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+{
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+ Dead store elimination
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+
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+ Copyright (c) 2005-2012 by Jeppe Johansen and Florian Klaempfl
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+
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+ This program is free software; you can redistribute it and/or modify
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+ it under the terms of the GNU General Public License as published by
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+ the Free Software Foundation; either version 2 of the License, or
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+ (at your option) any later version.
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+
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+ This program is distributed in the hope that it will be useful,
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+ but WITHOUT ANY WARRANTY; without even the implied warranty of
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+ MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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+ GNU General Public License for more details.
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+
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+ You should have received a copy of the GNU General Public License
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+ along with this program; if not, write to the Free Software
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+ Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
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+
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+ ****************************************************************************
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+}
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+unit optdeadstore;
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+
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+{$i fpcdefs.inc}
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+
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+{ $define DEBUG_DEADSTORE}
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+
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+ interface
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+
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+ uses
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+ node;
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+
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+ function do_optdeadstoreelim(var rootnode : tnode) : tnode;
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+
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+ implementation
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+
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+ uses
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+ verbose,globtype,
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+ fmodule,
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+ procinfo,pass_1,
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+ nutils,
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+ nbas,nld,nmem,nflw,nset,
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+ optbase,
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+ symsym,symconst;
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+
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+
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+ function deadstoreelim(var n: tnode; arg: pointer): foreachnoderesult;
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+ var
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+ a: tassignmentnode;
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+ redundant: boolean;
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+ begin
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+ result:=fen_true;
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+ if (n.nodetype=statementn) and
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+ assigned(tstatementnode(n).statement) then
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+ begin
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+ if tstatementnode(n).statement.nodetype=assignn then
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+ begin
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+ a:=tassignmentnode(tstatementnode(n).statement);
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+
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+ { we need to have dfa for the node }
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+ if assigned(a.left.optinfo) and
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+ (a.left.optinfo^.index<>aword(-1)) and
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+ { node must be either a local or parameter load node }
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+ (((a.left.nodetype=loadn) and
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+ (tloadnode(a.left).symtableentry.typ=localvarsym) and
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+ (tloadnode(a.left).symtable=current_procinfo.procdef.localst)) or
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+ ((a.left.nodetype=loadn) and
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+ (tloadnode(a.left).symtableentry.typ=paravarsym) and
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+ (tloadnode(a.left).symtable=current_procinfo.procdef.parast) and
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+ (tparavarsym(tloadnode(a.left).symtableentry).varspez in [vs_const,vs_value]))
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+ ) and
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+ not(might_have_sideeffects(a.right)) then
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+ begin
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+ redundant:=not(assigned(a.successor)) or not(DFASetIn(a.successor.optinfo^.life,a.left.optinfo^.index));
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+
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+ if redundant then
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+ begin
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+{$ifdef DEBUG_DEADSTORE}
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+ writeln('************************** Redundant write *********************************');
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+ printnode(a);
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+ writeln('****************************************************************************');
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+{$endif DEBUG_DEADSTORE}
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+ pboolean(arg)^:=true;
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+
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+ tstatementnode(n).statement.free;
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+
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+ tstatementnode(n).statement:=cnothingnode.create;
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+ Exclude(tstatementnode(n).flags, nf_pass1_done);
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+ do_firstpass(n);
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+ end
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+ end;
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+ end;
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+ end;
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+ end;
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+
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+
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+ function do_optdeadstoreelim(var rootnode: tnode): tnode;
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+ var
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+ changed: boolean;
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+ begin
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+ if not(pi_dfaavailable in current_procinfo.flags) then
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+ internalerror(2013110201);
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+ if not current_procinfo.has_nestedprocs then
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+ begin
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+ changed:=false;
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+ foreachnodestatic(pm_postprocess, rootnode, @deadstoreelim, @changed);
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+ end;
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+ result:=rootnode;
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+ end;
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+
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+end.
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+
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florian