[PATCH] avoid cselib rtx_equal_for_cselib_1 infinite recursion (PR debug/80025)

[Jakub Jelinek <jakub at redhat dot com>]

Hi!

On Thu, Mar 23, 2017 at 03:00:04PM +0100, Jakub Jelinek wrote:
> On Tue, Mar 21, 2017 at 07:43:51PM -0300, Alexandre Oliva wrote:
> > When two VALUEs are recorded in the cselib equivalence table such that
> > they are equivalent to each other XORed with the same expression, if
> > we started a cselib equivalence test between say the odd one and the
> > even one, we'd end up recursing to compare the even one with the odd
> > one, and then again, indefinitely.
> > 
> > This patch cuts off this infinite recursion by recognizing the XOR
> > special case (it's the only binary commutative operation in which
> > applying one of the operands of an operation to the result of that
> > operation brings you back to the other operand) and determining
> > whether we have an equivalence without recursing down the infinite
> > path.
> 
> Is XOR the only special case though?  E.g. PLUS or MINUS with
> the most negative constant act the same, and I don't see why if unlucky
> enough with reverse ops etc. you couldn't get something similar through
> combination thereof, perhaps indirectly through multiple VALUEs.
> 
> So I think it is safer to just put a cap on the rtx_equal_for_cselib_1
> recursion depth (should be enough to bump the depth only when walking
> locs of a VALUE).  I'll test such a patch.

Here is that patch, bootstrapped/regtested on x86_64-linux and i686-linux,
ok for trunk?  Or shall I turn that 128 into a --param?

2017-03-23  Jakub Jelinek  <jakub@redhat.com>

	PR debug/80025
	* cselib.h (rtx_equal_for_cselib_1): Add depth argument.
	(rtx_equal_for_cselib_p): Pass 0 to it.
	* cselib.c (cselib_hasher::equal): Likewise.
	(rtx_equal_for_cselib_1): Add depth argument.  If depth
	is 128, don't look up VALUE locs and punt.  Increment
	depth in recursive calls when walking VALUE locs.

	* gcc.dg/torture/pr80025.c: New test.

--- gcc/cselib.h.jj	2017-01-01 12:45:37.000000000 +0100
+++ gcc/cselib.h	2017-03-23 14:06:35.348504435 +0100
@@ -82,7 +82,7 @@ extern void cselib_finish (void);
 extern void cselib_process_insn (rtx_insn *);
 extern bool fp_setter_insn (rtx_insn *);
 extern machine_mode cselib_reg_set_mode (const_rtx);
-extern int rtx_equal_for_cselib_1 (rtx, rtx, machine_mode);
+extern int rtx_equal_for_cselib_1 (rtx, rtx, machine_mode, int);
 extern int references_value_p (const_rtx, int);
 extern rtx cselib_expand_value_rtx (rtx, bitmap, int);
 typedef rtx (*cselib_expand_callback)(rtx, bitmap, int, void *);
@@ -134,7 +134,7 @@ rtx_equal_for_cselib_p (rtx x, rtx y)
   if (x == y)
     return 1;
 
-  return rtx_equal_for_cselib_1 (x, y, VOIDmode);
+  return rtx_equal_for_cselib_1 (x, y, VOIDmode, 0);
 }
 
 #endif /* GCC_CSELIB_H */
--- gcc/cselib.c.jj	2017-01-01 12:45:39.000000000 +0100
+++ gcc/cselib.c	2017-03-23 14:38:50.238487353 +0100
@@ -125,7 +125,7 @@ cselib_hasher::equal (const cselib_val *
   /* We don't guarantee that distinct rtx's have different hash values,
      so we need to do a comparison.  */
   for (l = v->locs; l; l = l->next)
-    if (rtx_equal_for_cselib_1 (l->loc, x, memmode))
+    if (rtx_equal_for_cselib_1 (l->loc, x, memmode, 0))
       {
 	promote_debug_loc (l);
 	return true;
@@ -834,7 +834,7 @@ autoinc_split (rtx x, rtx *off, machine_
    addresses, MEMMODE should be VOIDmode.  */
 
 int
-rtx_equal_for_cselib_1 (rtx x, rtx y, machine_mode memmode)
+rtx_equal_for_cselib_1 (rtx x, rtx y, machine_mode memmode, int depth)
 {
   enum rtx_code code;
   const char *fmt;
@@ -867,6 +867,9 @@ rtx_equal_for_cselib_1 (rtx x, rtx y, ma
       if (GET_CODE (y) == VALUE)
 	return e == canonical_cselib_val (CSELIB_VAL_PTR (y));
 
+      if (depth == 128)
+	return 0;
+
       for (l = e->locs; l; l = l->next)
 	{
 	  rtx t = l->loc;
@@ -876,7 +879,7 @@ rtx_equal_for_cselib_1 (rtx x, rtx y, ma
 	     list.  */
 	  if (REG_P (t) || MEM_P (t) || GET_CODE (t) == VALUE)
 	    continue;
-	  else if (rtx_equal_for_cselib_1 (t, y, memmode))
+	  else if (rtx_equal_for_cselib_1 (t, y, memmode, depth + 1))
 	    return 1;
 	}
 
@@ -887,13 +890,16 @@ rtx_equal_for_cselib_1 (rtx x, rtx y, ma
       cselib_val *e = canonical_cselib_val (CSELIB_VAL_PTR (y));
       struct elt_loc_list *l;
 
+      if (depth == 128)
+	return 0;
+
       for (l = e->locs; l; l = l->next)
 	{
 	  rtx t = l->loc;
 
 	  if (REG_P (t) || MEM_P (t) || GET_CODE (t) == VALUE)
 	    continue;
-	  else if (rtx_equal_for_cselib_1 (x, t, memmode))
+	  else if (rtx_equal_for_cselib_1 (x, t, memmode, depth + 1))
 	    return 1;
 	}
 
@@ -914,12 +920,12 @@ rtx_equal_for_cselib_1 (rtx x, rtx y, ma
       if (!xoff != !yoff)
 	return 0;
 
-      if (xoff && !rtx_equal_for_cselib_1 (xoff, yoff, memmode))
+      if (xoff && !rtx_equal_for_cselib_1 (xoff, yoff, memmode, depth))
 	return 0;
 
       /* Don't recurse if nothing changed.  */
       if (x != xorig || y != yorig)
-	return rtx_equal_for_cselib_1 (x, y, memmode);
+	return rtx_equal_for_cselib_1 (x, y, memmode, depth);
 
       return 0;
     }
@@ -953,7 +959,8 @@ rtx_equal_for_cselib_1 (rtx x, rtx y, ma
     case MEM:
       /* We have to compare any autoinc operations in the addresses
 	 using this MEM's mode.  */
-      return rtx_equal_for_cselib_1 (XEXP (x, 0), XEXP (y, 0), GET_MODE (x));
+      return rtx_equal_for_cselib_1 (XEXP (x, 0), XEXP (y, 0), GET_MODE (x),
+				     depth);
 
     default:
       break;
@@ -988,17 +995,20 @@ rtx_equal_for_cselib_1 (rtx x, rtx y, ma
 	  /* And the corresponding elements must match.  */
 	  for (j = 0; j < XVECLEN (x, i); j++)
 	    if (! rtx_equal_for_cselib_1 (XVECEXP (x, i, j),
-					  XVECEXP (y, i, j), memmode))
+					  XVECEXP (y, i, j), memmode, depth))
 	      return 0;
 	  break;
 
 	case 'e':
 	  if (i == 1
 	      && targetm.commutative_p (x, UNKNOWN)
-	      && rtx_equal_for_cselib_1 (XEXP (x, 1), XEXP (y, 0), memmode)
-	      && rtx_equal_for_cselib_1 (XEXP (x, 0), XEXP (y, 1), memmode))
+	      && rtx_equal_for_cselib_1 (XEXP (x, 1), XEXP (y, 0), memmode,
+					 depth)
+	      && rtx_equal_for_cselib_1 (XEXP (x, 0), XEXP (y, 1), memmode,
+					 depth))
 	    return 1;
-	  if (! rtx_equal_for_cselib_1 (XEXP (x, i), XEXP (y, i), memmode))
+	  if (! rtx_equal_for_cselib_1 (XEXP (x, i), XEXP (y, i), memmode,
+					depth))
 	    return 0;
 	  break;
 
--- gcc/testsuite/gcc.dg/torture/pr80025.c.jj	2017-03-23 14:44:34.801024681 +0100
+++ gcc/testsuite/gcc.dg/torture/pr80025.c	2017-03-23 14:43:54.000000000 +0100
@@ -0,0 +1,24 @@
+/* PR debug/80025 */
+/* { dg-do compile } */
+/* { dg-options "-g -ftracer -w" } */
+
+int a;
+long int b, c;
+
+long int
+foo (void)
+{
+}
+
+void
+bar (int x, short int y, unsigned short int z)
+{
+}
+
+int
+baz (void)
+{
+  a -= b;
+  b = !foo ();
+  bar (b ^= (c ^ 1) ? (c ^ 1) : foo (), (__INTPTR_TYPE__) &bar, a);
+}


	Jakub