csa, postreload: Improve csa after recent cselib changes [PR94516]

This patch addresses a missed optimization caused by the cselib changes.
Already in the past postreload could replace sp = sp + const_int with
sp = regxy if regxy already has the right value, but with the cselib
changes it happens several times more often.  It can result in smaller
code, so it seems undesirable to prevent such optimizations, but
unfortunately it can get into the way of stack adjustment coalescing,
where e.g. if we used to have sp = sp + 32; sp = sp - 8;, previously
we'd turn that into sp = sp + 24;, but now postreload optimizes
into sp = r12; sp = sp - 8; and csa gives up.

The patch just adds a REG_EQUAL note when changing sp = sp + const into
sp = reg, where we remember it was actually a stack adjustment by certain
constant, and the combine-stack-adj changes than make use of those REG_EQUAL
notes, together with LR tracking (csa did enable the note problem, just
didn't simulate each insn) so that we can add the needed clobbers etc.
(taken from the other stack adjustment insn).

2020-05-05  Jakub Jelinek  <jakub@redhat.com>

	PR rtl-optimization/94516
	* postreload.c (reload_cse_simplify): When replacing sp = sp + const
	with sp = reg, add REG_EQUAL note with sp + const.
	* combine-stack-adj.c (try_apply_stack_adjustment): Change return
	type from int to bool.  Add LIVE and OTHER_INSN arguments.  Undo
	postreload sp = sp + const to sp = reg optimization if needed and
	possible.
	(combine_stack_adjustments_for_block): Add LIVE argument.  Handle
	reg = sp insn with sp + const REG_EQUAL note.  Adjust
	try_apply_stack_adjustment caller, call
	df_simulate_initialize_forwards and df_simulate_one_insn_forwards.
	(combine_stack_adjustments): Allocate and free LIVE bitmap,
	adjust combine_stack_adjustments_for_block caller.

1 files changed, 119 insertions, 17 deletions

diff --git a/gcc/combine-stack-adj.c b/gcc/combine-stack-adj.c
index 073b7f0..281166b 100644
--- a/gcc/combine-stack-adj.c
+++ b/gcc/combine-stack-adj.c
@@ -70,9 +70,10 @@ static rtx single_set_for_csa (rtx_insn *);
 static void free_csa_reflist (struct csa_reflist *);
 static struct csa_reflist *record_one_stack_ref (rtx_insn *, rtx *,
 						 struct csa_reflist *);
-static int try_apply_stack_adjustment (rtx_insn *, struct csa_reflist *,
-				       HOST_WIDE_INT, HOST_WIDE_INT);
-static void combine_stack_adjustments_for_block (basic_block);
+static bool try_apply_stack_adjustment (rtx_insn *, struct csa_reflist *,
+					HOST_WIDE_INT, HOST_WIDE_INT,
+					bitmap, rtx_insn *);
+static void combine_stack_adjustments_for_block (basic_block, bitmap);
 
 
 /* Main entry point for stack adjustment combination.  */
@@ -81,9 +82,12 @@ static void
 combine_stack_adjustments (void)
 {
   basic_block bb;
+  bitmap live = BITMAP_ALLOC (&reg_obstack);
 
   FOR_EACH_BB_FN (bb, cfun)
-    combine_stack_adjustments_for_block (bb);
+    combine_stack_adjustments_for_block (bb, live);
+
+  BITMAP_FREE (live);
 }
 
 /* Recognize a MEM of the form (sp) or (plus sp const).  */
@@ -219,18 +223,60 @@ no_unhandled_cfa (rtx_insn *insn)
    as each of the memories and stack references in REFLIST.  Return true
    on success.  */
 
-static int
+static bool
 try_apply_stack_adjustment (rtx_insn *insn, struct csa_reflist *reflist,
-			    HOST_WIDE_INT new_adjust, HOST_WIDE_INT delta)
+			    HOST_WIDE_INT new_adjust, HOST_WIDE_INT delta,
+			    bitmap live, rtx_insn *other_insn)
 {
   struct csa_reflist *ml;
   rtx set;
+  bool remove_equal = false;
 
   set = single_set_for_csa (insn);
   if (MEM_P (SET_DEST (set)))
     validate_change (insn, &SET_DEST (set),
 		     replace_equiv_address (SET_DEST (set), stack_pointer_rtx),
 		     1);
+  else if (REG_P (SET_SRC (set)))
+    {
+      if (other_insn == NULL_RTX || live == NULL)
+	return false;
+      rtx other_set = single_set_for_csa (other_insn);
+      if (SET_DEST (other_set) != stack_pointer_rtx
+	  || GET_CODE (SET_SRC (other_set)) != PLUS
+	  || XEXP (SET_SRC (other_set), 0) != stack_pointer_rtx
+	  || !CONST_INT_P (XEXP (SET_SRC (other_set), 1)))
+	return false;
+      if (PATTERN (other_insn) != other_set)
+	{
+	  if (GET_CODE (PATTERN (other_insn)) != PARALLEL)
+	    return false;
+	  int i;
+	  rtx p = PATTERN (other_insn);
+	  for (i = 0; i < XVECLEN (p, 0); ++i)
+	    {
+	      rtx this_rtx = XVECEXP (p, 0, i);
+	      if (this_rtx == other_set)
+		continue;
+	      if (GET_CODE (this_rtx) != CLOBBER)
+		return false;
+	      if (!REG_P (XEXP (this_rtx, 0))
+		  || !HARD_REGISTER_P (XEXP (this_rtx, 0)))
+		return false;
+	      unsigned int end_regno = END_REGNO (XEXP (this_rtx, 0));
+	      for (unsigned int regno = REGNO (XEXP (this_rtx, 0));
+		   regno < end_regno; ++regno)
+		if (bitmap_bit_p (live, regno))
+		  return false;
+	    }
+	}
+      validate_change (insn, &PATTERN (insn), copy_rtx (PATTERN (other_insn)),
+		       1);
+      set = single_set_for_csa (insn);
+      validate_change (insn, &XEXP (SET_SRC (set), 1), GEN_INT (new_adjust),
+		       1);
+      remove_equal = true;
+    }
   else
     validate_change (insn, &XEXP (SET_SRC (set), 1), GEN_INT (new_adjust), 1);
 
@@ -256,10 +302,12 @@ try_apply_stack_adjustment (rtx_insn *insn, struct csa_reflist *reflist,
       for (ml = reflist; ml ; ml = ml->next)
 	ml->sp_offset -= delta;
 
-      return 1;
+      if (remove_equal)
+	remove_reg_equal_equiv_notes (insn);
+      return true;
     }
   else
-    return 0;
+    return false;
 }
 
 /* For non-debug insns, record all stack memory references in INSN
@@ -489,16 +537,21 @@ force_move_args_size_note (basic_block bb, rtx_insn *prev, rtx_insn *insn)
 /* Subroutine of combine_stack_adjustments, called for each basic block.  */
 
 static void
-combine_stack_adjustments_for_block (basic_block bb)
+combine_stack_adjustments_for_block (basic_block bb, bitmap live)
 {
   HOST_WIDE_INT last_sp_adjust = 0;
   rtx_insn *last_sp_set = NULL;
   rtx_insn *last2_sp_set = NULL;
+  bitmap last_sp_live = NULL;
   struct csa_reflist *reflist = NULL;
+  bitmap copy = NULL;
   rtx_insn *insn, *next;
   rtx set;
   bool end_of_block = false;
 
+  bitmap_copy (live, DF_LR_IN (bb));
+  df_simulate_initialize_forwards (bb, live);
+
   for (insn = BB_HEAD (bb); !end_of_block ; insn = next)
     {
       end_of_block = insn == BB_END (bb);
@@ -514,21 +567,43 @@ combine_stack_adjustments_for_block (basic_block bb)
 	{
 	  rtx dest = SET_DEST (set);
 	  rtx src = SET_SRC (set);
+	  HOST_WIDE_INT this_adjust = 0;
 
 	  /* Find constant additions to the stack pointer.  */
 	  if (dest == stack_pointer_rtx
 	      && GET_CODE (src) == PLUS
 	      && XEXP (src, 0) == stack_pointer_rtx
 	      && CONST_INT_P (XEXP (src, 1)))
+	    this_adjust = INTVAL (XEXP (src, 1));
+	  /* Or such additions turned by postreload into a store of
+	     equivalent register.  */
+	  else if (dest == stack_pointer_rtx
+		   && REG_P (src)
+		   && REGNO (src) != STACK_POINTER_REGNUM)
+	    if (rtx equal = find_reg_note (insn, REG_EQUAL, NULL_RTX))
+	      if (GET_CODE (XEXP (equal, 0)) == PLUS
+		  && XEXP (XEXP (equal, 0), 0) == stack_pointer_rtx
+		  && CONST_INT_P (XEXP (XEXP (equal, 0), 1)))
+		this_adjust = INTVAL (XEXP (XEXP (equal, 0), 1));
+
+	  if (this_adjust)
 	    {
-	      HOST_WIDE_INT this_adjust = INTVAL (XEXP (src, 1));
-
 	      /* If we've not seen an adjustment previously, record
 		 it now and continue.  */
 	      if (! last_sp_set)
 		{
 		  last_sp_set = insn;
 		  last_sp_adjust = this_adjust;
+		  if (REG_P (src))
+		    {
+		      if (copy == NULL)
+			copy = BITMAP_ALLOC (&reg_obstack);
+		      last_sp_live = copy;
+		      bitmap_copy (last_sp_live, live);
+		    }
+		  else
+		    last_sp_live = NULL;
+		  df_simulate_one_insn_forwards (bb, insn, live);
 		  continue;
 		}
 
@@ -560,13 +635,16 @@ combine_stack_adjustments_for_block (basic_block bb)
 		      && try_apply_stack_adjustment (last_sp_set, reflist,
 						     last_sp_adjust
 						     + this_adjust,
-						     this_adjust))
+						     this_adjust,
+						     last_sp_live,
+						     insn))
 		    {
 		      /* It worked!  */
 		      maybe_move_args_size_note (last_sp_set, insn, false);
 		      maybe_merge_cfa_adjust (last_sp_set, insn, false);
 		      delete_insn (insn);
 		      last_sp_adjust += this_adjust;
+		      last_sp_live = NULL;
 		      continue;
 		    }
 		}
@@ -577,10 +655,12 @@ combine_stack_adjustments_for_block (basic_block bb)
 		       ? last_sp_adjust >= 0 : last_sp_adjust <= 0)
 		{
 		  if (no_unhandled_cfa (last_sp_set)
+		      && !REG_P (src)
 		      && try_apply_stack_adjustment (insn, reflist,
 						     last_sp_adjust
 						     + this_adjust,
-						     -last_sp_adjust))
+						     -last_sp_adjust,
+						     NULL, NULL))
 		    {
 		      /* It worked!  */
 		      maybe_move_args_size_note (insn, last_sp_set, true);
@@ -588,8 +668,10 @@ combine_stack_adjustments_for_block (basic_block bb)
 		      delete_insn (last_sp_set);
 		      last_sp_set = insn;
 		      last_sp_adjust += this_adjust;
+		      last_sp_live = NULL;
 		      free_csa_reflist (reflist);
 		      reflist = NULL;
+		      df_simulate_one_insn_forwards (bb, insn, live);
 		      continue;
 		    }
 		}
@@ -612,6 +694,16 @@ combine_stack_adjustments_for_block (basic_block bb)
 	      reflist = NULL;
 	      last_sp_set = insn;
 	      last_sp_adjust = this_adjust;
+	      if (REG_P (src))
+		{
+		  if (copy == NULL)
+		    copy = BITMAP_ALLOC (&reg_obstack);
+		  last_sp_live = copy;
+		  bitmap_copy (last_sp_live, live);
+		}
+	      else
+		last_sp_live = NULL;
+	      df_simulate_one_insn_forwards (bb, insn, live);
 	      continue;
 	    }
 
@@ -641,7 +733,8 @@ combine_stack_adjustments_for_block (basic_block bb)
 	      && !reg_mentioned_p (stack_pointer_rtx, src)
 	      && memory_address_p (GET_MODE (dest), stack_pointer_rtx)
 	      && try_apply_stack_adjustment (insn, reflist, 0,
-					     -last_sp_adjust))
+					     -last_sp_adjust,
+					     NULL, NULL))
 	    {
 	      if (last2_sp_set)
 		maybe_move_args_size_note (last2_sp_set, last_sp_set, false);
@@ -652,13 +745,17 @@ combine_stack_adjustments_for_block (basic_block bb)
 	      reflist = NULL;
 	      last_sp_set = NULL;
 	      last_sp_adjust = 0;
+	      last_sp_live = NULL;
+	      df_simulate_one_insn_forwards (bb, insn, live);
 	      continue;
 	    }
 	}
 
-      if (!CALL_P (insn) && last_sp_set
-	  && record_stack_refs (insn, &reflist))
-	continue;
+      if (!CALL_P (insn) && last_sp_set && record_stack_refs (insn, &reflist))
+	{
+	  df_simulate_one_insn_forwards (bb, insn, live);
+	  continue;
+	}
 
       /* Otherwise, we were not able to process the instruction.
 	 Do not continue collecting data across such a one.  */
@@ -676,7 +773,10 @@ combine_stack_adjustments_for_block (basic_block bb)
 	  last2_sp_set = NULL;
 	  last_sp_set = NULL;
 	  last_sp_adjust = 0;
+	  last_sp_live = NULL;
 	}
+
+      df_simulate_one_insn_forwards (bb, insn, live);
     }
 
   if (last_sp_set && last_sp_adjust == 0)
@@ -687,6 +787,8 @@ combine_stack_adjustments_for_block (basic_block bb)
 
   if (reflist)
     free_csa_reflist (reflist);
+  if (copy)
+    BITMAP_FREE (copy);
 }
 
 static unsigned int