[PATCH] [PR tree-optimization/69196] Consider two anonymous SSA_NAMEs unassociated

[Jeff Law]

As pointed out by Richi, the code did not precisely match the comment in 
the case of two anonymous SSA_NAMEs.

In that case we don't have enough information to determine if the names 
are associated.  Until we do something like build partitions (similar to 
what's done in tree-ssa-coalesce), it seems best to consider two 
anonymous SSA_NAMEs to be unassociated and count the PHI against the 
statement count for threading.

Bootstrapped and regression tested on x86-64.  Installed on the trunk.

Jeff
commit 2ef58c4014fc23573d8ff10e50381c6cbdcba6e6
Author: law <law@138bc75d-0d04-0410-961f-82ee72b054a4>
Date:   Sat Mar 5 05:10:58 2016 +0000

        PR tree-optimization/69196
        * tree-ssa-threadbackward.c (fsm_find_control_statement_thread_paths):
        If the both SSA_NAMEs are anonymous, then consider them unassociated
        and include the PHI in the statement count.
    
    git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@233999 
138bc75d-0d04-0410-961f-82ee72b054a4

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 5c23836..09a2714 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,10 @@
+2016-03-04  Jeff Law  <l...@redhat.com>
+
+       PR tree-optimization/69196
+       * tree-ssa-threadbackward.c (fsm_find_control_statement_thread_paths):
+       If the both SSA_NAMEs are anonymous, then consider them unassociated
+       and include the PHI in the statement count.
+
 2016-03-05  Tom de Vries  <t...@codesourcery.com>
 
        * omp-low.c (check_omp_nesting_restrictions): Check for non-oacc
diff --git a/gcc/tree-ssa-threadbackward.c b/gcc/tree-ssa-threadbackward.c
index 747296b..6f1b757 100644
--- a/gcc/tree-ssa-threadbackward.c
+++ b/gcc/tree-ssa-threadbackward.c
@@ -311,7 +311,11 @@ fsm_find_control_statement_thread_paths (tree name,
                          gphi *phi = gsip.phi ();
                          tree dst = gimple_phi_result (phi);
 
-                         if (SSA_NAME_VAR (dst) != SSA_NAME_VAR (name)
+                         /* Note that if both NAME and DST are anonymous
+                            SSA_NAMEs, then we do not have enough information
+                            to consider them associated.  */
+                         if ((SSA_NAME_VAR (dst) != SSA_NAME_VAR (name)
+                              || !SSA_NAME_VAR (dst))
                              && !virtual_operand_p (dst))
                            ++n_insns;
                        }