Thumb optimization question

[Ivan Petrov]

I have one question. So... have small sample programm.

[code]
int bar( int );

int foo( int a, int b )
{
   return bar( a + b );
}
[/code]
 
If I compille it with out -thumb parameter, i have very clean code.
 
 add r0, r1, r0
bx lr
 
But with -thumb parameter have unopimized code.

add r1, r1, r0
mov r0, r1
bx lr
 
All diff of it outrage on '*.27.combine' (key -da) optimization step. But I long time can't understad how it work.
Can anybody help me with it?

--
Regards, Ivan