Question about RTL code hoisting

[Jie Zhang <jie at codesourcery dot com>]

I just found that the current RTL code hoisting cannot optimize

REG = ...
if (cond)
  {
    r0 = REG;
    ....
  }
else
  {
    r0 = REG;
    ...
  }

to


REG = ...
r0 = REG;
if (cond)
  {
    ....
  }
else
  {
    ...
  }

where REG is a pseudo register and r0 is a physical register. I have 
looked at the code of RTL hoisting pass. But I cannot find a simple way 
to extend it to deal with this case. And the hoisting pass is only 
enabled when -Os. So I'm going to implement another hoisting pass to do 
this optimization. Is it a good idea? Does anyone know if there is an 
existing pass which should have handled or be able to be easily adapted 
to handle this case? Thanks!


--
Jie Zhang
CodeSourcery
(650) 331-3385 x735