From 194700063ed04b56d84912f7ace1b8370af6c696 Mon Sep 17 00:00:00 2001
From: Richard Sandiford <richard.sandiford@arm.com>
Date: Sat, 11 Nov 2023 17:28:56 +0000
Subject: [PATCH 036/157] [Backport][SME] mode-switching: Fix the mode passed
 to the emit hook

Reference: https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=5afd208beaef50bcc43b556d4c41d41656b06436

optimize_mode_switching passes an entity's current mode (if known)
to the emit hook.  However, the mode that it passed ignored the
effect of the after hook.  Instead, the mode for the first emit
call in a block was taken from the incoming mode, whereas the
mode for each subsequent emit call was taken from the result
of the previous call.

The previous pass through the insns already calculated the
correct mode, so this patch records it in the seginfo structure.
(There was a 32-bit hole on 64-bit hosts, so this doesn't increase
the size of the structure for them.)

gcc/
	* mode-switching.cc (seginfo): Add a prev_mode field.
	(new_seginfo): Take and initialize the prev_mode.
	(optimize_mode_switching): Update calls accordingly.
	Use the recorded modes during the emit phase, rather than
	computing one on the fly.
---
 gcc/mode-switching.cc | 30 +++++++++++++++++-------------
 1 file changed, 17 insertions(+), 13 deletions(-)

diff --git a/gcc/mode-switching.cc b/gcc/mode-switching.cc
index 6a13951c9..584cd4f67 100644
--- a/gcc/mode-switching.cc
+++ b/gcc/mode-switching.cc
@@ -68,6 +68,7 @@ along with GCC; see the file COPYING3.  If not see
    NEXT is the next insn in the same basic block.  */
 struct seginfo
 {
+  int prev_mode;
   int mode;
   rtx_insn *insn_ptr;
   struct seginfo *next;
@@ -140,20 +141,22 @@ commit_mode_sets (struct edge_list *edge_list, int e, struct bb_info *info)
   return need_commit;
 }
 
-/* Allocate a new BBINFO structure, initialized with the MODE, INSN,
-   and REGS_LIVE parameters.
+/* Allocate a new BBINFO structure, initialized with the PREV_MODE, MODE,
+   INSN, and REGS_LIVE parameters.
    INSN may not be a NOTE_INSN_BASIC_BLOCK, unless it is an empty
    basic block; that allows us later to insert instructions in a FIFO-like
    manner.  */
 
 static struct seginfo *
-new_seginfo (int mode, rtx_insn *insn, const HARD_REG_SET &regs_live)
+new_seginfo (int prev_mode, int mode, rtx_insn *insn,
+	     const HARD_REG_SET &regs_live)
 {
   struct seginfo *ptr;
 
   gcc_assert (!NOTE_INSN_BASIC_BLOCK_P (insn)
 	      || insn == BB_END (NOTE_BASIC_BLOCK (insn)));
   ptr = XNEW (struct seginfo);
+  ptr->prev_mode = prev_mode;
   ptr->mode = mode;
   ptr->insn_ptr = insn;
   ptr->next = NULL;
@@ -589,7 +592,7 @@ optimize_mode_switching (void)
 		gcc_assert (NOTE_INSN_BASIC_BLOCK_P (ins_pos));
 		if (ins_pos != BB_END (bb))
 		  ins_pos = NEXT_INSN (ins_pos);
-		ptr = new_seginfo (no_mode, ins_pos, live_now);
+		ptr = new_seginfo (no_mode, no_mode, ins_pos, live_now);
 		add_seginfo (&tail_ptr, ptr);
 		for (i = 0; i < no_mode; i++)
 		  clear_mode_bit (transp[bb->index], j, i);
@@ -605,12 +608,12 @@ optimize_mode_switching (void)
 
 		  if (mode != no_mode && mode != last_mode)
 		    {
-		      any_set_required = true;
-		      last_mode = mode;
-		      ptr = new_seginfo (mode, insn, live_now);
+		      ptr = new_seginfo (last_mode, mode, insn, live_now);
 		      add_seginfo (&tail_ptr, ptr);
 		      for (i = 0; i < no_mode; i++)
 			clear_mode_bit (transp[bb->index], j, i);
+		      any_set_required = true;
+		      last_mode = mode;
 		    }
 
 		  if (targetm.mode_switching.after)
@@ -636,7 +639,7 @@ optimize_mode_switching (void)
 	     mark the block as nontransparent.  */
 	  if (!any_set_required)
 	    {
-	      ptr = new_seginfo (no_mode, BB_END (bb), live_now);
+	      ptr = new_seginfo (last_mode, no_mode, BB_END (bb), live_now);
 	      add_seginfo (&tail_ptr, ptr);
 	      if (last_mode != no_mode)
 		for (i = 0; i < no_mode; i++)
@@ -777,9 +780,9 @@ optimize_mode_switching (void)
       FOR_EACH_BB_FN (bb, cfun)
 	{
 	  struct seginfo *ptr, *next;
-	  int cur_mode = bb_info[j][bb->index].mode_in;
+	  struct seginfo *first = bb_info[j][bb->index].seginfo;
 
-	  for (ptr = bb_info[j][bb->index].seginfo; ptr; ptr = next)
+	  for (ptr = first; ptr; ptr = next)
 	    {
 	      next = ptr->next;
 	      if (ptr->mode != no_mode)
@@ -789,14 +792,15 @@ optimize_mode_switching (void)
 		  rtl_profile_for_bb (bb);
 		  start_sequence ();
 
+		  int cur_mode = (ptr == first && ptr->prev_mode == no_mode
+				  ? bb_info[j][bb->index].mode_in
+				  : ptr->prev_mode);
+
 		  targetm.mode_switching.emit (entity_map[j], ptr->mode,
 					       cur_mode, ptr->regs_live);
 		  mode_set = get_insns ();
 		  end_sequence ();
 
-		  /* modes kill each other inside a basic block.  */
-		  cur_mode = ptr->mode;
-
 		  /* Insert MODE_SET only if it is nonempty.  */
 		  if (mode_set != NULL_RTX)
 		    {
-- 
2.33.0