[PATCH] Fix ifcvt one_cmpl_abs optimization (PR rtl-optimization/68376)

[PATCH] Fix ifcvt one_cmpl_abs optimization (PR rtl-optimization/68376)

[Jakub Jelinek]

Hi!

noce_try_abs optimizes these cases normal abs, which doesn't really
care if the original condition is x < 0 ? -x : x or x <= 0 ? -x : x,
but also the x < 0 ? ~x : x case.  But in this case it is significant
whether for x == 0 ~x or x applies; the following patch limits the
one_cmpl optimization to those cases where the optimized expression
computes the same value.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk/5.3?

2015-11-18  Jakub Jelinek  <jakub@redhat.com>

	PR rtl-optimization/68376
	* ifcvt.c (noce_try_abs): Disable one_cmpl optimization if
	encountering x <= 0 ? ~x : x or x > 0 ? ~x : x.

	* gcc.c-torture/execute/pr68376-1.c: New test.
	* gcc.c-torture/execute/pr68376-2.c: New test.

--- gcc/ifcvt.c.jj	2015-11-14 19:35:54.000000000 +0100
+++ gcc/ifcvt.c	2015-11-18 11:02:48.645771477 +0100
@@ -2595,12 +2595,49 @@ noce_try_abs (struct noce_if_info *if_in
 
   /* Work around funny ideas get_condition has wrt canonicalization.
      Note that these rtx constants are known to be CONST_INT, and
-     therefore imply integer comparisons.  */
+     therefore imply integer comparisons.
+     The one_cmpl case is more complicated, as we want to handle
+     only x < 0 ? ~x : x or x >= 0 ? ~x : x but not
+     x <= 0 ? ~x : x or x > 0 ? ~x : x, as the latter two
+     have different result for x == 0.  */
   if (c == constm1_rtx && GET_CODE (cond) == GT)
-    ;
+    {
+      if (one_cmpl && negate)
+	return FALSE;
+    }
   else if (c == const1_rtx && GET_CODE (cond) == LT)
-    ;
-  else if (c != CONST0_RTX (GET_MODE (b)))
+    {
+      if (one_cmpl && !negate)
+	return FALSE;
+    }
+  else if (c == CONST0_RTX (GET_MODE (b)))
+    {
+      if (one_cmpl)
+	switch (GET_CODE (cond))
+	  {
+	  case GT:
+	    if (!negate)
+	      return FALSE;
+	    break;
+	  case GE:
+	    /* >= 0 is the same case as above > -1.  */
+	    if (negate)
+	      return FALSE;
+	    break;
+	  case LT:
+	    if (negate)
+	      return FALSE;
+	    break;
+	  case LE:
+	    /* <= 0 is the same case as above < 1.  */
+	    if (!negate)
+	      return FALSE;
+	    break;
+	  default:
+	    return FALSE;
+	  }
+    }
+  else
     return FALSE;
 
   /* Determine what sort of operation this is.  */
--- gcc/testsuite/gcc.c-torture/execute/pr68376-1.c.jj	2015-11-18 11:12:33.251522987 +0100
+++ gcc/testsuite/gcc.c-torture/execute/pr68376-1.c	2015-11-18 11:12:24.000000000 +0100
@@ -0,0 +1,24 @@
+/* PR rtl-optimization/68376 */
+
+int a, b, c = 1;
+signed char d;
+
+int
+main ()
+{
+  for (; a < 1; a++)
+    for (; b < 1; b++)
+      {
+	signed char e = ~d;
+	if (d < 1)
+	  e = d;
+	d = e;
+	if (!c)
+	  __builtin_abort ();
+      }
+
+  if (d != 0)
+    __builtin_abort ();
+
+  return 0;
+}
--- gcc/testsuite/gcc.c-torture/execute/pr68376-2.c.jj	2015-11-18 11:12:36.209481252 +0100
+++ gcc/testsuite/gcc.c-torture/execute/pr68376-2.c	2015-11-18 11:10:55.000000000 +0100
@@ -0,0 +1,41 @@
+/* PR rtl-optimization/68376 */
+
+extern void abort (void);
+
+__attribute__((noinline, noclone)) int
+f1 (int x)
+{
+  return x < 0 ? ~x : x;
+}
+
+__attribute__((noinline, noclone)) int
+f2 (int x)
+{
+  return x < 0 ? x : ~x;
+}
+
+__attribute__((noinline, noclone)) int
+f3 (int x)
+{
+  return x <= 0 ? ~x : x;
+}
+
+__attribute__((noinline, noclone)) int
+f4 (int x)
+{
+  return x <= 0 ? x : ~x;
+}
+
+int
+main ()
+{
+  if (f1 (5) != 5 || f1 (-5) != 4 || f1 (0) != 0)
+    abort ();
+  if (f2 (5) != -6 || f2 (-5) != -5 || f2 (0) != -1)
+    abort ();
+  if (f3 (5) != 5 || f3 (-5) != 4 || f3 (0) != -1)
+    abort ();
+  if (f4 (5) != -6 || f4 (-5) != -5 || f4 (0) != 0)
+    abort ();
+  return 0;
+}

	Jakub

Re: [PATCH] Fix ifcvt one_cmpl_abs optimization (PR rtl-optimization/68376)

[Bernd Schmidt]

On 11/18/2015 11:44 PM, Jakub Jelinek wrote:
> noce_try_abs optimizes these cases normal abs, which doesn't really
> care if the original condition is x < 0 ? -x : x or x <= 0 ? -x : x,
> but also the x < 0 ? ~x : x case.  But in this case it is significant
> whether for x == 0 ~x or x applies; the following patch limits the
> one_cmpl optimization to those cases where the optimized expression
> computes the same value.

Ok.


Bernd