Functions
static void	copy_rename_partition_coalesce ()
static unsigned int	rename_ssa_copies ()
static bool	gate_copyrename ()
gimple_opt_pass *	make_pass_rename_ssa_copies ()

Variables
struct {
int coalesced
}	stats

Function Documentation

static void copy_rename_partition_coalesce ( )

static

The following routines implement the SSA copy renaming phase.

   This optimization looks for copies between 2 SSA_NAMES, either through a
   direct copy, or an implicit one via a PHI node result and its arguments.

   Each copy is examined to determine if it is possible to rename the base
   variable of one of the operands to the same variable as the other operand.
   i.e.
   T.3_5 = <blah>
   a_1 = T.3_5

   If this copy couldn't be copy propagated, it could possibly remain in the
   program throughout the optimization phases.   After SSA->normal, it would
   become:

   T.3 = <blah>
   a = T.3

   Since T.3_5 is distinct from all other SSA versions of T.3, there is no
   fundamental reason why the base variable needs to be T.3, subject to
   certain restrictions.  This optimization attempts to determine if we can
   change the base variable on copies like this, and result in code such as:

   a_5 = <blah>
   a_1 = a_5

   This gives the SSA->normal pass a shot at coalescing a_1 and a_5. If it is
   possible, the copy goes away completely. If it isn't possible, a new temp
   will be created for a_5, and you will end up with the exact same code:

   a.8 = <blah>
   a = a.8

   The other benefit of performing this optimization relates to what variables
   are chosen in copies.  Gimplification of the program uses temporaries for
   a lot of things. expressions like

   a_1 = <blah>
   <blah2> = a_1

   get turned into

   T.3_5 = <blah>
   a_1 = T.3_5
   <blah2> = a_1

   Copy propagation is done in a forward direction, and if we can propagate
   through the copy, we end up with:

   T.3_5 = <blah>
   <blah2> = T.3_5

   The copy is gone, but so is all reference to the user variable 'a'. By
   performing this optimization, we would see the sequence:

   a_5 = <blah>
   a_1 = a_5
   <blah2> = a_1

   which copy propagation would then turn into:

   a_5 = <blah>
   <blah2> = a_5

   and so we still retain the user variable whenever possible.

Coalesce the partitions in MAP representing VAR1 and VAR2 if it is valid.
   Choose a representative for the partition, and send debug info to DEBUG.

References cfun, partition_to_var(), print_generic_expr(), register_ssa_partition(), replace_ssa_name_symbol(), ssa_default_def(), types_compatible_p(), and _var_map::var_partition.

Referenced by rename_ssa_copies().

static bool gate_copyrename ( )

static

Return true if copy rename is to be performed.

gimple_opt_pass* make_pass_rename_ssa_copies ( )

static unsigned int rename_ssa_copies ( )

static

This function will make a pass through the IL, and attempt to coalesce any
   SSA versions which occur in PHI's or copies.  Coalescing is accomplished by
   changing the underlying root variable of all coalesced version.  This will
   then cause the SSA->normal pass to attempt to coalesce them all to the same
   variable.

References cfun, copy_rename_partition_coalesce(), debug, delete_var_map(), dump_file, dump_flags, dump_var_map(), gimple_assign_lhs(), gimple_assign_rhs1(), gimple_assign_ssa_name_copy_p(), gimple_phi_num_args(), gimple_phi_result(), gsi_end_p(), gsi_next(), gsi_start_bb(), gsi_start_phis(), gsi_stmt(), init_var_map(), map, memset(), partition_to_var(), print_generic_expr(), replace_ssa_name_symbol(), statistics_counter_event(), stats, _var_map::var_partition, and virtual_operand_p().

Variable Documentation

int coalesced

struct { ... } stats

@verbatim Rename SSA copies.

This file is part of GCC.

GCC is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 3, or (at your option) any later version.

GCC is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

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/.

Referenced by rename_ssa_copies().

Functions

Variables

Function Documentation

Variable Documentation