Re: How to add a NOP instruction in each basic block for obj code that gcc generates

[Jeff <jeffhuang9999 at gmail dot com>]

> If you don't want to change the generated code other than inserting
> the nops, and you can restrict yourself to a processor which does not
> need to track addresses to avoid out-of-range branches, then you could
> approximate what you want by emitting a nop in final_scan_insn when
> you see a CODE_LABEL, after the label.  You'll need to also emit a nop
> in the first basic block in the function.  That probably won't be the
> precise set of basic blocks as the compiler sees them, but basic block
> is a somewhat nebulous concept and that may be good enough for your
> purposes, whatever they are.

Thanks, Ian.  I don't want the NOPs to affect gcc's optimization.

I've found the function final_scan_insn, which is in ./gcc/final.c.
Here is the code snippet related to CODE_LABEL:

   case CODE_LABEL:
     /* The target port might emit labels in the output function for
        some insn, e.g. sh.c output_branchy_insn.  */
     if (CODE_LABEL_NUMBER (insn) <= max_labelno)
       {
         int align = LABEL_TO_ALIGNMENT (insn);
#ifdef ASM_OUTPUT_MAX_SKIP_ALIGN
         int max_skip = LABEL_TO_MAX_SKIP (insn);
#endif

         if (align && NEXT_INSN (insn))
           {
#ifdef ASM_OUTPUT_MAX_SKIP_ALIGN
             ASM_OUTPUT_MAX_SKIP_ALIGN (file, align, max_skip);
#else
#ifdef ASM_OUTPUT_ALIGN_WITH_NOP
             ASM_OUTPUT_ALIGN_WITH_NOP (file, align);
#else
             ASM_OUTPUT_ALIGN (file, align);
#endif
#endif
           }
       }

Which function should I use in order to emit a nop?

Thanks,
Jeff