1 files changed, 79 insertions, 0 deletions
diff --git a/compiler/optcse.pas b/compiler/optcse.pas
new file mode 100644
index 0000000000..9eaecd8290
--- /dev/null
+++ b/compiler/optcse.pas
@@ -0,0 +1,79 @@
+{
+    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.