[PATCH, PR69067] Remove assert in get_def_bb_for_const

[Tom de Vries <Tom_deVries at mentor dot com>]

Hi,

this patch fixes graphite PR69067, a 6/7 regression.


I.

Consider the following test-case, compiled with -O1 -floop-nest-optimize 
-flto:
...
int a1, c1, cr, kt;
int aa[2];

int
ce (void)
{
  while (a1 < 1) {
    int g8;
    for (g8 = 0; g8 < 3; ++g8)
      if (c1 != 0)
        cr = aa[a1 * 2] = kt;
    for (c1 = 0; c1 < 2; ++c1)
      aa[c1] = cr;
    ++a1;
  }
  return 0;
}

int
main (void)
{
  return ce (aa);
}
...

At graphite0, there's a loop with header bb4, which conditionally 
executes bb 5:
...
  <bb 3>:

  <bb 4>:
  # g8_39 = PHI <0(13), g8_19(3)>
  # cr_lsm.1_4 = PHI <cr_lsm.1_21(13), cr_lsm.1_33(3)>
  # cr_lsm.2_22 = PHI <cr_lsm.2_23(13), cr_lsm.2_11(3)>
  if (c1_lsm.3_35 != 0)
    goto <bb 5>;
  else
    goto <bb 6>;

  <bb 5>:
  aa[_3] = 0;

  <bb 6>:
  # cr_lsm.1_33 = PHI <cr_lsm.1_4(4), 0(5)>
  # cr_lsm.2_11 = PHI <cr_lsm.2_22(4), 1(5)>
  g8_19 = g8_39 + 1;
  if (g8_19 <= 2)
    goto <bb 3>;
  else
    goto <bb 7>;
...


II.

The graphite transformation moves the condition '(P_35 <= -1 || P_35 >= 
1)' out of the loop:
...
[scheduler] original ast:
{
  for (int c0 = 0; c0 <= 2; c0 += 1) {
    S_4(c0);
    if (P_35 <= -1 || P_35 >= 1)
      S_5(c0);
    S_6(c0);
  }
  S_7();
  for (int c0 = 0; c0 <= 1; c0 += 1)
    S_8(c0);
}

[scheduler] AST generated by isl:
{
  if (P_35 <= -1) {
    for (int c0 = 0; c0 <= 2; c0 += 1)
      S_5(c0);
  } else if (P_35 >= 1)
    for (int c0 = 0; c0 <= 2; c0 += 1)
      S_5(c0);
  for (int c0 = 0; c0 <= 2; c0 += 1) {
    S_4(c0);
    S_6(c0);
  }
  S_7();
  for (int c0 = 0; c0 <= 1; c0 += 1)
    S_8(c0);
}
...

When instantiating the ast back to gimple, we run into an assert:
...
pr-graphite-4.c: In function âceâ:
pr-graphite-4.c:5:1: internal compiler error: in get_def_bb_for_const, 
at graphite-isl-ast-to-gimple.c:1795
 ce()
 ^
...


III.

What happens is the following: in copy_cond_phi_args we try to copy the 
arguments of phi in bb6 to the arguments of new_phi in bb 46
...
(gdb) call debug_gimple_stmt (phi)
cr_lsm.1_33 = PHI <cr_lsm.1_4(4), 0(5)>
(gdb) call debug_gimple_stmt (new_phi)
cr_lsm.1_62 = PHI <(28), (47)>
...

While handling the '0' phi argument in add_phi_arg_for_new_expr we 
trigger this bit of code and call get_def_bb_for_const with bb.index == 
46 and old_bb.index == 5:
...
  /* If the corresponding def_bb could not be found the entry will
     be NULL.  */
  if (TREE_CODE (old_phi_args[i]) == INTEGER_CST)
    def_pred[i]
      = get_def_bb_for_const (new_bb,
                              gimple_phi_arg_edge (phi, i)->src);
...

Neither of the two copies of bb 5 dominates bb 46, so we run into the 
assert at the end:
...
/* Returns a basic block that could correspond to where a constant was
  defined in the original code.  In the original code OLD_BB had the
  definition, we need to find which basic block out of the copies of
  old_bb, in the new region, should a definition correspond to if it
  has to reach BB.  */

basic_block translate_isl_ast_to_gimple::
get_def_bb_for_const (basic_block bb, basic_block old_bb) const
{
  vec <basic_block> *bbs = region->copied_bb_map->get (old_bb);

  if (!bbs || bbs->is_empty ())
    return NULL;

  if (1 == bbs->length ())
    return (*bbs)[0];

  int i;
  basic_block b1 = NULL, b2;
  FOR_EACH_VEC_ELT (*bbs, i, b2)
    {
      if (b2 == bb)
        return bb;

      /* BB and B2 are in two unrelated if-clauses.  */
      if (!dominated_by_p (CDI_DOMINATORS, bb, b2))
        continue;

      /* Compute the nearest dominator.  */
      if (!b1 || dominated_by_p (CDI_DOMINATORS, b2, b1))
        b1 = b2;
    }

  gcc_assert (b1);
  return b1;
}
...


IV.

Attached patch fixes this by removing the assert.

Bootstrapped and reg-tested on x86_64.

OK for trunk, 6-branch?

Thanks,
- Tom

Remove assert in get_def_bb_for_const

2016-05-29  Tom de Vries  <tom@codesourcery.com>

	PR tree-optimization/69067
	* graphite-isl-ast-to-gimple.c (get_def_bb_for_const): Remove assert.

	* gcc.dg/graphite/pr69067.c: New test.

---
 gcc/graphite-isl-ast-to-gimple.c        |  1 -
 gcc/testsuite/gcc.dg/graphite/pr69067.c | 28 ++++++++++++++++++++++++++++
 2 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/gcc/graphite-isl-ast-to-gimple.c b/gcc/graphite-isl-ast-to-gimple.c
index 049a4c5..ff1d91f 100644
--- a/gcc/graphite-isl-ast-to-gimple.c
+++ b/gcc/graphite-isl-ast-to-gimple.c
@@ -1792,7 +1792,6 @@ get_def_bb_for_const (basic_block bb, basic_block old_bb) const
 	b1 = b2;
     }
 
-  gcc_assert (b1);
   return b1;
 }
 
diff --git a/gcc/testsuite/gcc.dg/graphite/pr69067.c b/gcc/testsuite/gcc.dg/graphite/pr69067.c
new file mode 100644
index 0000000..d767381d
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/graphite/pr69067.c
@@ -0,0 +1,28 @@
+/* { dg-do link } */
+/* { dg-options " -O1 -floop-nest-optimize" } */
+/* { dg-additional-options "-flto" { target lto } } */
+
+int a1, c1, cr, kt;
+int aa[2];
+
+int
+ce (void)
+{
+  while (a1 < 1)
+    {
+      int g8;
+      for (g8 = 0; g8 < 3; ++g8)
+	if (c1 != 0)
+	  cr = aa[a1 * 2] = kt;
+      for (c1 = 0; c1 < 2; ++c1)
+	aa[c1] = cr;
+      ++a1;
+    }
+  return 0;
+}
+
+int
+main (void)
+{
+  return ce (aa);
+}