[Bug tree-optimization/64878] New: [5 Regression] Miscompilation of nntpgrab

[Bug tree-optimization/64878] New: [5 Regression] Miscompilation of nntpgrab

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64878

            Bug ID: 64878
           Summary: [5 Regression] Miscompilation of nntpgrab
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: tree-optimization
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jakub at gcc dot gnu.org

Starting with r218451 gcc miscompiles at -O2 on x86_64-linux (both -m64 and
-m32) following testcase:

struct A { int a1; };
struct B { char *b1; int b2; int b3; };
struct C { char *c1; int c2; struct B *c3; };
extern struct A *f1 (char *s);
static struct A *f2 (struct C *x);
__attribute__ ((noinline, noclone)) int f3 (struct A *x, struct A *z) { asm
volatile ("" : : "g" (x), "g" (z) : "memory"); return 0; }
__attribute__ ((noinline, noclone)) void f4 (struct A *x, char *y, struct A *z)
{ asm volatile ("" : : "g" (x), "g" (z), "g" (y) : "memory"); }
__attribute__ ((noinline, noclone)) struct B *f5 (void) { static char b[32];
static struct B f3 = { b, 0, 32 }; return &f3; }
__attribute__ ((noinline, noclone)) int f6 (struct B *p, char *w, int z) { asm
volatile ("" : : "g" (p), "g" (w), "g" (z) : "memory"); return 0; }
__attribute__ ((noinline, noclone)) void f7 (struct B *p) { asm volatile ("" :
: "g" (p) : "memory"); }
__attribute__ ((noinline, noclone)) void f8 (struct B *p) { asm volatile ("" :
: "g" (p) : "memory"); }
__attribute__ ((noinline, noclone)) void f9 (struct A *x) { asm volatile ("" :
: "g" (x) : "memory"); }
__attribute__ ((noinline, noclone)) struct A *f10 (void) { static struct A j;
asm volatile ("" : :  : "memory"); return &j; }
__attribute__ ((noinline, noclone)) struct A *f11 (void) { static struct A j;
asm volatile ("" : :  : "memory"); return &j; }
__attribute__ ((noinline, noclone)) struct A *f12 (int b) { static struct A j;
asm volatile ("" : : "g" (b) : "memory"); return &j; }
__attribute__ ((noinline, noclone)) struct A *f13 (int i) { static struct A j;
asm volatile ("" : : "g" (i) : "memory"); return &j; }
__attribute__ ((noinline, noclone)) struct A *f14 (double d) { static struct A
j; asm volatile ("" : : "g" (&d) : "memory"); return &j; }
__attribute__ ((noinline, noclone)) struct A *f15 (char *s) { static struct A
j; asm volatile ("" : : "g" (s) : "memory"); return &j; }
char *t = "0123456789abcdef";
char *u = "0123456789.+-e";

__attribute__ ((noinline, noclone)) struct A *
f1 (char *s)
{
  struct C f;
  struct A *o;
  f.c1 = s;
  f.c2 = 0;
  f.c3 = f5 ();
  o = f2 (&f);
  f8 (f.c3);
  return o;
}

static struct A *
f2 (struct C *x)
{
  int a, b, e = 0;
  struct A *f = 0, *o;
  char *g = 0;
  char h = '\0';
  int i = 0, j = 0;
  a = 0;
  b = 1;
  char c;
  do
    {
      c = x->c1[x->c2];
      switch (a)
    {
    case 0:
      if (c == ' ')
        x->c2++;
      else if (c == '/')
        {
          a = 4;
          j = x->c2++;
        }
      else
        a = b;
      break;
    case 1:
      switch (c)
        {
        case '{':
          a = 0;
          b = 15;
          f = f10 ();
          x->c2++;
          break;
        case '[':
          a = 0;
          b = 13;
          f = f11 ();
          x->c2++;
          break;
        case 'N':
        case 'n':
          a = 3;
          j = x->c2++;
          break;
        case '"':
        case '\'':
          h = c;
          f7 (x->c3);
          a = 8;
          j = ++x->c2;
          break;
        case 'T':
        case 't':
        case 'F':
        case 'f':
          a = 11;
          j = x->c2++;
          break;
        case '0' ... '9':
        case '-':
          i = 0;
          a = 12;
          j = x->c2++;
          break;
        default:
          e = 1;
          goto out;
        }
      break;
    case 2:
      goto out;
    case 3:
      if (__builtin_strncmp ("null", x->c1 + j, x->c2 - j))
        {
          e = 2;
          goto out;
        }
      if (x->c2 - j == 4)
        {
          f = 0;
          b = 2;
          a = 0;
        }
      else
        x->c2++;
      break;
    case 4:
      if (c == '*')
        a = 5;
      else if (c == '/')
        a = 6;
      else
        {
          e = 8;
          goto out;
        }
      x->c2++;
      break;
    case 5:
      if (c == '*')
        a = 7;
      x->c2++;
      break;
    case 6:
      if (c == '\n')
        a = 0;
      x->c2++;
      break;
    case 7:
      if (c == '/')
        a = 0;
      else
        a = 5;
      x->c2++;
      break;
    case 8:
      if (c == h)
        {
          f6 (x->c3, x->c1 + j, x->c2 - j);
          f = f15 (x->c3->b1);
          b = 2;
          a = 0;
        }
      else if (c == '\\')
        {
          b = 8;
          a = 9;
        }
      x->c2++;
      break;
    case 9:
      switch (c)
        {
        case '"':
        case '\\':
          f6 (x->c3, x->c1 + j, x->c2 - j - 1);
          j = x->c2++;
          a = b;
          break;
        case 'b':
        case 'n':
        case 'r':
        case 't':
          f6 (x->c3, x->c1 + j, x->c2 - j - 1);
          if (c == 'b')
        f6 (x->c3, "\b", 1);
          else if (c == 'n')
        f6 (x->c3, "\n", 1);
          else if (c == 'r')
        f6 (x->c3, "\r", 1);
          else if (c == 't')
        f6 (x->c3, "\t", 1);
          j = ++x->c2;
          a = b;
          break;
        case 'u':
          f6 (x->c3, x->c1 + j, x->c2 - j - 1);
          j = ++x->c2;
          a = 10;
          break;
        default:
          e = 7;
          goto out;
        }
      break;
    case 10:
      if (__builtin_strchr (t, c))
        {
          x->c2++;
          if (x->c2 - j == 4)
        {
          unsigned char w[3];
          unsigned int s =
            (((x->c1[j] <= '9') ? x->c1[j] - '0' : (x->c1[j] & 7) + 9) << 12)
            + (((x->c1[j + 1] <= '9') ? x->c1[j + 1] - '0' : (x->c1[j + 1] & 7)
+ 9) << 8)
            + (((x->c1[j + 2] <= '9') ? x->c1[j + 2] - '0' : (x->c1[j + 2] & 7)
+ 9) << 4)
            + ((x->c1[j + 3] <= '9') ? x->c1[j + 3] - '0' : (x->c1[j + 3] & 7)
+ 9);
          if (s < 0x80)
            {
              w[0] = s;
              f6 (x->c3, (char *) w, 1);
            }
          else if (s < 0x800)
            {
              w[0] = 0xc0 | (s >> 6);
              w[1] = 0x80 | (s & 0x3f);
              f6 (x->c3, (char *) w, 2);
            }
          else
            {
              w[0] = 0x0 | (s >> 12);
              w[1] = 0x80 | ((s >> 6) & 0x3f);
              w[2] = 0x80 | (s & 0x3f);
              f6 (x->c3, (char *) w, 3);
            }
          j = x->c2;
          a = b;
        }
        }
      else
        {
          e = 7;
          goto out;
        }
      break;
    case 11:
      if (__builtin_strncmp ("true", x->c1 + j, x->c2 - j) == 0)
        {
          if (x->c2 - j == 4)
        {
          f = f12 (1);
          b = 2;
          a = 0;
        }
          else
        x->c2++;
        }
      else if (__builtin_strncmp ("false", x->c1 + j, x->c2 - j) == 0)
        {
          if (x->c2 - j == 5)
        {
          f = f12 (0);
          b = 2;
          a = 0;
        }
          else
        x->c2++;
        }
      else
        {
          e = 3;
          goto out;
        }
      break;
    case 12:
      if (!c || !__builtin_strchr (u, c))
        {
          if (!i)
        f = f13 (0);
          else
        f = f14 (0.0);
          b = 2;
          a = 0;
        }
      else
        {
          if (c == '.' || c == 'e')
        i = 1;
          x->c2++;
        }
      break;
    case 13:
      if (c == ']')
        {
          x->c2++;
          b = 2;
          a = 0;
        }
      else
        {
          o = f2 (x);
          if (((unsigned long) o > (unsigned long) -4000L))
        {
          e = 5;
          goto out;
        }
          f3 (f, o);
          b = 14;
          a = 0;
        }
      break;
    case 14:
      if (c == ']')
        {
          x->c2++;
          b = 2;
          a = 0;
        }
      else if (c == ',')
        {
          x->c2++;
          b = 13;
          a = 0;
        }
      else
        {
          f9 (f);
          e = 5;
          goto out;
        }
      break;
    case 15:
      a = 16;
      j = x->c2;
      break;
    case 16:
      if (c == '}')
        {
          x->c2++;
          b = 2;
          a = 0;
        }
      else if (c == '"' || c == '\'')
        {
          h = c;
          f7 (x->c3);
          a = 17;
          j = ++x->c2;
        }
      else
        {
          e = 6;
          goto out;
        }
      break;
    case 17:
      if (c == h)
        {
          f6 (x->c3, x->c1 + j, x->c2 - j);
          g = __builtin_strdup (x->c3->b1);
          b = 18;
          a = 0;
        }
      else if (c == '\\')
        {
          b = 17;
          a = 9;
        }
      x->c2++;
      break;
    case 18:
      if (c == ':')
        {
          x->c2++;
          b = 19;
          a = 0;
        }
      else
        {
          e = -6;
          goto out;
        }
      break;
    case 19:
      o = f2 (x);
      if (((unsigned long) o > (unsigned long) -4000L))
        {
          e = 6;
          goto out;
        }
      f4 (f, g, o);
      __builtin_free (g);
      g = 0;
      b = 20;
      a = 0;
      break;
    case 20:
      if (c == '}')
        {
          x->c2++;
          b = 2;
          a = 0;
        }
      else if (c == ',')
        {
          x->c2++;
          b = 15;
          a = 0;
        }
      else
        {
          e = 6;
          goto out;
        }
      break;
    }
    }
  while (c);
  if (a != 2 && b != 2)
    e = 9;
out:
  __builtin_free (g);
  if (e == 0)
    return f;
  f9 (f);
  return 0;
}

int
main ()
{
  asm volatile ("" : : : "memory");
  struct A *r = f1 ("{ \"id\": null, \"blahah\": \"foobarbazbar\", \"barbar\":
{ \"barbarbarba\":"
            "\"abcdefgh\", \"ijklmnopqr\": \"stuvwxyzabcdefghijklmnopqrstuv\",
\"xyzxyz\":"
            " [ \"1\" ] } }");
  if (!r)
    __builtin_abort ();
  return 0;
}

[Bug tree-optimization/64878] [5 Regression] Miscompilation of nntpgrab

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64878

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2015-01-30
                 CC|                            |spop at gcc dot gnu.org
   Target Milestone|---                         |5.0
     Ever confirmed|0                           |1

[Bug tree-optimization/64878] [5 Regression] Miscompilation of nntpgrab

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64878

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P1

[Bug tree-optimization/64878] [5 Regression] Miscompilation of nntpgrab

[spop at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64878

--- Comment #1 from Sebastian Pop <spop at gcc dot gnu.org> ---
It fails with -O2 --param max-fsm-thread-paths=10 and does not fail with 9.
This is the thread that generates wrong code:
 Registering FSM jump thread: (102, 6) incoming edge;  (5, 128) nocopy;

[Bug tree-optimization/64878] [5 Regression] Miscompilation of nntpgrab

[spop at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64878

--- Comment #2 from Sebastian Pop <spop at gcc dot gnu.org> ---
Jump threading is called twice as two separate passes, the "miscompiled" jump
thread during the first invocation is:
 Registering FSM jump thread: (10, 114) incoming edge;  (4, 93) nocopy;

The "miscompiled" jump thread for the second invocation of dom is:

 Registering FSM jump thread: (102, 6) incoming edge;  (5, 128) nocopy;

[Bug tree-optimization/64878] [5 Regression] Miscompilation of nntpgrab

[spop at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64878

--- Comment #3 from Sebastian Pop <spop at gcc dot gnu.org> ---
-fdbg-cnt=registered_jump_thread:44 passes
-fdbg-cnt=registered_jump_thread:45 fails

So this is the jump thread that produces the wrong code:
 Registering FSM jump thread: (10, 114) incoming edge;  (4, 93) nocopy

[Bug tree-optimization/64878] [5 Regression] Miscompilation of nntpgrab

[spop at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64878

--- Comment #4 from Sebastian Pop <spop at gcc dot gnu.org> ---
The problem is in the recursion step of
fsm_find_control_statement_thread_paths:


  for (i = 0; i < gimple_phi_num_args (phi); i++)
    {
      tree arg = gimple_phi_arg_def (phi, i);
      basic_block bbi = gimple_phi_arg_edge (phi, i)->src;
[...]
      if (TREE_CODE (arg) == SSA_NAME)
    {
      vec_safe_push (path, bbi);
      /* Recursively follow SSA_NAMEs looking for a constant definition.  */
      fsm_find_control_statement_thread_paths (arg, visited_phis, path);
      path->pop ();
      continue;
    }

We are not supposed to register a jump-thread following only one of the PHI
arguments, as the other arguments may resolve into a non-constant or a
different constant.

In the current case, we have 

      c = x->c1[x->c2];
      switch (a)
    {
    case 0:
      if (c == ' ')
        x->c2++;
      else if (c == '/')
        {
          a = 4;   // here is the first argument of the phi node
          j = x->c2++;
        }
      else
        a = b;    // recursive call will follow b and resolve into 15

         // here the phi node looks like
         // a0 = phi (4, b)

      break;
    case 1:
      switch (c)
        {
        case '{':
          a = 0;
          b = 15;
          f = f10 ();
          x->c2++;
          break;

[Bug tree-optimization/64878] [5 Regression] Miscompilation of nntpgrab

[spop at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64878

--- Comment #5 from Sebastian Pop <spop at gcc dot gnu.org> ---
Created attachment 34665
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=34665&action=edit
fix

The problem is that we jump thread twice across the loop latch:
first, from

        case '{':
          a = 0;
          b = 15;
          f = f10 ();
          x->c2++;
          break;
through the loop latch to: 

    case 0:
      if (c == ' ')
        x->c2++;
      else if (c == '/')
        {
          a = 4;
          j = x->c2++;
        }
      else
        a = b;

and second, from "a = b;" again across the loop latch to case 15.
Attached patch fixes the wrong code and passes make check.

[Bug tree-optimization/64878] [5 Regression] Miscompilation of nntpgrab

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64878

--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(In reply to Sebastian Pop from comment #5)
> Created attachment 34665 [details]
> fix

Thanks for working on this.  s/accross/across/.  Please mail it to gcc-patches
once you test it.

[Bug tree-optimization/64878] [5 Regression] Miscompilation of nntpgrab

[spop at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64878

--- Comment #7 from Sebastian Pop <spop at gcc dot gnu.org> ---
Author: spop
Date: Fri Feb  6 21:08:13 2015
New Revision: 220491

URL: https://gcc.gnu.org/viewcvs?rev=220491&root=gcc&view=rev
Log:
PR 64878: do not jump thread across more than one back-edge

2015-02-04  Sebastian Pop  <s.pop@samsung.com>
        Brian Rzycki  <b.rzycki@samsung.com>

    PR tree-optimization/64878
    * tree-ssa-threadedge.c: Include tree-ssa-loop.h.
    (fsm_find_control_statement_thread_paths): Add parameter seen_loop_phi.
    Stop recursion at loop phi nodes after having visited a loop phi node.

    * testsuite/gcc.dg/tree-ssa/ssa-dom-thread-8.c: New.

Added:
    trunk/gcc/testsuite/gcc.dg/tree-ssa/ssa-dom-thread-8.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/tree-ssa-threadedge.c

[Bug tree-optimization/64878] [5 Regression] Miscompilation of nntpgrab

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64878

Jakub Jelinek <jakub at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
         Resolution|---                         |FIXED

--- Comment #8 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Fixed, thanks.

[Bug tree-optimization/64878] [5 Regression] Miscompilation of nntpgrab

[yroux at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64878

--- Comment #9 from Yvan Roux <yroux at gcc dot gnu.org> ---
Author: yroux
Date: Thu Mar  5 14:28:05 2015
New Revision: 221216

URL: https://gcc.gnu.org/viewcvs?rev=221216&root=gcc&view=rev
Log:
gcc/
2015-03-05  Yvan Roux  <yvan.roux@linaro.org>

    Backport from trunk r212011, r214942, r214957, r215012, r215016, r218115,
    r218733, r218746, r220491.
    2015-02-06  Sebastian Pop  <s.pop@samsung.com>
            Brian Rzycki  <b.rzycki@samsung.com>

    PR tree-optimization/64878
    * tree-ssa-threadedge.c: Include tree-ssa-loop.h.
    (fsm_find_control_statement_thread_paths): Add parameter seen_loop_phi.
    Stop recursion at loop phi nodes after having visited a loop phi node.

    2014-12-15  Richard Biener  <rguenther@suse.de>

    PR middle-end/64246
    * cfgloop.c (mark_loop_for_removal): Make safe against multiple
    invocations on the same loop.

    2014-12-15  Richard Biener  <rguenther@suse.de>

    PR tree-optimization/64284
    * tree-ssa-threadupdate.c (duplicate_seme_region): Mark
    the loop for removal if we copied the loop header.

    2014-11-27  Richard Biener  <rguenther@suse.de>

    PR tree-optimization/64083
    * tree-ssa-threadupdate.c (thread_through_all_blocks): Do not
    forcibly mark loop for removal the wrong way.

    2014-09-08  Richard Biener  <rguenther@suse.de>

    PR ipa/63196
    * tree-inline.c (copy_loops): The source loop header should
    always be non-NULL.
    (tree_function_versioning): If loops need fixup after removing
    unreachable blocks fix them.
    * omp-low.c (simd_clone_adjust): Do not add incr block to
    loop under construction.

    2014-09-08  Richard Biener  <rguenther@suse.de>

    PR bootstrap/63204
    * cfgloop.c (mark_loop_for_removal): Track former header
    unconditionally.
    * cfgloop.h (struct loop): Add former_header member unconditionally.
    * loop-init.c (fix_loop_structure): Enable bogus loop removal
    diagnostic unconditionally.

    2014-09-05  Richard Biener  <rguenther@suse.de>

    * cfgloop.c (mark_loop_for_removal): Record former header
    when ENABLE_CHECKING.
    * cfgloop.h (strut loop): Add former_header member when
    ENABLE_CHECKING.
    * loop-init.c (fix_loop_structure): Sanity check loops
    marked for removal if they re-appeared.

    2014-09-05  Richard Biener  <rguenther@suse.de>

    * cfgloop.c (mark_loop_for_removal): New function.
    * cfgloop.h (mark_loop_for_removal): Declare.
    * cfghooks.c (delete_basic_block): Use mark_loop_for_removal.
    (merge_blocks): Likewise.
    (duplicate_block): Likewise.
    * except.c (sjlj_emit_dispatch_table): Likewise.
    * tree-eh.c (cleanup_empty_eh_merge_phis): Likewise.
    * tree-ssa-threadupdate.c (ssa_redirect_edges): Likewise.
    (thread_through_loop_header): Likewise.

    2014-06-26  Richard Biener  <rguenther@suse.de>

    PR tree-optimization/61607
    * tree-ssa-threadupdate.c (ssa_redirect_edges): Cancel the
    loop if we redirected its latch edge.
    (thread_block_1): Do not cancel loops prematurely.

gcc/testsuite/
2015-03-05  Yvan Roux  <yvan.roux@linaro.org>

    Backport from trunk r218115, r218733, r218746, r220491.
    2015-02-06  Sebastian Pop  <s.pop@samsung.com>
            Brian Rzycki  <b.rzycki@samsung.com>

    PR tree-optimization/64878
    * testsuite/gcc.dg/tree-ssa/ssa-dom-thread-8.c: New.

    2014-12-15  Richard Biener  <rguenther@suse.de>

    PR middle-end/64246
    * gnat.dg/opt46.adb: New testcase.
    * gnat.dg/opt46.ads: Likewise.
    * gnat.dg/opt46_pkg.adb: Likewise.
    * gnat.dg/opt46_pkg.ads: Likewise.

    2014-12-15  Richard Biener  <rguenther@suse.de>

    PR tree-optimization/64284
    * gcc.dg/torture/pr64284.c: New testcase.

    2014-11-27  Richard Biener  <rguenther@suse.de>

    PR tree-optimization/64083
    * gcc.dg/torture/pr64083.c: New testcase.


Added:
    branches/linaro/gcc-4_9-branch/gcc/testsuite/gcc.dg/torture/pr64083.c
    branches/linaro/gcc-4_9-branch/gcc/testsuite/gcc.dg/torture/pr64284.c
   
branches/linaro/gcc-4_9-branch/gcc/testsuite/gcc.dg/tree-ssa/ssa-dom-thread-8.c
    branches/linaro/gcc-4_9-branch/gcc/testsuite/gnat.dg/opt46.adb
    branches/linaro/gcc-4_9-branch/gcc/testsuite/gnat.dg/opt46.ads
    branches/linaro/gcc-4_9-branch/gcc/testsuite/gnat.dg/opt46_pkg.adb
    branches/linaro/gcc-4_9-branch/gcc/testsuite/gnat.dg/opt46_pkg.ads
Modified:
    branches/linaro/gcc-4_9-branch/gcc/ChangeLog.linaro
    branches/linaro/gcc-4_9-branch/gcc/cfghooks.c
    branches/linaro/gcc-4_9-branch/gcc/cfgloop.c
    branches/linaro/gcc-4_9-branch/gcc/cfgloop.h
    branches/linaro/gcc-4_9-branch/gcc/except.c
    branches/linaro/gcc-4_9-branch/gcc/loop-init.c
    branches/linaro/gcc-4_9-branch/gcc/omp-low.c
    branches/linaro/gcc-4_9-branch/gcc/testsuite/ChangeLog.linaro
    branches/linaro/gcc-4_9-branch/gcc/tree-eh.c
    branches/linaro/gcc-4_9-branch/gcc/tree-inline.c
    branches/linaro/gcc-4_9-branch/gcc/tree-ssa-threadedge.c
    branches/linaro/gcc-4_9-branch/gcc/tree-ssa-threadupdate.c