• Heinz Saathoff (65/65) Dec 11 2006 Hello Walter,

Heinz Saathoff <newshsaat arcor.de> writes:

Hello Walter,


I compiled this code 

--------- code ---------
#include <dos.h>
#include <string>
#include <vector>

struct SInOut {
   std::string   in_name;
   std::string   out_name;
};

std::vector<SInOut>  io_names;

void AddExpandedWild(const char *arg)
{
   SInOut names;
   for(FIND *f = findfirst(arg, 0); f!=0; f=findnext()) {
      names.in_name = f->name;
      io_names.push_back(names);
   }//for
}//AddExpandedWild
------ end code --------

with this complier switches
 dmc -IE:\dm\stlport\stlport -Ae -o+all -c example.cpp
and disassembled the resulting OBJ-file. In the disassembled code I 
found many unnecessary instructions and wondered why they are included.
Part of the diessassembled code shown here:

             [snip]
L8E:		mov	dword ptr -4[EBP],0FFFFFFFFh     <---- ???
		mov	dword ptr -4[EBP],3              <---- ???
		mov	dword ptr -4[EBP],4              <---- ???
		mov	dword ptr -4[EBP],3              <---- ???
		mov	dword ptr -4[EBP],5              <---- ???
		mov	dword ptr -4[EBP],3              <---- ???
		mov	dword ptr -4[EBP],6              
		mov	EAX,-018h[EBP]
		lea	ECX,-018h[EBP]
		sub	EAX,-020h[EBP]
		push	EAX
		push	dword ptr -020h[EBP]
		call	near ptr void syscall 
std::D::d::allocator<>::deallocate(char *,unsigned )const 
		mov	dword ptr -4[EBP],3            <---- ???
		mov	dword ptr -4[EBP],7            <---- ???
		mov	dword ptr -4[EBP],3            <---- ???
		mov	dword ptr -4[EBP],0FFFFFFFFh   <---- ???
		mov	dword ptr -4[EBP],8            <---- ???
		mov	dword ptr -4[EBP],0FFFFFFFFh   <---- ???
		mov	dword ptr -4[EBP],9
		mov	EBX,-024h[EBP]
		lea	ECX,-024h[EBP]
		sub	EBX,-02Ch[EBP]
		push	EBX
		push	dword ptr -02Ch[EBP]
		call	near ptr void syscall 
std::D::d::allocator<>::deallocate(char *,unsigned )const 
		mov	dword ptr -4[EBP],0FFFFFFFFh   <---- ???
		mov	dword ptr -4[EBP],0Ah          <---- ???
		mov	dword ptr -4[EBP],0FFFFFFFFh
		mov	EAX,-0Ch[EBP]
		mov	FS:__except_list,EAX
	       [snip]

I assume that this moves have something to do with exception handling. 
But I would also assume that the optimizer should be able to remove the 
unnecessary moves.  
BTW, Compiler version from SCPPN.EXE is 8.48.10n


- Heinz