[Bug optimization/14797] [tree-ssa] propagate constants back to PHI

[kazu at cs dot umass dot edu]

------- Additional Comments From kazu at cs dot umass dot edu  2004-03-31 15:32 -------
I don't know where to draw a line.  Even for the last example, i386
port converts the code to

b = a != 0;
b--;
b &= 500;
b += 201;

but this would be a nightmare on ports without setcc (like h8).

Maybe we could keep anything more complex than "c = a COND b" in the
if-then-else form (assuming we don't want to introduce
machine-dependent if-conversion pass at tree level).  If we don't want
to rely on rtl optimizers to do if-conversion, we could put a flag to
"if" to indicate that that's an if-conversion candidate (just like
tail-call flag) and then do the if-conversion at the expand time.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=14797