* patch by Nico Erfurth:

Optimize ARM OP_MUL/OP_IMUL for x*ispowerof2(const+1) cases

Calculations like a*7 can be optimized to a*8-a with the usage of RSB and left
shifts which can be done in a single cycle.

git-svn-id: trunk@21351 -

compiler/arm/cgcpu.pas

@@ -766,6 +766,17 @@ unit cgcpu;
                 so.shiftimm:=l1;
                 list.concat(taicpu.op_reg_reg_reg_shifterop(A_ADD,dst,src,src,so));
               end
+            { for example : b=a*7 -> b=a*8-a with rsb instruction and shl }
+            else if (op in [OP_MUL,OP_IMUL]) and ispowerof2(a+1,l1) and not(cgsetflags or setflags) then
+              begin
+                if l1>32 then{does this ever happen?}
+                  internalerror(201205181);
+                shifterop_reset(so);
+                so.shiftmode:=SM_LSL;
+                so.shiftimm:=l1;
+                list.concat(taicpu.op_reg_reg_reg_shifterop(A_RSB,dst,src,src,so));
+              end
+
             else
               begin
                 tmpreg:=getintregister(list,size);