[PATCH v4 1/3] [RFC] ifcvt: handle sequences that clobber flags in noce_convert_multiple_sets

[Manolis Tsamis <manolis.tsamis@vrull.eu>]

This is an extension of what was done in PR106590.

Currently if a sequence generated in noce_convert_multiple_sets clobbers the
condition rtx (cc_cmp or rev_cc_cmp) then only seq1 is used afterwards
(sequences that emit the comparison itself). Since this applies only from the
next iteration it assumes that the sequences generated (in particular seq2)
doesn't clobber the condition rtx itself before using it in the if_then_else,
which is only true in specific cases (currently only register/subregister moves
are allowed).

This patch changes this so it also tests if seq2 clobbers cc_cmp/rev_cc_cmp in
the current iteration. This makes it possible to include arithmetic operations
in noce_convert_multiple_sets.

It also makes the code that checks whether the condition is used outside of the
if_then_else emitted more robust.

gcc/ChangeLog:

	* ifcvt.cc (check_for_cc_cmp_clobbers): Use modified_in_p instead.
	(noce_convert_multiple_sets_1): Don't use seq2 if it clobbers cc_cmp.
	Refactor the code that sets read_comparison.

Signed-off-by: Manolis Tsamis <manolis.tsamis@vrull.eu>
---

(no changes since v1)

 gcc/ifcvt.cc | 106 ++++++++++++++++++++++++++++-----------------------
 1 file changed, 59 insertions(+), 47 deletions(-)

diff --git a/gcc/ifcvt.cc b/gcc/ifcvt.cc
index 58ed42673e5..763a25f816e 100644
--- a/gcc/ifcvt.cc
+++ b/gcc/ifcvt.cc
@@ -3592,20 +3592,6 @@ noce_convert_multiple_sets (struct noce_if_info *if_info)
   return true;
 }
 
-/* Helper function for noce_convert_multiple_sets_1.  If store to
-   DEST can affect P[0] or P[1], clear P[0].  Called via note_stores.  */
-
-static void
-check_for_cc_cmp_clobbers (rtx dest, const_rtx, void *p0)
-{
-  rtx *p = (rtx *) p0;
-  if (p[0] == NULL_RTX)
-    return;
-  if (reg_overlap_mentioned_p (dest, p[0])
-      || (p[1] && reg_overlap_mentioned_p (dest, p[1])))
-    p[0] = NULL_RTX;
-}
-
 /* This goes through all relevant insns of IF_INFO->then_bb and tries to
    create conditional moves.  In case a simple move sufficis the insn
    should be listed in NEED_NO_CMOV.  The rewired-src cases should be
@@ -3731,36 +3717,67 @@ noce_convert_multiple_sets_1 (struct noce_if_info *if_info,
 	 creating an additional compare for each.  If successful, costing
 	 is easier and this sequence is usually preferred.  */
       if (cc_cmp)
-	seq2 = try_emit_cmove_seq (if_info, temp, cond,
-				   new_val, old_val, need_cmov,
-				   &cost2, &temp_dest2, cc_cmp, rev_cc_cmp);
+	{
+	  seq2 = try_emit_cmove_seq (if_info, temp, cond,
+				     new_val, old_val, need_cmov,
+				     &cost2, &temp_dest2, cc_cmp, rev_cc_cmp);
+
+	  /* The if_then_else in SEQ2 may be affected when cc_cmp/rev_cc_cmp is
+	     clobbered.  We can't safely use the sequence in this case.  */
+	  if (seq2 && (modified_in_p (cc_cmp, seq2)
+	      || (rev_cc_cmp && modified_in_p (rev_cc_cmp, seq2))))
+	    seq2 = NULL;
+	}
 
       /* The backend might have created a sequence that uses the
-	 condition.  Check this.  */
+	 condition as a value.  Check this.  */
+
+      /* We cannot handle anything more complex than a reg or constant.  */
+      if (!REG_P (XEXP (cond, 0)) && !CONSTANT_P (XEXP (cond, 0)))
+	read_comparison = true;
+
+      if (!REG_P (XEXP (cond, 1)) && !CONSTANT_P (XEXP (cond, 1)))
+	read_comparison = true;
+
       rtx_insn *walk = seq2;
-      while (walk)
+      int if_then_else_count = 0;
+      while (walk && !read_comparison)
 	{
-	  rtx set = single_set (walk);
+	  rtx exprs_to_check[2];
+	  unsigned int exprs_count = 0;
 
-	  if (!set || !SET_SRC (set))
+	  rtx set = single_set (walk);
+	  if (set && XEXP (set, 1)
+	      && GET_CODE (XEXP (set, 1)) == IF_THEN_ELSE)
 	    {
-	      walk = NEXT_INSN (walk);
-	      continue;
+	      /* We assume that this is the cmove created by the backend that
+		 naturally uses the condition.  */
+	      exprs_to_check[exprs_count++] = XEXP (XEXP (set, 1), 1);
+	      exprs_to_check[exprs_count++] = XEXP (XEXP (set, 1), 2);
+	      if_then_else_count++;
 	    }
+	  else if (NONDEBUG_INSN_P (walk))
+	    exprs_to_check[exprs_count++] = PATTERN (walk);
 
-	  rtx src = SET_SRC (set);
+	  /* Bail if we get more than one if_then_else because the assumption
+	     above may be incorrect.  */
+	  if (if_then_else_count > 1)
+	    {
+	      read_comparison = true;
+	      break;
+	    }
 
-	  if (XEXP (set, 1) && GET_CODE (XEXP (set, 1)) == IF_THEN_ELSE)
-	    ; /* We assume that this is the cmove created by the backend that
-		 naturally uses the condition.  Therefore we ignore it.  */
-	  else
+	  for (unsigned int i = 0; i < exprs_count; i++)
 	    {
-	      if (reg_mentioned_p (XEXP (cond, 0), src)
-		  || reg_mentioned_p (XEXP (cond, 1), src))
-		{
-		  read_comparison = true;
-		  break;
-		}
+	      subrtx_iterator::array_type array;
+	      FOR_EACH_SUBRTX (iter, array, exprs_to_check[i], NONCONST)
+		if (*iter != NULL_RTX
+		    && (reg_overlap_mentioned_p (XEXP (cond, 0), *iter)
+		    || reg_overlap_mentioned_p (XEXP (cond, 1), *iter)))
+		  {
+		    read_comparison = true;
+		    break;
+		  }
 	    }
 
 	  walk = NEXT_INSN (walk);
@@ -3788,21 +3805,16 @@ noce_convert_multiple_sets_1 (struct noce_if_info *if_info,
 	  return false;
 	}
 
-      if (cc_cmp)
+      if (cc_cmp && seq == seq1)
 	{
-	  /* Check if SEQ can clobber registers mentioned in
-	     cc_cmp and/or rev_cc_cmp.  If yes, we need to use
-	     only seq1 from that point on.  */
-	  rtx cc_cmp_pair[2] = { cc_cmp, rev_cc_cmp };
-	  for (walk = seq; walk; walk = NEXT_INSN (walk))
+	  /* Check if SEQ can clobber registers mentioned in cc_cmp/rev_cc_cmp.
+	     If yes, we need to use only seq1 from that point on.
+	     Only check when we use seq1 since we have already tested seq2.  */
+	  if (modified_in_p (cc_cmp, seq)
+	      || (rev_cc_cmp && modified_in_p (rev_cc_cmp, seq)))
 	    {
-	      note_stores (walk, check_for_cc_cmp_clobbers, cc_cmp_pair);
-	      if (cc_cmp_pair[0] == NULL_RTX)
-		{
-		  cc_cmp = NULL_RTX;
-		  rev_cc_cmp = NULL_RTX;
-		  break;
-		}
+	      cc_cmp = NULL_RTX;
+	      rev_cc_cmp = NULL_RTX;
 	    }
 	}
 
-- 
2.34.1