[PATCH] tree-optimization/112767 - spurious diagnostic after sccp/loop-split swap

[Richard Biener]

We are diagnosing an unreachable loop which we only manage to elide
after the copyprop pass after sccp which leaves the code open for
diagnosing by the intermittent ivcanon pass.  The following makes sure
to clean things up a bit earlier, propagating constant final values
to uses immediately.

Bootstrapped and tested on x86_64-unknown-linux-gnu, pushed.

        PR tree-optimization/112767
        * tree-scalar-evolution.cc (final_value_replacement_loop):
        Propagate constants to immediate uses immediately.

        * gcc.dg/tree-ssa/pr112767.c: New testcase.
        * gcc.dg/graphite/pr83255.c: Disable SCCP.
---
 gcc/testsuite/gcc.dg/graphite/pr83255.c  |  2 +-
 gcc/testsuite/gcc.dg/tree-ssa/pr112767.c | 18 ++++++++++++++++++
 gcc/tree-scalar-evolution.cc             | 11 ++++++++++-
 3 files changed, 29 insertions(+), 2 deletions(-)
 create mode 100644 gcc/testsuite/gcc.dg/tree-ssa/pr112767.c

diff --git a/gcc/testsuite/gcc.dg/graphite/pr83255.c 
b/gcc/testsuite/gcc.dg/graphite/pr83255.c
index cb376fa61be..07532632787 100644
--- a/gcc/testsuite/gcc.dg/graphite/pr83255.c
+++ b/gcc/testsuite/gcc.dg/graphite/pr83255.c
@@ -1,5 +1,5 @@
 /* { dg-do run } */
-/* { dg-options "-O -floop-nest-optimize -fdump-tree-graphite-details" } */
+/* { dg-options "-O -floop-nest-optimize -fno-tree-scev-cprop 
-fdump-tree-graphite-details" } */
 
 int rx, in;
 
diff --git a/gcc/testsuite/gcc.dg/tree-ssa/pr112767.c 
b/gcc/testsuite/gcc.dg/tree-ssa/pr112767.c
new file mode 100644
index 00000000000..3f9bc061ee1
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/tree-ssa/pr112767.c
@@ -0,0 +1,18 @@
+/* { dg-do compile } */
+/* { dg-options "-O3" } */
+
+double reg_dict[32];
+
+void foo(int);
+
+void initialize()
+{
+  int i=8;
+  for (int phi=0; phi<8; ++phi) {
+    reg_dict[i]=0; /* { dg-bogus "undefined behavior" } */
+    int sn = 0;
+    if (i < 16) sn = 20;
+    foo(sn);
+    ++i;
+  }
+}
diff --git a/gcc/tree-scalar-evolution.cc b/gcc/tree-scalar-evolution.cc
index f61277c32df..065bcd0743d 100644
--- a/gcc/tree-scalar-evolution.cc
+++ b/gcc/tree-scalar-evolution.cc
@@ -3841,11 +3841,20 @@ final_value_replacement_loop (class loop *loop)
          print_gimple_stmt (dump_file, phi, 0);
          fprintf (dump_file, " with expr: ");
          print_generic_expr (dump_file, def);
+         fprintf (dump_file, "\n");
        }
       any = true;
       def = unshare_expr (def);
       remove_phi_node (&psi, false);
 
+      /* Propagate constants immediately.  */
+      if (CONSTANT_CLASS_P (def))
+       {
+         replace_uses_by (rslt, def);
+         release_ssa_name (rslt);
+         continue;
+       }
+
       /* Create the replacement statements.  */
       gimple_seq stmts;
       def = force_gimple_operand (def, &stmts, false, NULL_TREE);
@@ -3877,7 +3886,7 @@ final_value_replacement_loop (class loop *loop)
       gsi_insert_seq_before (&gsi, stmts, GSI_SAME_STMT);
       if (dump_file)
        {
-         fprintf (dump_file, "\n final stmt:\n  ");
+         fprintf (dump_file, " final stmt:\n  ");
          print_gimple_stmt (dump_file, SSA_NAME_DEF_STMT (rslt), 0);
          fprintf (dump_file, "\n");
        }
-- 
2.35.3