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{
Dead store elimination
Copyright (c) 2005-2012 by Jeppe Johansen and Florian Klaempfl
This program 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 2 of the License, or
(at your option) any later version.
This program 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 this program; if not, write to the Free Software
Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
****************************************************************************
}
unit optdeadstore;
{$i fpcdefs.inc}
{ $define DEBUG_DEADSTORE}
{ $define EXTDEBUG_DEADSTORE}
interface
uses
node;
function do_optdeadstoreelim(var rootnode : tnode) : tnode;
implementation
uses
verbose,globtype,globals,
procinfo,pass_1,
nutils,
nbas,nld,
optbase,
symsym,symconst;
function deadstoreelim(var n: tnode; arg: pointer): foreachnoderesult;
var
a: tassignmentnode;
redundant: boolean;
begin
result:=fen_true;
if (n.nodetype=statementn) and
assigned(tstatementnode(n).statement) then
begin
if tstatementnode(n).statement.nodetype=assignn then
begin
a:=tassignmentnode(tstatementnode(n).statement);
{ we need to have dfa for the node }
if assigned(a.left.optinfo) and
(a.left.optinfo^.index<>aword(-1)) and
{ node must be either a local or parameter load node }
(a.left.nodetype=loadn) and
{ its address cannot have escaped the current routine }
not(tabstractvarsym(tloadnode(a.left).symtableentry).addr_taken) and
((
(tloadnode(a.left).symtableentry.typ=localvarsym) and
(tloadnode(a.left).symtable=current_procinfo.procdef.localst)) or
((tloadnode(a.left).symtableentry.typ=paravarsym) and
(tloadnode(a.left).symtable=current_procinfo.procdef.parast) and
(tparavarsym(tloadnode(a.left).symtableentry).varspez in [vs_const,vs_value])) or
((tloadnode(a.left).symtableentry.typ=staticvarsym) and
(tloadnode(a.left).symtable.symtabletype=staticsymtable) and
(current_procinfo.procdef.proctypeoption<>potype_unitinit) and
not(vsa_different_scope in tstaticvarsym(tloadnode(a.left).symtableentry).varsymaccess)
)
) and
((a.right.nodetype in [niln,stringconstn,pointerconstn,setconstn,guidconstn]) or
((a.right.nodetype=ordconstn) and not(cs_check_range in current_settings.localswitches)) or
((a.right.nodetype=realconstn) and not(cs_ieee_errors in current_settings.localswitches)) or
((cs_opt_dead_values in current_settings.optimizerswitches) and not(might_have_sideeffects(a.right)))
) then
begin
redundant:=not(assigned(a.successor)) or not(DFASetIn(a.successor.optinfo^.life,a.left.optinfo^.index));
if redundant then
begin
{$ifdef DEBUG_DEADSTORE}
writeln('************************** Redundant write *********************************');
printnode(a);
writeln('****************************************************************************');
{$endif DEBUG_DEADSTORE}
pboolean(arg)^:=true;
tstatementnode(n).statement.free;
tstatementnode(n).statement:=cnothingnode.create;
{ do not run firstpass on n here, as it will remove the statement node
and this will make foreachnodestatic process the wrong nodes as the current statement
node will disappear }
end
end;
end;
end;
end;
function do_optdeadstoreelim(var rootnode: tnode): tnode;
var
changed: boolean;
begin
{$ifdef EXTDEBUG_DEADSTORE}
writeln('******************* Tree before deadstore elimination **********************');
printnode(rootnode);
writeln('****************************************************************************');
{$endif EXTDEBUG_DEADSTORE}
if not(pi_dfaavailable in current_procinfo.flags) then
internalerror(2013110201);
changed:=false;
if not current_procinfo.has_nestedprocs then
foreachnodestatic(pm_postprocess, rootnode, @deadstoreelim, @changed);
{$ifdef DEBUG_DEADSTORE}
if changed then
begin
writeln('******************** Tree after deadstore elimination **********************');
printnode(rootnode);
writeln('****************************************************************************');
end;
{$endif DEBUG_DEADSTORE}
result:=rootnode;
end;
end.
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