[tree-ssa] reaching def. question

[law@redhat.com]

In message <11A7C99E-77AD-11D8-9053-000393A91CAA@apple.com>, Devang Patel write
s:
 >
 >On Mar 16, 2004, at 4:27 PM, law@redhat.com wrote:
 >
 >> You also have to be damn careful about marking something to be 
 >> rewritten
 >> which is used in a mixed PHI node.  ie
 >>
 >> a_3 = PHI (a_2, b_1)
 >
 >This is new to me. When do I expect to see mixed PHI node? An example
 >would help me to  understand it.
It happens on a regular basis due to copy propagation.

For example if you had

  if (cond)
    a_4 = b_1;
  else
    a_2 = p + q;

  a_3 = PHI (a_2, a_4);

Copy propagation would turn the PHI into:

  a_3 = PHI (a_2, b_1);


 
   
jeff