[PATCH] Fix PR79390 (partly)

[Richard Biener]

This avoids another case of path splitting which gets in the way
of RTL if conversion.  With this patch -O3 performance gets back
to GCC 6 levels (with -Ofast we still regress as RTL if conversion
doesn't catch the case).

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

Richard.

2017-04-12  Richard Biener  <rguent...@suse.de>

        PR tree-optimization/79390
        * gimple-ssa-split-paths.c (is_feasible_trace): Restrict
        threading case even more.

Index: gcc/gimple-ssa-split-paths.c
===================================================================
--- gcc/gimple-ssa-split-paths.c        (revision 246803)
+++ gcc/gimple-ssa-split-paths.c        (working copy)
@@ -249,13 +249,17 @@ is_feasible_trace (basic_block bb)
                  imm_use_iterator iter2;
                  FOR_EACH_IMM_USE_FAST (use2_p, iter2, gimple_phi_result 
(stmt))
                    {
-                     if (is_gimple_debug (USE_STMT (use2_p)))
+                     gimple *use_stmt = USE_STMT (use2_p);
+                     if (is_gimple_debug (use_stmt))
                        continue;
-                     basic_block use_bb = gimple_bb (USE_STMT (use2_p));
+                     basic_block use_bb = gimple_bb (use_stmt);
                      if (use_bb != bb
                          && dominated_by_p (CDI_DOMINATORS, bb, use_bb))
                        {
-                         found_useful_phi = true;
+                         if (gcond *cond = dyn_cast <gcond *> (use_stmt))
+                           if (gimple_cond_code (cond) == EQ_EXPR
+                               || gimple_cond_code (cond) == NE_EXPR)
+                             found_useful_phi = true;
                          break;
                        }
                    }