[PATCH] Prefer mempcpy to memcpy on x86_64 target (PR middle-end/81657).

[H.J. Lu]

On Wed, Mar 14, 2018 at 5:54 AM, Martin Liška <mliska@suse.cz> wrote:
> On 03/13/2018 04:23 PM, Jakub Jelinek wrote:
>> On Tue, Mar 13, 2018 at 04:19:21PM +0100, Martin Liška wrote:
>>>> Yes, see e.g. TARGET_LIBC_HAS_FUNCTION target hook,
>>>> where in particular linux_libc_has_function deals with various C libraries.
>>>> Of course, in this case you need another target hook, that is dependent both
>>>> on the target backend and C library.
>>>>
>>>> It would be nice to make the target hook a little bit more generic as well,
>>>> e.g. pass it enum builtin_function and query if it is fast, slow or
>>>> unknown, or even some kind of cost, where the caller could ask for cost of
>>>> BUILT_IN_MEMCPY and BUILT_IN_MEMPCPY and decide based on the relative costs.
>>>
>>> Let me start with simple return enum value of FAST,SLOW,UNKNOWN. I've added new hook
>>> definition to gcc/config/gnu-user.h that will point to gnu_libc_function_implementation.
>>> I would like to implement the function in gcc/targhooks.c, but I don't know how to
>>> make ifdef according to target?
>>
>> Put there just the default implementation (everything is UNKNOWN?).
>>
>>> One another issue is that built_in_function is enum defined in tree.h. Thus I'll replace the
>>> callback argument with int, that will be casted. One last issue: am I right that I'll have to define
>>> TARGET_LIBC_FUNCTION_IMPLEMENTATION in each config file (similar to no_c99_libc_has_function)?
>>
>> And define the i386/x86_64 glibc one in config/i386/*.h, check there
>> OPTION_GLIBC and only in that case return something other than UNKNOWN.
>>
>> And redefine TARGET_LIBC_FUNCTION_IMPLEMENTATION only in that case.
>>
>>       Jakub
>>
>
> Hi.
>
> I'm sending V2 that can survive bootstrap and regression tests on both x86_64 and ppc64le.
>
> Martin

diff --git a/gcc/testsuite/gcc.c-torture/execute/builtins/mempcpy.c
b/gcc/testsuite/gcc.c-torture/execute/builtins/mempcpy.c
index d82e2232d7b..91e1c87f83f 100644
--- a/gcc/testsuite/gcc.c-torture/execute/builtins/mempcpy.c
+++ b/gcc/testsuite/gcc.c-torture/execute/builtins/mempcpy.c
@@ -62,7 +62,7 @@ main_test (void)
   mempcpy (p + 5, s3, 1);
   if (memcmp (p, "ABCDEFg", 8))
     abort ();
-  mempcpy (p + 6, s1 + 1, l1);
+  memcpy (p + 6, s1 + 1, l1);
   if (memcmp (p, "ABCDEF2", 8))
     abort ();
 }

This is a mempcpy test.  Why is mempcpy changed to memcpy?

-- 
H.J.