[PATCH, PR69068] Handle 3-arg phi in copy_bb_and_scalar_dependences

[Tom de Vries]

Hi,

this patch fixes graphite PR69068, a 6/7 regression.

I.

Consider this test-case:
...
int qo;
int zh[2];

void
td (void)
{
  int ly, en;
  for (ly = 0; ly < 2; ++ly)
    for (en = 0; en < 2; ++en)
      zh[en] = ((qo == 0) || (((qo * 2) != 0))) ? 1 : -1;
}
...

When compiling with -O1 -fgraphite-identity, we run into an assert in 
bb_contains_loop_phi_nodes:
...
pr-graphite.c: In function ‘td’:
pr-graphite.c:5:1: internal compiler error: in 
bb_contains_loop_phi_nodes, at graphite-isl-ast-to-gimple.c:1078
td(void)
^~
...


II.

At graphite0, we have a 3 argument phi in bb 7:
...
td ()
{
  int en;
  int ly;
  int qo.1_1;
  int _3;
  int iftmp.0_6;

  <bb 2>:
  qo.1_1 = qo;
  _3 = qo.1_1 * 2;
  goto <bb 10>;

  <bb 3>:

  <bb 4>:
  # en_19 = PHI <0(10), en_12(3)>
  if (qo.1_1 == 0)
    goto <bb 7>;
  else
    goto <bb 5>;

  <bb 5>:
  if (_3 != 0)
    goto <bb 6>;
  else
    goto <bb 7>;

  <bb 6>:

  <bb 7>:
  # iftmp.0_6 = PHI <1(6), -1(5), 1(4)>
  zh[en_19] = iftmp.0_6;
  en_12 = en_19 + 1;
  if (en_12 <= 1)
    goto <bb 3>;
  else
    goto <bb 8>;

  <bb 8>:
  ly_13 = ly_18 + 1;
  if (ly_13 <= 1)
    goto <bb 9>;
  else
    goto <bb 11>;

  <bb 9>:

  <bb 10>:
  # ly_18 = PHI <ly_13(9), 0(2)>
  goto <bb 4>;

  <bb 11>:
  return;

}
...

When instantiating the gimple from the graphite ast, we arrive at 
copy_bb_and_scalar_dependences with bb.index == 7, where we execute:
...
      if (num_phis > 0 && bb_contains_loop_phi_nodes (bb))
        {
...

Subsequently we run into this assert, because
EDGE_COUNT (bb->preds) == 3:
...
/* Return true when BB contains loop phi nodes.  A loop phi node is the
   loop header containing phi nodes which has one init-edge and one
   back-edge.  */

static bool
bb_contains_loop_phi_nodes (basic_block bb)
{
  gcc_assert (EDGE_COUNT (bb->preds) <= 2);
...


III.

This patch fixes the assert conservatively by aborting graphite code 
generation when encountering a phi with more than two arguments in 
copy_bb_and_scalar_dependences.

Bootstrapped and reg-tested on x86_64.

OK for trunk, 6 branch?

Thanks,
- Tom
Handle 3-arg phi in copy_bb_and_scalar_dependences

2016-05-30  Tom de Vries  <t...@codesourcery.com>

	PR tree-optimization/69068
	* graphite-isl-ast-to-gimple.c (copy_bb_and_scalar_dependences): Handle
	phis with more than two args.

	* gcc.dg/graphite/pr69068.c: New test.

---
 gcc/graphite-isl-ast-to-gimple.c        |  7 +++++++
 gcc/testsuite/gcc.dg/graphite/pr69068.c | 14 ++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/gcc/graphite-isl-ast-to-gimple.c b/gcc/graphite-isl-ast-to-gimple.c
index ff1d91f..c176db0 100644
--- a/gcc/graphite-isl-ast-to-gimple.c
+++ b/gcc/graphite-isl-ast-to-gimple.c
@@ -2725,6 +2725,13 @@ copy_bb_and_scalar_dependences (basic_block bb, edge next_e, vec<tree> iv_map)
     }
   else
     {
+      if (num_phis > 0
+	  && EDGE_COUNT (bb->preds) > 2)
+	{
+	  codegen_error = true;
+	  return NULL;
+	}
+
       new_bb = split_edge (next_e);
       if (num_phis > 0 && bb_contains_loop_phi_nodes (bb))
 	{
diff --git a/gcc/testsuite/gcc.dg/graphite/pr69068.c b/gcc/testsuite/gcc.dg/graphite/pr69068.c
new file mode 100644
index 0000000..0abea06
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/graphite/pr69068.c
@@ -0,0 +1,14 @@
+/* { dg-do compile } */
+/* { dg-options "-O1 -fgraphite-identity" } */
+
+int qo;
+int zh[2];
+
+void
+td (void)
+{
+  int ly, en;
+  for (ly = 0; ly < 2; ++ly)
+    for (en = 0; en < 2; ++en)
+      zh[en] = ((qo == 0) || (((qo * 2) != 0))) ? 1 : -1;
+}