Re: optimization/6880: Inlining inefficiencies

[Dan Nicolaescu <dann@ics.uci.edu>]

The following reply was made to PR optimization/6880; it has been noted by GNATS.

From: Dan Nicolaescu <dann@ics.uci.edu>
To: Dara Hazeghi <dhazeghi@yahoo.com>
Cc: gcc-gnats@gcc.gnu.org
Subject: Re: optimization/6880: Inlining inefficiencies
Date: Sun, 11 May 2003 02:04:06 -0700

 The problem still occurs in mainline CVS. 
 
 But it is not caused by inlining. The problem is the compiler
 generated copy constructor. 
 
 Given the following code:
 
 class Complex {
 public:
     int re, im;
     Complex( int r, int i ) : re(r), im(i) {}
 #ifdef MYCONSTRUCTOR
     Complex( const Complex & F ) : re(F.re), im(F.im) {}
 #endif
     Complex() {}
 };
 
 Complex Yy;
 
 void oop_style()
 {
   Complex factor (53, 37);
   Yy = factor;
 }
 
 The oop_style function is compiled to (on x86):
    
 _Z9oop_stylev:
 .LFB11:
         subl    $12, %esp       #,
 .LCFI0:
         movl    $53, (%esp)     #,                                 
         movl    (%esp), %edx    #, tmp64
         movl    $37, 4(%esp)    #, <variable>.im  
         movl    4(%esp), %ecx   #,                
         movl    %edx, Yy        # tmp64, 
         movl    %ecx, Yy+4      #,
         addl    $12, %esp       #,
         ret
      
 when using g++ -O3   -fverbose-asm -fomit-frame-pointer
        
 and to:
      
 _Z9oop_stylev:
 .LFB14:
         subl    $28, %esp       #,
 .LCFI0:
         movl    $53, %eax       #,
         movl    $37, %edx       #,
         movl    %eax, Yy        #,
         movl    %edx, Yy+4      #,
         addl    $28, %esp       #,
         ret
   
   
 when using g++ -O3 -DMYCONSTRUCTOR  -fverbose-asm -fomit-frame-pointer
   
 Note the extra move to the stack when using the compiler generated
 constructor.
 
 Can the name of the bug be changed to "Inefficient compiler generated
 copy constructor" and be moved to the C++ category? Or should I file
 a new bug report?