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{
Common subexpression elimination on base blocks
Copyright (c) 2005 by 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 optcse;
{$i fpcdefs.inc}
interface
procedure docse(rootnode : tnode);
implementation
procedure docse(rootnode : tnode);
begin
{ create a linear list of nodes }
{ create hash values }
{ sort by hash values, taking care of nf_csebarrier and keeping the
original order of the nodes }
{ compare nodes with equal hash values }
{ search barrier }
for i:=0 to nodelist.length-1 do
begin
{ and then search backward so we get always the largest equal trees }
j:=i+1;
{ collect equal nodes }
while (j<=nodelist.length-1) and
nodelist[i].docompare(nodelist[j]) do
inc(j);
dec(j);
if j>i then
begin
{ cse found }
{ create temp. location }
{ replace first node by
- temp. creation
- expression calculation
- assignment of expression to temp. }
tempnode:=ctempcreatenode.create(nodelist[i].resulttype,nodelist[i].resulttype.def.size,tt_persistent,
nodelist[i].resulttype.def.is_intregable or nodelist[i].resulttype.def.is_fpuregable);
addstatement(createstatement,tempnode);
addstatement(createstatement,cassignmentnode.create(ctemprefnode.create(tempnode),
caddrnode.create_internal(para.left)));
para.left := ctypeconvnode.create_internal(cderefnode.create(ctemprefnode.create(tempnode)),para.left.resulttype);
addstatement(deletestatement,ctempdeletenode.create(tempnode));
{ replace next nodes by loading the temp. reference }
{ replace last node by loading the temp. reference and
delete the temp. }
end;
end;
end;
end.
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