/usr/share/fpcsrc/2.6.2/compiler/optcse.pas is in fpc-source-2.6.2 2.6.2-8.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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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}
{ $define csedebug}
{ $define csestats}
interface
uses
node;
{
the function creates non optimal code so far:
- call para nodes are cse barriers because they can be reordered and thus the
temp. creation can be done too late
- cse's in chained expressions are not recognized: the common subexpression
in (a1 and b and c) vs. (a2 and b and c) is not recognized because there is no common
subtree b and c
- the cse knows nothing about register pressure. In case of high register pressure, cse might
have a negative impact
- assignment nodes are currently cse borders: things like a[i,j]:=a[i,j]+1; are not improved
- the list of cseinvariant node types and inline numbers is not complete yet
Further, it could be done probably in a faster way though the complexity can't probably not reduced
}
function do_optcse(var rootnode : tnode) : tnode;
implementation
uses
globtype,
cclasses,
verbose,
nutils,
procinfo,
nbas,nld,ninl,ncal,ncnv,nadd,
pass_1,
symconst,symtype,symdef,symsym,
defutil,
optbase;
const
cseinvariant : set of tnodetype = [addn,muln,subn,divn,slashn,modn,andn,orn,xorn,notn,vecn,
derefn,equaln,unequaln,ltn,gtn,lten,gten,typeconvn,subscriptn,
inn,symdifn,shrn,shln,ordconstn,realconstn,unaryminusn,pointerconstn,stringconstn,setconstn,
isn,asn,starstarn,nothingn,temprefn,loadparentfpn {,callparan}];
function searchsubdomain(var n:tnode; arg: pointer) : foreachnoderesult;
begin
if (n.nodetype in cseinvariant) or
((n.nodetype=inlinen) and
(tinlinenode(n).inlinenumber in [in_assigned_x])
) or
((n.nodetype=loadn) and
not((tloadnode(n).symtableentry.typ in [staticvarsym,localvarsym,paravarsym]) and
(vo_volatile in tabstractvarsym(tloadnode(n).symtableentry).varoptions))
) then
result:=fen_true
else
begin
pboolean(arg)^:=false;
result:=fen_norecurse_true;
end;
end;
type
tlists = record
nodelist : tfplist;
locationlist : tfplist;
equalto : tfplist;
refs : tfplist;
avail : TDFASet;
end;
plists = ^tlists;
{ collectnodes needs the address of itself to call foreachnodestatic,
so we need a wrapper because @<func> inside <func doesn't work }
function collectnodes(var n:tnode; arg: pointer) : foreachnoderesult;forward;
function collectnodes2(var n:tnode; arg: pointer) : foreachnoderesult;
begin
result:=collectnodes(n,arg);
end;
function collectnodes(var n:tnode; arg: pointer) : foreachnoderesult;
var
i,j : longint;
begin
result:=fen_false;
{ don't add the tree below an untyped const parameter: there is
no information available that this kind of tree actually needs
to be addresable, this could be improved }
if ((n.nodetype=callparan) and
(tcallparanode(n).left.resultdef.typ=formaldef) and
(tcallparanode(n).parasym.varspez=vs_const)) then
begin
result:=fen_norecurse_false;
exit;
end;
{ so far, we can handle only nodes being read }
if (n.flags*[nf_write,nf_modify]=[]) and
{ node possible to add? }
assigned(n.resultdef) and
(tstoreddef(n.resultdef).is_intregable or tstoreddef(n.resultdef).is_fpuregable) and
{ is_int/fpuregable allows arrays and records to be in registers, cse cannot handle this }
not(n.resultdef.typ in [arraydef,recorddef]) and
{ same for voiddef }
not(is_void(n.resultdef)) and
{ adding tempref nodes is worthless but their complexity is probably <= 1 anyways }
not(n.nodetype in [temprefn]) and
{ node worth to add?
We consider almost every node because even loading a variables from
a register instead of memory is more beneficial. This behaviour should
not increase register pressure because if a variable is already
in a register, the reg. allocator can merge the nodes. If a variable
is loaded from memory, loading this variable and spilling another register
should not add a speed penalty.
}
{
load nodes are not considered if they load para or local symbols from the
current stack frame, those are in registers anyways if possible
}
(not(n.nodetype=loadn) or
not(tloadnode(n).symtableentry.typ in [paravarsym,localvarsym]) or
(tloadnode(n).symtable.symtablelevel<>current_procinfo.procdef.parast.symtablelevel)
) and
{
Const nodes however are only considered if their complexity is >1
This might be the case for the risc architectures if they need
more than one instruction to load this particular value
}
(not(is_constnode(n)) or (node_complexity(n)>1)) then
begin
plists(arg)^.nodelist.Add(n);
plists(arg)^.locationlist.Add(@n);
plists(arg)^.refs.Add(nil);
plists(arg)^.equalto.Add(pointer(-1));
DFASetInclude(plists(arg)^.avail,plists(arg)^.nodelist.count-1);
for i:=0 to plists(arg)^.nodelist.count-2 do
begin
if tnode(plists(arg)^.nodelist[i]).isequal(n) and DFASetIn(plists(arg)^.avail,i) then
begin
{ use always the first occurence }
if plists(arg)^.equalto[i]<>pointer(-1) then
plists(arg)^.equalto[plists(arg)^.nodelist.count-1]:=plists(arg)^.equalto[i]
else
plists(arg)^.equalto[plists(arg)^.nodelist.count-1]:=pointer(ptrint(i));
plists(arg)^.refs[i]:=pointer(plists(arg)^.refs[i])+1;
break;
end;
end;
{ boolean and/or require a special handling: after evaluating the and/or node,
the expressions of the right side might not be available due to short boolean
evaluation, so after handling the right side, mark those expressions
as unavailable }
if (n.nodetype in [orn,andn]) and is_boolean(taddnode(n).left.resultdef) then
begin
foreachnodestatic(pm_postprocess,taddnode(n).left,@collectnodes2,arg);
j:=plists(arg)^.nodelist.count;
foreachnodestatic(pm_postprocess,taddnode(n).right,@collectnodes2,arg);
for i:=j to plists(arg)^.nodelist.count-1 do
DFASetExclude(plists(arg)^.avail,i);
result:=fen_norecurse_false;
end;
end;
end;
function searchcsedomain(var n: tnode; arg: pointer) : foreachnoderesult;
var
csedomain : boolean;
lists : tlists;
templist : tfplist;
i : longint;
def : tstoreddef;
nodes : tblocknode;
creates,
statements : tstatementnode;
hp : ttempcreatenode;
begin
result:=fen_false;
if n.nodetype in cseinvariant then
begin
csedomain:=true;
foreachnodestatic(pm_postprocess,n,@searchsubdomain,@csedomain);
{ found a cse domain }
if csedomain then
begin
statements:=nil;
result:=fen_norecurse_true;
{$ifdef csedebug}
writeln('============ cse domain ==================');
printnode(output,n);
writeln('Complexity: ',node_complexity(n));
{$endif csedebug}
lists.nodelist:=tfplist.create;
lists.locationlist:=tfplist.create;
lists.equalto:=tfplist.create;
lists.refs:=tfplist.create;
foreachnodestatic(pm_postprocess,n,@collectnodes,@lists);
templist:=tfplist.create;
templist.count:=lists.nodelist.count;
{ check all nodes if one is used more than once }
for i:=0 to lists.nodelist.count-1 do
begin
{ current node used more than once? }
if assigned(lists.refs[i]) then
begin
if not(assigned(statements)) then
begin
nodes:=internalstatements(statements);
addstatement(statements,internalstatements(creates));
end;
def:=tstoreddef(tnode(lists.nodelist[i]).resultdef);
templist[i]:=ctempcreatenode.create_value(def,def.size,tt_persistent,
def.is_intregable or def.is_fpuregable,tnode(lists.nodelist[i]));
{ make debugging easier and set temp. location to the original location }
tnode(templist[i]).fileinfo:=tnode(lists.nodelist[i]).fileinfo;
addstatement(creates,tnode(templist[i]));
{ make debugging easier and set temp. location to the original location }
creates.fileinfo:=tnode(lists.nodelist[i]).fileinfo;
hp:=ttempcreatenode(templist[i]);
do_firstpass(tnode(hp));
templist[i]:=hp;
pnode(lists.locationlist[i])^:=ctemprefnode.create(ttempcreatenode(templist[i]));
{ make debugging easier and set temp. location to the original location }
pnode(lists.locationlist[i])^.fileinfo:=tnode(lists.nodelist[i]).fileinfo;
do_firstpass(pnode(lists.locationlist[i])^);
{$ifdef csedebug}
printnode(output,statements);
{$endif csedebug}
end
{ current node reference to another node? }
else if lists.equalto[i]<>pointer(-1) then
begin
{$if defined(csedebug) or defined(csestats)}
printnode(output,tnode(lists.nodelist[i]));
writeln(i,' equals ',ptrint(lists.equalto[i]));
printnode(output,tnode(lists.nodelist[ptrint(lists.equalto[i])]));
{$endif defined(csedebug) or defined(csestats)}
templist[i]:=templist[ptrint(lists.equalto[i])];
pnode(lists.locationlist[i])^:=ctemprefnode.create(ttempcreatenode(templist[ptrint(lists.equalto[i])]));
{ make debugging easier and set temp. location to the original location }
pnode(lists.locationlist[i])^.fileinfo:=tnode(lists.nodelist[i]).fileinfo;
do_firstpass(pnode(lists.locationlist[i])^);
end;
end;
{ clean up unused trees }
for i:=0 to lists.nodelist.count-1 do
if lists.equalto[i]<>pointer(-1) then
tnode(lists.nodelist[i]).free;
{$ifdef csedebug}
writeln('nodes: ',lists.nodelist.count);
writeln('==========================================');
{$endif csedebug}
lists.nodelist.free;
lists.locationlist.free;
lists.equalto.free;
lists.refs.free;
templist.free;
if assigned(statements) then
begin
{ call para nodes need a special handling because
they can be only children nodes of call nodes
so the initialization code is inserted below the
call para node
}
if n.nodetype=callparan then
begin
addstatement(statements,tcallparanode(n).left);
tcallparanode(n).left:=nodes;
do_firstpass(tcallparanode(n).left);
end
else
begin
addstatement(statements,n);
n:=nodes;
do_firstpass(n);
end;
{$ifdef csedebug}
printnode(output,nodes);
{$endif csedebug}
end;
end
end;
end;
function do_optcse(var rootnode : tnode) : tnode;
begin
foreachnodestatic(pm_postprocess,rootnode,@searchcsedomain,nil);
result:=nil;
end;
end.
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