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tree-outof-ssa.c (insert_backedge_copies): New function. 

* tree-outof-ssa.c (insert_backedge_copies): New function.
        (rewrite_out_of_ssa): Use it.

From-SVN: r92711
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Jeff Law 2004-12-29 12:21:07 -07:00 committed by Jeff Law
parent 263db5562a
commit 06170e1d31
2 changed files with 102 additions and 0 deletions
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gcc/ChangeLog
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@ -1,3 +1,8 @@
2004-12-29 Jeff Law <law@redhat.com>
* tree-outof-ssa.c (insert_backedge_copies): New function.
(rewrite_out_of_ssa): Use it.
2004-12-29 Ira Rosen <irar@il.ibm.com>
PR tree-optimization/18179

97
gcc/tree-outof-ssa.c
View File

@ -2362,6 +2362,95 @@ remove_ssa_form (FILE *dump, var_map map, int flags)
dump_file = save;
}
/* Search every PHI node for arguments associated with backedges which
we can trivially determine will need a copy (the argument is either
not an SSA_NAME or the argument has a different underlying variable
than the PHI result).
Insert a copy from the PHI argument to a new destination at the
end of the block with the backedge to the top of the loop. Update
the PHI argument to reference this new destination. */
static void
insert_backedge_copies (void)
{
basic_block bb;
FOR_EACH_BB (bb)
{
tree phi;
for (phi = phi_nodes (bb); phi; phi = PHI_CHAIN (phi))
{
tree result = PHI_RESULT (phi);
tree result_var;
int i;
if (!is_gimple_reg (result))
continue;
result_var = SSA_NAME_VAR (result);
for (i = 0; i < PHI_NUM_ARGS (phi); i++)
{
tree arg = PHI_ARG_DEF (phi, i);
edge e = PHI_ARG_EDGE (phi, i);
/* If the argument is not an SSA_NAME, then we will
need a constant initialization. If the argument is
an SSA_NAME with a different underlying variable and
we are not combining temporaries, then we will
need a copy statement. */
if ((e->flags & EDGE_DFS_BACK)
&& (TREE_CODE (arg) != SSA_NAME
|| (!flag_tree_combine_temps
&& SSA_NAME_VAR (arg) != result_var)))
{
tree stmt, name, last = NULL;
block_stmt_iterator bsi;
bsi = bsi_last (PHI_ARG_EDGE (phi, i)->src);
if (!bsi_end_p (bsi))
last = bsi_stmt (bsi);
/* In theory the only way we ought to get back to the
start of a loop should be with a COND_EXPR or GOTO_EXPR.
However, better safe than sorry.
If the block ends with a control statment or
something that might throw, then we have to
insert this assignment before the last
statement. Else insert it after the last statement. */
if (last && stmt_ends_bb_p (last))
{
/* If the last statement in the block is the definition
site of the PHI argument, then we can't insert
anything after it. */
if (TREE_CODE (arg) == SSA_NAME
&& SSA_NAME_DEF_STMT (arg) == last)
continue;
}
/* Create a new instance of the underlying
variable of the PHI result. */
stmt = build (MODIFY_EXPR, TREE_TYPE (result_var),
NULL, PHI_ARG_DEF (phi, i));
name = make_ssa_name (result_var, stmt);
TREE_OPERAND (stmt, 0) = name;
/* Insert the new statement into the block and update
the PHI node. */
if (last && stmt_ends_bb_p (last))
bsi_insert_before (&bsi, stmt, BSI_NEW_STMT);
else
bsi_insert_after (&bsi, stmt, BSI_NEW_STMT);
modify_stmt (stmt);
SET_PHI_ARG_DEF (phi, i, name);
}
}
}
}
}
/* Take the current function out of SSA form, as described in
R. Morgan, ``Building an Optimizing Compiler'',
Butterworth-Heinemann, Boston, MA, 1998. pp 176-186. */
@ -2373,6 +2462,14 @@ rewrite_out_of_ssa (void)
int var_flags = 0;
int ssa_flags = (SSANORM_REMOVE_ALL_PHIS | SSANORM_USE_COALESCE_LIST);
/* If elimination of a PHI requires inserting a copy on a backedge,
then we will have to split the backedge which has numerous
undesirable performance effects.
A significant number of such cases can be handled here by inserting
copies into the loop itself. */
insert_backedge_copies ();
if (!flag_tree_live_range_split)
ssa_flags |= SSANORM_COALESCE_PARTITIONS;