* Before r35961 (back in 2017) some simple assignment optimizations, such as "x:=x+y" to "inc(x,y)", were performed when -O2 in tassignmentnode.simplify. In r35961 these optimizations were moved to a separate pass which is enabled only when -O3 by cs_opt_use_load_modify_store. This separate pass can benefit from other optimization. But worse code is generated with -O2 since then.

This commit restores applying of simple assignment optimizations when -O2.

compiler/nld.pas

@@ -197,7 +197,8 @@ implementation
       cpuinfo,
       htypechk,pass_1,procinfo,paramgr,
       nbas,ncon,nflw,ninl,ncnv,nmem,ncal,nutils,
-      cgbase
+      cgbase,
+      optloadmodifystore
       ;
 
 
@@ -625,6 +626,13 @@ implementation
            is_constrealnode(right) and
            not equal_defs(right.resultdef,left.resultdef) then
           inserttypeconv(right,left.resultdef);
+{$if (cs_opt_use_load_modify_store in supported_optimizerswitches)}
+        { Perform simple optimizations when -O2 and the dedicated
+          cs_opt_use_load_modify_store optimization pass is not enabled. }
+        if (cs_opt_level2 in current_settings.optimizerswitches) and
+           not (cs_opt_use_load_modify_store in current_settings.optimizerswitches) then
+          result:=try_opt_assignmentnode(self);
+{$endif}
       end;
 
 

compiler/optloadmodifystore.pas

@@ -38,16 +38,17 @@ unit optloadmodifystore;
   interface
 
     uses
-      node;
+      node,nld;
 
     procedure do_optloadmodifystore(var rootnode : tnode);
+    function try_opt_assignmentnode(assignmentnode : tassignmentnode): tnode;
 
   implementation
 
     uses
-      globtype,verbose,nutils,compinnr,
+      globtype,globals,verbose,nutils,compinnr,
       defutil,defcmp,htypechk,pass_1,constexp,
-      nadd,ncal,ncon,ncnv,ninl,nld,nmat,
+      nadd,ncal,ncon,ncnv,ninl,nmat,
       symdef;
 
     function try_opt_assignmentnode(assignmentnode: tassignmentnode): tnode;
@@ -57,6 +58,10 @@ unit optloadmodifystore;
         result:=nil;
         with assignmentnode do
           begin
+            { *** Here are simple optimizations which are performed
+              when -O2 (via a call from tassignmentnode.simplify) or
+              when cs_opt_use_load_modify_store is enabled (in a separate pass).
+            }
             { replace i:=succ/pred(i) by inc/dec(i)? }
             if (right.nodetype=inlinen) and
               ((tinlinenode(right).inlinenumber=in_succ_x) or (tinlinenode(right).inlinenumber=in_pred_x)) and
@@ -273,6 +278,71 @@ unit optloadmodifystore;
                 taddnode(ttypeconvnode(right).left).left:=nil;