[Bug target/18019] [4.0 Regression] -march=pentium4 generates word fetch instead of byte fetch

["roger at eyesopen dot com" <gcc-bugzilla at gcc dot gnu dot org>]

------- Additional Comments From roger at eyesopen dot com  2004-11-09 20:56 -------
I agree with Stuart :>

Although both of the patches he investigated will cure the problem, reverting
mine will generate a movzbl, whilst disabling the TARGET_PARTIAL_... bits will
generate a "movb".  As hinted in the original problem description, when
optimizing for size we ideally want the smaller "movb" (2 bytes vs. 3 bytes). 
But I still don't think disabling the TARGET_PARTIAL_... bits completely is
an ideal solution.  It would be better to take advantage of any alignment
information on the MEM to determine whether this transformation is safe, and
still benefit from this optimization when it is.

I'm also still not convinced that there aren't any non -Os cases where the
existing TARGET_PARTIAL_... code is incorrect without checking alignment.
Perhaps initially we should disable TARGET_PARTIAL_... only when optimizing
for size? I'm not convinced its perfect, but it would resolve this failure
and not hurt performance at -O2/-O3.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=18019