Re: [PATCH] don't generate long nops on i686 (only when -march=[intel])

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Thu, Aug 5, 2010 at 2:04 PM, Quentin Neill
<quentin.neill.gnu@gmail.com> wrote:
> On Mon, Aug 2, 2010 at 7:12 PM, H.J. Lu <hjl.tools@gmail.com> wrote:
>> On Mon, Aug 2, 2010 at 4:19 PM, Quentin Neill
>> <quentin.neill.gnu@gmail.com> wrote:
>>> On Tue, Jul 13, 2010 at 8:33 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
>>>> On Tue, Jul 13, 2010 at 5:59 AM, Kyle McMartin <kyle@mcmartin.ca> wrote:
>>>>> From: Kyle McMartin <kyle@redhat.com>
>>>>>
>>>>> Hi,
>>>>>
>>>>> In Fedora, glibc started building itself with -march=i686 flags to
>>>>> binutils as an "optimization." This exposes issues on the Geode, which
>>>>> is i686, but for long nops, since they are apparently not an architected
>>>>> part of the i686 ISA.
>>>>>
>>>>> Clarify this by only enabling long nops if we're generating 64-bit code
>>>>> (as far as I can tell, all x86_64 cpus support this) or explicitly
>>>>> generating code for the pentiumpro and above.
>>>>>
>>>>> Using this patch prevents people from overambitiously optimizing and
>>>>> breaking the Geode.
>>>>>
>>>>> Signed-off-by: Kyle McMartin <kyle@redhat.com>
>>>>
>>>> There is no ChangeLog. Please add CpuNop to i386-opc.h and use it
>>>> to determine when to generate nops.
>>>>
>>>> Thanks.
>>>
>>> Kyle, I was working on a similar patch. ?Here it is for previewing.
>>>
>>> It has a ChangeLog entry but without test cases. ?I will post with the
>>> test cases as soon as I get a clean "make check" .
>>
>> + ?{ STRING_COMMA_LEN (".Nop"), PROCESSOR_UNKNOWN,
>> + ? ?CPU_NOP_FLAGS, 0 },
>> + ?{ STRING_COMMA_LEN (".noNop"), PROCESSOR_UNKNOWN,
>> + ? ?CPU_NOP_FLAGS, 0 },
>>
>> All the others use lower case. Please use ".nop". ?I don't think ".noNop"
>> is correct since it is treated the same as ".nop". ?Please leave it out. ?We
>> can figure something else out later if we really need to turn off NOP.
>>
>> --
>> H.J.
>
> The following patch adds a ".nop" cpu subarch with testcases, to
> control generation of alignment code with nops.
>
> It changes the alignment code generated by -mtune=i686 to not include
> "nopl", by leaving the CpuNop capability out of the CPU_I686_FLAGS.
>
> It passes make -k check on x86.
>

OK.  Thanks.


-- 
H.J.