Re: [PATCH] Keep track of the FUNCTION_BEG note

[Jeff Law <jeffreyalaw@gmail.com>]

On 1/5/24 09:28, Richard Sandiford wrote:
> function.cc emits a NOTE_FUNCTION_BEG after all arguments have
> been copied to pseudos.  It then records this note in parm_birth_insn.
> Various other pieces of code use this insn as a convenient place to
> insert things at the start of the function.
> 
> However, cfgexpand later changes parm_birth_insn as follows:
> 
>    /* If we emitted any instructions for setting up the variables,
>       emit them before the FUNCTION_START note.  */
>    if (var_seq)
>      {
>        emit_insn_before (var_seq, parm_birth_insn);
> 
>        /* In expand_function_end we'll insert the alloca save/restore
> 	 before parm_birth_insn.  We've just insertted an alloca call.
> 	 Adjust the pointer to match.  */
>        parm_birth_insn = var_seq;
>      }
> 
> But the FUNCTION_BEG note is still useful for things that aren't
> sensitive to stack allocation, and it has the advantage that
> (unlike the var_seq above) it is never deleted or combined.
> This patch adds a separate variable to track it.
> 
> Tested on aarch64-linux-gnu, where it's needed for fixing PR113196.
> OK to install?
> 
> Richard
> 
> 
> gcc/
> 	* emit-rtl.h (rtl_data::x_function_beg_note): New member variable.
> 	(function_beg_insn): New macro.
> 	* function.cc (expand_function_start): Initialize function_beg_insn.
OK
jeff