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Keep track of the FUNCTION_BEG note

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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.

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.
This commit is contained in:
Richard Sandiford 2024-01-12 12:38:00 +00:00
parent 81d309168b
commit 0d74ff2d7e
2 changed files with 5 additions and 1 deletions
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4
gcc/emit-rtl.h
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@ -141,6 +141,9 @@ struct GTY(()) rtl_data {
If stack grows up, this is the address for the next slot. */
poly_int64 x_frame_offset;
/* The function's FUNCTION_BEG note. */
rtx_insn *x_function_beg_insn;
/* Insn after which register parms and SAVE_EXPRs are born, if nonopt. */
rtx_insn *x_parm_birth_insn;
@ -323,6 +326,7 @@ struct GTY(()) rtl_data {
#define return_label (crtl->x_return_label)
#define naked_return_label (crtl->x_naked_return_label)
#define stack_slot_list (crtl->x_stack_slot_list)
#define function_beg_insn (crtl->x_function_beg_insn)
#define parm_birth_insn (crtl->x_parm_birth_insn)
#define frame_offset (crtl->x_frame_offset)
#define stack_check_probe_note (crtl->x_stack_check_probe_note)

2
gcc/function.cc
View file

@ -5202,7 +5202,7 @@ expand_function_start (tree subr)
gcc_assert (NOTE_P (get_last_insn ()));
parm_birth_insn = get_last_insn ();
function_beg_insn = parm_birth_insn = get_last_insn ();
/* If the function receives a non-local goto, then store the
bits we need to restore the frame pointer. */