[Bug target/43892] PowerPC suboptimal "add with carry" optimization

["dje at gcc dot gnu dot org" <gcc-bugzilla@gcc.gnu.org>]

------- Comment #16 from dje at gcc dot gnu dot org  2010-05-27 01:37 -------
>> You have no patience, now do you?

> Sure I do. It is just that its been almost a month and from the
> description it sounded like an easy fix:
> "config/rs6000/rs6000.md would need to add a add<mode>cc expander"

No you do not have any patience; in fact, your comments are rather obnoxious,
such as: "its been almost a month".  If you do not know what you are talking
about, stop talking.  No, it is not an easy fix.  The high-level concept and
description is simple, the implementation is extremely complex and tedious.

>> even though it sounded that the
>> initial fix was easy(add<mode>cc expander)
> 
>> The fix will be a few thousand lines of patch.  Literally.

> Oops, just to add a cc expander?

Yes.  Again, if you do not know the complexity of what you are requesting, get
more information instead of acting annoyed that people are not jumping to solve
your problem.

It is not "just adding" a cc expander.  Do you even know what that means or
what it involves?  For the expander to be effective, the PowerPC port of GCC
needs to be taught to track the carry bit, which it currently does not.  *ALL*
patterns that produce instructions affecting the carry bit must be updated. 
One cannot add the pattern in isolation.

If you do not understand the implications of your request, then *ask* why it is
more complicated than you assumed.  There is no "simple" fix.  The only fix is
the ultimate fix: completely propagating the carry bit throughout the PowerPC
port.

You apparently have not read the documentation to understand the -mcpu= option
or the --with-cpu= configure option.  You are making a lot of incorrect
assumption and assertions, apparently without making any effort to gain some
knowledge before you start writing.  That really does not encourage anyone to
help you, especially when it requires a lot of work.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43892