[PATCH] Avoid compile-time overhead of GIMPLE FE in CFG construction

[Richard Biener]

$subject

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

Richard.

2016-11-29  Richard Biener  <rguent...@suse.de>

        * tree-cfg.c (lower_phi_internal_fn): Do not look for further
        PHIs after a regular stmt.
        (stmt_starts_bb_p): PHIs not preceeded by a PHI or a label
        start a new BB.

Index: gcc/tree-cfg.c
===================================================================
--- gcc/tree-cfg.c      (revision 242953)
+++ gcc/tree-cfg.c      (working copy)
@@ -361,14 +361,11 @@ lower_phi_internal_fn ()
   /* After edge creation, handle __PHI function from GIMPLE FE.  */
   FOR_EACH_BB_FN (bb, cfun)
     {
-      for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi);)
+      for (gsi = gsi_after_labels (bb); !gsi_end_p (gsi);)
        {
          stmt = gsi_stmt (gsi);
          if (! gimple_call_internal_p (stmt, IFN_PHI))
-           {
-             gsi_next (&gsi);
-             continue;
-           }
+           break;
 
          lhs = gimple_call_lhs (stmt);
          phi_node = create_phi_node (lhs, bb);
@@ -2604,11 +2601,21 @@ stmt_starts_bb_p (gimple *stmt, gimple *
       else
        return true;
     }
-  else if (gimple_code (stmt) == GIMPLE_CALL
-          && gimple_call_flags (stmt) & ECF_RETURNS_TWICE)
-    /* setjmp acts similar to a nonlocal GOTO target and thus should
-       start a new block.  */
-    return true;
+  else if (gimple_code (stmt) == GIMPLE_CALL)
+    {
+      if (gimple_call_flags (stmt) & ECF_RETURNS_TWICE)
+       /* setjmp acts similar to a nonlocal GOTO target and thus should
+          start a new block.  */
+       return true;
+      if (gimple_call_internal_p (stmt, IFN_PHI)
+         && prev_stmt
+         && gimple_code (prev_stmt) != GIMPLE_LABEL
+         && (gimple_code (prev_stmt) != GIMPLE_CALL
+             || ! gimple_call_internal_p (prev_stmt, IFN_PHI)))
+       /* PHI nodes start a new block unless preceeded by a label
+          or another PHI.  */
+       return true;
+    }
 
   return false;
 }