missing file in gcc-4.3.1

[collinr@ensisun.imag.fr]

Good morning,
I am working on gcc, and I am looking for information about "liveness  
analysis". The manual gccint.pdf says on page 101 :

"Life analysis
This pass computes which pseudo-registers are live at each point in  
the program, and makes the first instruction that uses a value point  
at the instruction that computed the value. It then deletes  
computations whose results are never used, and combines memory  
references with add or subtract instructions to make autoincrement or  
autodecrement addressing. The pass is located in ?flow.c?."

However, I found flow.c in gcc-3.3, but not in gcc-4.3.1
Could you explain me that?

Regards,
Rémi Collin