PowerPC : GCC2 optimises better than GCC4???

[Andrew Haley]

On 01/04/2010 12:07 PM, Jakub Jelinek wrote:
> On Mon, Jan 04, 2010 at 12:18:50PM +0100, Steven Bosscher wrote:
>>On Mon, Jan 4, 2010 at 12:02 PM, Andrew Haley <aph@redhat.com> wrote:
>>> This optimization is done by the first RTL cse pass.  I can't understand
>>> why it's not being done for your target.  I guess this will need a
>>> powerpc expert.
>>
>> Known bug, see http://gcc.gnu.org/PR22141
> 
> That's unrelated.  PR22141 is about (lack of) merging of adjacent stores of
> constant values into memory, but there are no memory stores involved here,
> everything is in registers, so PR22141 patch will make zero difference here.
> 
> IMHO we really should have some late tree pass that converts adjacent
> bitfield operations into integral operations on non-bitfields (likely with
> alias set of the whole containing aggregate), as at the RTL level many cases
> are simply too many instructions for combine etc. to optimize them properly,
> while at the tree level it could be simpler.

Yabbut, how come RTL cse can handle it in x86_64, but PPC not?

Andrew.