GCC 4.9 generates bigger code for x86

[David Guillen Fandos]

Hi all,

I just noticed that 4.9 generates some code overhead for 386 machines 
respect to 4.8.
In my test case I used 4.8.1 and 4.9.1 and realized that when compiling 
with "-Os -fno-exceptions -fno-align-functions -fomit-frame-pointer" 
certain things change:

On 4.9 the backend adds some "nop" after ret or jmp.
It also stops using "leave" instruction, which is really convenient to 
save some instructions.

It think it is not using leave because of register allocation. In 4.8 a 
function starts like this:

     390:    55                       push   %ebp
     391:    89 e5                    mov    %esp,%ebp
     393:    53                       push   %ebx

Whereas in 4.9 it starts:

     386:    53                       push   %ebx
     387:    89 cb                    mov    %ecx,%ebx
     389:    83 ec 28                 sub    $0x28,%esp

So the first function actually saves some space.

Any ideas, thoughts, comments?

Thanks a lot,
David G.F.