[PATCH] Fix PR79622

[Richard Biener]

The following patch fixes the other known wrong-code bug in GRAPHITE
which shows we're mishandling PHIs in not properly considering the
edge copies they represent as living outside of the black-box we're
analyzing.

Bootstrapped and tested on x86_64-unknown-linux-gnu, applied to trunk.

Note the testcase still fails with ISL 0.16.1 but passes with 0.18
for me.  I'll update the version in download_prerequesites to 0.18.

Richard.

2017-09-18  Richard Biener  <rguent...@suse.de>

        PR tree-optimization/79622
        * graphite-scop-detection.c (build_cross_bb_scalars_def): Properly
        handle PHIs.
        (build_cross_bb_scalars_use): Likewise.

        * gcc.dg/graphite/pr79622.c: New testcase.

Index: gcc/graphite-scop-detection.c
===================================================================
--- gcc/graphite-scop-detection.c       (revision 252806)
+++ gcc/graphite-scop-detection.c       (working copy)
@@ -1744,7 +1744,9 @@ build_cross_bb_scalars_def (scop_p scop,
   gimple *use_stmt;
   imm_use_iterator imm_iter;
   FOR_EACH_IMM_USE_STMT (use_stmt, imm_iter, def)
-    if (def_bb != gimple_bb (use_stmt) && !is_gimple_debug (use_stmt))
+    if ((def_bb != gimple_bb (use_stmt) && !is_gimple_debug (use_stmt))
+       /* PHIs have their effect at "BBs" on the edges.  See PR79622.  */
+       || gimple_code (SSA_NAME_DEF_STMT (def)) == GIMPLE_PHI)
       {
        writes->safe_push (def);
        DEBUG_PRINT (dp << "Adding scalar write: ";
@@ -1758,7 +1760,8 @@ build_cross_bb_scalars_def (scop_p scop,
       }
 }
 
-/* Record DEF if it is used in other bbs different than DEF_BB in the SCOP.  */
+/* Record USE if it is defined in other bbs different than USE_STMT
+   in the SCOP.  */
 
 static void
 build_cross_bb_scalars_use (scop_p scop, tree use, gimple *use_stmt,
@@ -1774,7 +1777,9 @@ build_cross_bb_scalars_use (scop_p scop,
     return;
 
   gimple *def_stmt = SSA_NAME_DEF_STMT (use);
-  if (gimple_bb (def_stmt) != gimple_bb (use_stmt))
+  if (gimple_bb (def_stmt) != gimple_bb (use_stmt)
+      /* PHIs have their effect at "BBs" on the edges.  See PR79622.  */
+      || gimple_code (def_stmt) == GIMPLE_PHI)
     {
       DEBUG_PRINT (dp << "Adding scalar read: ";
                   print_generic_expr (dump_file, use);
Index: gcc/testsuite/gcc.dg/graphite/pr79622.c
===================================================================
--- gcc/testsuite/gcc.dg/graphite/pr79622.c     (nonexistent)
+++ gcc/testsuite/gcc.dg/graphite/pr79622.c     (working copy)
@@ -0,0 +1,26 @@
+/* { dg-do run } */
+/* { dg-options "-O2 -floop-nest-optimize" } */
+
+int bf;
+
+int
+main (void)
+{
+  int dc[5];
+
+  for (bf = 0; bf < 2; ++bf)
+    {
+      int l9, g5 = -1;
+
+      for (l9 = 0; l9 < 5; ++l9)
+       {
+         dc[l9] = g5;
+         g5 = (dc[l9] > 0);
+       }
+    }
+
+  if (dc[0] != -1)
+    __builtin_abort ();
+
+  return 0;
+}