers.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D153008/new/

https://reviews.llvm.org/D153008

Files:
  clang/test/CodeGen/RISCV/riscv-inline-asm-gcc-commenting.c
  llvm/lib/Target/RISCV/AsmParser/RISCVAsmParser.cpp

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