GCC Middle and Back End API Reference
tree-ssa-loop-unswitch.c File Reference


static struct looptree_unswitch_loop (struct loop *, basic_block, tree)
static bool tree_unswitch_single_loop (struct loop *, int)
static tree tree_may_unswitch_on (basic_block, struct loop *)
unsigned int tree_ssa_unswitch_loops ()
static tree tree_may_unswitch_on ()
static tree simplify_using_entry_checks ()
static bool tree_unswitch_single_loop ()
static unsigned int tree_ssa_loop_unswitch ()
static bool gate_tree_ssa_loop_unswitch ()
gimple_opt_passmake_pass_tree_unswitch ()

Function Documentation

static bool gate_tree_ssa_loop_unswitch ( )
gimple_opt_pass* make_pass_tree_unswitch ( )
static tree simplify_using_entry_checks ( )
   Simplifies COND using checks in front of the entry of the LOOP.  Just very
   simplish (sufficient to prevent us from duplicating loop in unswitching

Referenced by tree_unswitch_single_loop().

static tree tree_may_unswitch_on ( basic_block  ,
struct loop  
static tree tree_may_unswitch_on ( )
   Checks whether we can unswitch LOOP on condition at end of BB -- one of its
   basic blocks (for what it means see comments below).  
     BB must end in a simple conditional jump.  
     To keep the things simple, we do not directly remove the conditions,
     but just replace tests with 0 != 0 resp. 1 != 0.  Prevent the infinite
     loop where we would unswitch again on such a condition.  
     Condition must be invariant.  
static unsigned int tree_ssa_loop_unswitch ( )
   Loop unswitching pass.  
unsigned int tree_ssa_unswitch_loops ( )
   Main entry point.  Perform loop unswitching on all suitable loops.  
     Go through inner loops (only original ones).  
         Do not unswitch in cold regions. 
         The loop should not be too large, to limit code growth. 
         If the loop is not expected to iterate, there is no need
         for unswitching.  

References dump_file, dump_flags, eni_size_weights, estimated_loop_iterations_int(), loop::num, optimize_loop_for_size_p(), tree_num_loop_insns(), and tree_unswitch_single_loop().

static struct loop * tree_unswitch_loop ( struct loop loop,
basic_block  unswitch_on,
tree  cond 

Loop unswitching. Copyright (C) 2004-2013 Free Software Foundation, Inc.

This file is part of GCC.

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You should have received a copy of the GNU General Public License along with GCC; see the file COPYING3. If not see http://www.gnu.org/licenses/.

   This file implements the loop unswitching, i.e. transformation of loops like

   while (A)
       if (inv)


       if (!inv)

   where inv is the loop invariant, into

   if (inv)
       while (A)
       while (A)

   Inv is considered invariant iff the values it compares are both invariant;
   tree-ssa-loop-im.c ensures that all the suitable conditions are in this
   Unswitch a LOOP w.r. to given basic block UNSWITCH_ON.  We only support
   unswitching of innermost loops.  COND is the condition determining which
   loop is entered -- the new loop is entered if COND is true.  Returns NULL
   if impossible, new loop otherwise.  
     Some sanity checking.  
static bool tree_unswitch_single_loop ( struct loop ,

Referenced by tree_ssa_unswitch_loops().

static bool tree_unswitch_single_loop ( )
   Unswitch single LOOP.  NUM is number of unswitchings done; we do not allow
   it to grow too much, it is too easy to create example on that the code would
   grow exponentially.  
         Find a bb to unswitch on.  
             Remove false path.  
             Remove true path.  
         Do not unswitch too much.  
         In nested tree_unswitch_single_loop first optimize all conditions
         using entry checks, then discover still reachable blocks in the
         loop and find the condition only among those still reachable bbs.  
         When called recursively, first do a quick discovery
         of reachable bbs after the above changes and only
         consider conditions in still reachable bbs.  
         Start with marking header.  
         Iterate: find everything reachable from what we've already seen
         within the same innermost loop.  Don't look through false edges
         if condition is always true or true edges if condition is
         always false.  
         Find a bb to unswitch on.  
     Unswitch the loop on this condition.  
     Update the SSA form after unswitching.  
     Invoke itself on modified loops.  

References changed, dump_file, dump_flags, free(), gimple_cond_set_condition_from_tree(), integer_nonzerop(), integer_zerop(), last_stmt(), loop::num_nodes, simplify_using_entry_checks(), tree_may_unswitch_on(), and update_stmt().