cse: Use simplify_replace_fn_rtx to process notes [PR94740]

cse_process_notes did a very simple substitution, which in the wrong
circumstances could create non-canonical RTL and invalid MEMs.
Various sticking plasters have been applied to cse_process_notes_1
to handle cases like ZERO_EXTEND, SIGN_EXTEND and UNSIGNED_FLOAT,
but I think this PR is a plaster too far.

The code is trying hard to avoid creating unnecessary rtl, which of
course is a good thing.  If we continue to do that, then we can end
up changing subexpressions while keeping the containing rtx.
This in turn means that validate_change will be a no-op on the
containing rtx, even if its contents have changed.  So in these
cases we have to apply validate_change to the individual subexpressions.

On the other hand, if we always apply validate_change to the
individual subexpressions, we'll end up calling validate_change
on something before it has been simplified and canonicalised.
And that's one of the situations we're trying to avoid.

There might be a middle ground in which we queue the validate_changes
as part of a group, and so can cancel the pending validate_changes
for subexpressions if there's a change in the outer expression.
But that seems even more ad-hoc than the current code.
It would also be quite an invasive change.

I think the best thing is just to hook into the existing
simplify_replace_fn_rtx function, keeping the REG and MEM handling
from cse_process_notes_1 essentially unchanged.  It can generate
more redundant rtl when a simplification takes place, but it has
the advantage of being relative well-used code (both directly
and via simplify_replace_rtx).

2020-04-30  Richard Sandiford  <richard.sandiford@arm.com>

gcc/
	PR rtl-optimization/94740
	* cse.c (cse_process_notes_1): Replace with...
	(cse_process_note_1): ...this new function, acting as a
	simplify_replace_fn_rtx callback to process_note.  Handle only
	REGs and MEMs directly.  Validate the MEM if cse_process_note
	changes its address.
	(cse_process_notes): Replace with...
	(cse_process_note): ...this new function.
	(cse_extended_basic_block): Update accordingly, iterating over
	the register notes and passing individual notes to cse_process_note.

gcc/ChangeLog

+2020-04-30  Richard Sandiford  <richard.sandiford@arm.com>
+
+	PR rtl-optimization/94740
+	* cse.c (cse_process_notes_1): Replace with...
+	(cse_process_note_1): ...this new function, acting as a
+	simplify_replace_fn_rtx callback to process_note.  Handle only
+	REGs and MEMs directly.  Validate the MEM if cse_process_note
+	changes its address.
+	(cse_process_notes): Replace with...
+	(cse_process_note): ...this new function.
+	(cse_extended_basic_block): Update accordingly, iterating over
+	the register notes and passing individual notes to cse_process_note.
+
 2020-04-30  Martin Jambor  <mjambor@suse.cz>
 
 	PR ipa/94856

gcc/cse.c

@@ -585,7 +585,6 @@ static void cse_insn (rtx_insn *);
 static void cse_prescan_path (struct cse_basic_block_data *);
 static void invalidate_from_clobbers (rtx_insn *);
 static void invalidate_from_sets_and_clobbers (rtx_insn *);
-static rtx cse_process_notes (rtx, rtx, bool *);
 static void cse_extended_basic_block (struct cse_basic_block_data *);
 extern void dump_class (struct table_elt*);
 static void get_cse_reg_info_1 (unsigned int regno);
@@ -6222,75 +6221,28 @@ invalidate_from_sets_and_clobbers (rtx_insn *insn)
     }
 }
 
-/* Process X, part of the REG_NOTES of an insn.  Look at any REG_EQUAL notes
-   and replace any registers in them with either an equivalent constant
-   or the canonical form of the register.  If we are inside an address,
-   only do this if the address remains valid.
+static rtx cse_process_note (rtx);
 
-   OBJECT is 0 except when within a MEM in which case it is the MEM.
+/* A simplify_replace_fn_rtx callback for cse_process_note.  Process X,
+   part of the REG_NOTES of an insn.  Replace any registers with either
+   an equivalent constant or the canonical form of the register.
+   Only replace addresses if the containing MEM remains valid.
 
-   Return the replacement for X.  */
+   Return the replacement for X, or null if it should be simplified
+   recursively.  */
 
 static rtx
-cse_process_notes_1 (rtx x, rtx object, bool *changed)
+cse_process_note_1 (rtx x, const_rtx, void *)
 {
-  enum rtx_code code = GET_CODE (x);
-  const char *fmt = GET_RTX_FORMAT (code);
-  int i;
-
-  switch (code)
-    {
-    case CONST:
-    case SYMBOL_REF:
-    case LABEL_REF:
-    CASE_CONST_ANY:
-    case PC:
-    case CC0:
-    case LO_SUM:
-      return x;
-
-    case MEM:
-      validate_change (x, &XEXP (x, 0),
-		       cse_process_notes (XEXP (x, 0), x, changed), 0);
-      return x;
-
-    case EXPR_LIST:
-      if (REG_NOTE_KIND (x) == REG_EQUAL)
-	XEXP (x, 0) = cse_process_notes (XEXP (x, 0), NULL_RTX, changed);
-      /* Fall through.  */
-
-    case INSN_LIST:
-    case INT_LIST:
-      if (XEXP (x, 1))
-	XEXP (x, 1) = cse_process_notes (XEXP (x, 1), NULL_RTX, changed);
-      return x;
-
-    case SIGN_EXTEND:
-    case ZERO_EXTEND:
-    case SUBREG:
+  if (MEM_P (x))
     {
-	rtx new_rtx = cse_process_notes (XEXP (x, 0), object, changed);
-	/* We don't substitute VOIDmode constants into these rtx,
-	   since they would impede folding.  */
-	if (GET_MODE (new_rtx) != VOIDmode)
-	  validate_change (object, &XEXP (x, 0), new_rtx, 0);
+      validate_change (x, &XEXP (x, 0), cse_process_note (XEXP (x, 0)), false);
       return x;
     }
 
-    case UNSIGNED_FLOAT:
+  if (REG_P (x))
     {
-	rtx new_rtx = cse_process_notes (XEXP (x, 0), object, changed);
-	/* We don't substitute negative VOIDmode constants into these rtx,
-	   since they would impede folding.  */
-	if (GET_MODE (new_rtx) != VOIDmode
-	    || (CONST_INT_P (new_rtx) && INTVAL (new_rtx) >= 0)
-	    || (CONST_DOUBLE_P (new_rtx) && CONST_DOUBLE_HIGH (new_rtx) >= 0))
-	  validate_change (object, &XEXP (x, 0), new_rtx, 0);
-	return x;
-      }
-
-    case REG:
-      i = REG_QTY (REGNO (x));
+      int i = REG_QTY (REGNO (x));
 
       /* Return a constant or a constant register.  */
       if (REGNO_QTY_VALID_P (REGNO (x)))
@@ -6309,26 +6261,19 @@ cse_process_notes_1 (rtx x, rtx object, bool *changed)
 
       /* Otherwise, canonicalize this register.  */
       return canon_reg (x, NULL);
-
-    default:
-      break;
     }
 
-  for (i = 0; i < GET_RTX_LENGTH (code); i++)
-    if (fmt[i] == 'e')
-      validate_change (object, &XEXP (x, i),
-		       cse_process_notes (XEXP (x, i), object, changed), 0);
-
-  return x;
+  return NULL_RTX;
 }
 
+/* Process X, part of the REG_NOTES of an insn.  Replace any registers in it
+   with either an equivalent constant or the canonical form of the register.
+   Only replace addresses if the containing MEM remains valid.  */
+
 static rtx
-cse_process_notes (rtx x, rtx object, bool *changed)
+cse_process_note (rtx x)
 {
-  rtx new_rtx = cse_process_notes_1 (x, object, changed);
-  if (new_rtx != x)
-    *changed = true;
-  return new_rtx;
+  return simplify_replace_fn_rtx (x, NULL_RTX, cse_process_note_1, NULL);
 }
 
 
@@ -6623,14 +6568,19 @@ cse_extended_basic_block (struct cse_basic_block_data *ebb_data)
 	    {
 	      /* Process notes first so we have all notes in canonical forms
 		 when looking for duplicate operations.  */
-	      if (REG_NOTES (insn))
-		{
 	      bool changed = false;
-		  REG_NOTES (insn) = cse_process_notes (REG_NOTES (insn),
-						        NULL_RTX, &changed);
+	      for (rtx note = REG_NOTES (insn); note; note = XEXP (note, 1))
+		if (REG_NOTE_KIND (note) == REG_EQUAL)
+		  {
+		    rtx newval = cse_process_note (XEXP (note, 0));
+		    if (newval != XEXP (note, 0))
+		      {
+			XEXP (note, 0) = newval;
+			changed = true;
+		      }
+		  }
 	      if (changed)
 		df_notes_rescan (insn);
-		}
 
 	      cse_insn (insn);