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[PATCH] Adjust/remove REG_EQ{UAL,UIV} notes in REE (PR rtl-optimization/63659)


Hi!

The following testcase is miscompiled in 4.8+ on x86_64 at -O2+,
because REE widens for ZERO_EXTEND mode on
(set (reg:QI ax) (const_int -1)) instruction to SImode, but doesn't
adjust REG_EQUAL note of (const_int -1) also to (const_int 0xff)
like it changes the pattern.

The following patch attempts to adjust the notes if they are CONST_INT,
or drop otherwise (not sure if it would be desirable to emit
a ZERO_EXTEND of the previous content of the note), and both through
validate_change, so that if we give up later on, it is undone.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
What about 4.9.2 (after release) and 4.8.x?

2014-10-27  Jakub Jelinek  <jakub@redhat.com>

	PR rtl-optimization/63659
	* ree.c (update_reg_equal_equiv_notes): New function.
	(combine_set_extension, transform_ifelse): Use it.

	* gcc.c-torture/execute/pr63659.c: New test.

--- gcc/ree.c.jj	2014-10-22 15:52:18.000000000 +0200
+++ gcc/ree.c	2014-10-27 19:18:37.287412478 +0100
@@ -266,6 +266,50 @@ typedef struct ext_cand
 
 static int max_insn_uid;
 
+/* Update or remove REG_EQUAL or REG_EQUIV notes for INSN.  */
+
+static bool
+update_reg_equal_equiv_notes (rtx_insn *insn, enum machine_mode new_mode,
+			      enum machine_mode old_mode, enum rtx_code code)
+{
+  rtx *loc = &REG_NOTES (insn);
+  while (*loc)
+    {
+      enum reg_note kind = REG_NOTE_KIND (*loc);
+      if (kind == REG_EQUAL || kind == REG_EQUIV)
+	{
+	  rtx orig_src = XEXP (*loc, 0);
+	  /* Update equivalency constants.  Recall that RTL constants are
+	     sign-extended.  */
+	  if (GET_CODE (orig_src) == CONST_INT
+	      && HOST_BITS_PER_WIDE_INT >= GET_MODE_BITSIZE (new_mode))
+	    {
+	      if (INTVAL (orig_src) >= 0 || code == SIGN_EXTEND)
+		/* Nothing needed.  */;
+	      else
+		{
+		  /* Zero-extend the negative constant by masking out the
+		     bits outside the source mode.  */
+		  rtx new_const_int
+		    = gen_int_mode (INTVAL (orig_src)
+				    & GET_MODE_MASK (old_mode),
+				    new_mode);
+		  if (!validate_change (insn, &XEXP (*loc, 0),
+					new_const_int, true))
+		    return false;
+		}
+	      loc = &XEXP (*loc, 1);
+	    }
+	  /* Drop all other notes, they assume a wrong mode.  */
+	  else if (!validate_change (insn, loc, XEXP (*loc, 1), true))
+	    return false;
+	}
+      else
+	loc = &XEXP (*loc, 1);
+    }
+  return true;
+}
+
 /* Given a insn (CURR_INSN), an extension candidate for removal (CAND)
    and a pointer to the SET rtx (ORIG_SET) that needs to be modified,
    this code modifies the SET rtx to a new SET rtx that extends the
@@ -287,6 +331,7 @@ static bool
 combine_set_extension (ext_cand *cand, rtx_insn *curr_insn, rtx *orig_set)
 {
   rtx orig_src = SET_SRC (*orig_set);
+  enum machine_mode orig_mode = GET_MODE (SET_DEST (*orig_set));
   rtx new_set;
   rtx cand_pat = PATTERN (cand->insn);
 
@@ -323,9 +368,8 @@ combine_set_extension (ext_cand *cand, r
 	{
 	  /* Zero-extend the negative constant by masking out the bits outside
 	     the source mode.  */
-	  enum machine_mode src_mode = GET_MODE (SET_DEST (*orig_set));
 	  rtx new_const_int
-	    = gen_int_mode (INTVAL (orig_src) & GET_MODE_MASK (src_mode),
+	    = gen_int_mode (INTVAL (orig_src) & GET_MODE_MASK (orig_mode),
 			    GET_MODE (new_reg));
 	  new_set = gen_rtx_SET (VOIDmode, new_reg, new_const_int);
 	}
@@ -364,7 +408,9 @@ combine_set_extension (ext_cand *cand, r
 
   /* This change is a part of a group of changes.  Hence,
      validate_change will not try to commit the change.  */
-  if (validate_change (curr_insn, orig_set, new_set, true))
+  if (validate_change (curr_insn, orig_set, new_set, true)
+      && update_reg_equal_equiv_notes (curr_insn, cand->mode, orig_mode,
+				       cand->code))
     {
       if (dump_file)
         {
@@ -414,7 +460,9 @@ transform_ifelse (ext_cand *cand, rtx_in
   ifexpr = gen_rtx_IF_THEN_ELSE (cand->mode, cond, map_srcreg, map_srcreg2);
   new_set = gen_rtx_SET (VOIDmode, map_dstreg, ifexpr);
 
-  if (validate_change (def_insn, &PATTERN (def_insn), new_set, true))
+  if (validate_change (def_insn, &PATTERN (def_insn), new_set, true)
+      && update_reg_equal_equiv_notes (def_insn, cand->mode, GET_MODE (dstreg),
+				       cand->code))
     {
       if (dump_file)
         {
--- gcc/testsuite/gcc.c-torture/execute/pr63659.c.jj	2014-10-27 19:26:57.720902738 +0100
+++ gcc/testsuite/gcc.c-torture/execute/pr63659.c	2014-10-27 19:26:36.000000000 +0100
@@ -0,0 +1,29 @@
+/* PR rtl-optimization/63659 */
+
+int a, b, c, *d = &b, g, h, i;
+unsigned char e;
+char f;
+
+int
+main ()
+{
+  while (a)
+    {
+      for (a = 0; a; a++)
+	for (; c; c++)
+	  ;
+      if (i)
+	break;
+    }
+
+  char j = c, k = -1, l;
+  l = g = j >> h;
+  f = l == 0 ? k : k % l;
+  e = 0 ? 0 : f;
+  *d = e;
+
+  if (b != 255)
+    __builtin_abort ();
+
+  return 0;
+}

	Jakub


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