Infinite loop in init_alias_analysis

[Christian Iseli]

Hi there,

I got an infinite loop while compiling sone test code here.  I think I have 
tracked down the
problem to the new (as of snapshot 971031) code in alias.c, in the 
init_alias_analysis routine,
in the while (changed) loop.

Things happen in the following way:
- During the first iteration of the loop, new_reg_base_value[24] is set to 
(address (reg:HI 1 %r3)),
  (reg 1 is a FUNCTION_ARG_REGNO_P) while copying_arguments is true.
- Later in the function, new_reg_base_value[1] is set to (reg/v:HI 24)

- Now the first iteration terminates and the values from new_reg_base_value 
are copied into
  reg_base_value.
- In the next loop iteration, find_base_value is called and promptly returns 
the values it finds
  in reg_base_value, which yields to new_reg_base_value[24] => (reg/v:HI 24) 
and
  new_reg_base_value[1] => (address (reg:HI 1 %r3))
- And so on...

I'm not sure what's the best fix...
  - set reg_seen of the argument register when it is copied to the pseudo ?
  - avoid the part before NOTE_INSN_FUNCTION_BEG in subsequent loop iterations 
?
  - do some clever testing of new_reg_base_value and reg_base_value ?
  - reverse the if statements in the REG case in find_base_value ?

What do you think?

					Christian