[Bug tree-optimization/58662] wrong code at -O2 and -O3 on x86_64-linux-gnu (in 64-bit mode)

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58662

Richard Biener rguenth at gcc dot gnu.org changed:

   What|Removed |Added

 Status|NEW |ASSIGNED
   Assignee|unassigned at gcc dot gnu.org  |rguenth at gcc dot 
gnu.org

--- Comment #4 from Richard Biener rguenth at gcc dot gnu.org ---
I will have a looksee.

[Bug tree-optimization/58662] wrong code at -O2 and -O3 on x86_64-linux-gnu (in 64-bit mode)

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58662

--- Comment #5 from Richard Biener rguenth at gcc dot gnu.org ---
It looks like changing the testcase line

  d = foo (a == 0, (0, 35536)); 

to

  d = foo (a == 0, -3);  

fixes it.  _No_ IL difference in 065t.mergephi2, but then 066t.vrp1 has

 main ()
 {
   char e;
@@ -39,6 +35,7 @@
   _Bool _4;
   int _5;
   int _7;
+  int c.4_9;
   int b.5_11;
   int _12;

@@ -46,22 +43,37 @@
   a.0_3 = a;
   _4 = a.0_3 == 0;
   _5 = (int) _4;
-  _12 = 0;
-  d = 0;
-  _7 = 0;
-  e_8 = 0;
-  iftmp.3_1 = 0;
-  b ={v} 0;
-  b.5_11 ={v} b;
-  if (b.5_11 != 0)
+  _12 = _5 / -3;
+  d = _12;
+  _7 = _12 % 14;
+  e_8 = (char) _7;
+  if (_7 != 0)
 goto bb 3;
   else
 goto bb 4;

   bb 3:
-  abort ();
+  c.4_9 = c;
+  if (c.4_9 != 0)
+goto bb 5;
+  else
+goto bb 4;

   bb 4:
+
+  bb 5:
+  # iftmp.3_1 = PHI 1(3), 0(4)
+  b ={v} iftmp.3_1;
+  b.5_11 ={v} b;
+  if (b.5_11 != 0)
+goto bb 6;
+  else
+goto bb 7;
+
+  bb 6:
+  abort ();
+
+  bb 7:
   return 0;

 }

what?!

Reduced testcase:

extern void abort (void);

int a, c, d;
volatile int b;

static int
foo (int p1, short p2)
{
  return p1 / p2;
}

int
main ()
{
  char e;
  d = foo (a == 0, (0, 35536)); 
  e = d % 14;
  b = e  c;
  if (b != 0)
abort ();
  return 0;
}

[Bug tree-optimization/58662] wrong code at -O2 and -O3 on x86_64-linux-gnu (in 64-bit mode)

[mpolacek at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58662

Marek Polacek mpolacek at gcc dot gnu.org changed:

   What|Removed |Added

 Status|UNCONFIRMED |NEW
   Last reconfirmed||2013-10-08
 CC||mpolacek at gcc dot gnu.org
   Target Milestone|--- |4.9.0
 Ever confirmed|0   |1

--- Comment #1 from Marek Polacek mpolacek at gcc dot gnu.org ---
Confirmed.  It seems to be the VRP; adding -fno-tree-vrp makes trunk behave as
4.8.

[Bug tree-optimization/58662] wrong code at -O2 and -O3 on x86_64-linux-gnu (in 64-bit mode)

[mpolacek at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58662

Marek Polacek mpolacek at gcc dot gnu.org changed:

   What|Removed |Added

 CC||rguenth at gcc dot gnu.org

--- Comment #2 from Marek Polacek mpolacek at gcc dot gnu.org ---
Started with r202944.

[Bug tree-optimization/58662] wrong code at -O2 and -O3 on x86_64-linux-gnu (in 64-bit mode)

[mpolacek at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58662

--- Comment #3 from Marek Polacek mpolacek at gcc dot gnu.org ---
Actually, I think it's the uncprop:

--- Q.c.139t.crited22013-10-08 13:03:04.169955615 +0200
+++ Q.c.141t.uncprop12013-10-08 13:03:04.169955615 +0200
@@ -51,7 +51,7 @@
   _13 = (int) _8;

   bb 4:
-  # iftmp.3_1 = PHI 0(5), _13(3)
+  # iftmp.3_1 = PHI _7(5), _13(3)
   b = iftmp.3_1;
   printf (%d\n, iftmp.3_1);
   return 0;

so -fno-tree-dominator-opts makes the bug go away.