[libgcc] Protect __TMC_END__ - __TMC_LIST__ == 0

[libgcc] Protect __TMC_END__ - __TMC_LIST__ == 0

[Marc Glisse]

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Hello,

some optimization patch I was working on simplified __TMC_END__ - 
__TMC_LIST__ == 0 to false, which is not wanted (I assume that's why it 
wasn't written __TMC_END__ == __TMC_LIST__ in the first place).

Bootstrap+regtest on powerpc64le-unknown-linux-gnu.

2016-10-27  Marc Glisse  <marc.glisse@inria.fr>

 	PR libgcc/77813
 	* crtstuff.c (deregister_tm_clones, register_tm_clones): Hide
 	__TMC_END__ behind a passthrough asm.

-- 
Marc Glisse

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Index: libgcc/crtstuff.c
===================================================================
--- libgcc/crtstuff.c	(revision 241611)
+++ libgcc/crtstuff.c	(working copy)
@@ -273,41 +273,47 @@ STATIC func_ptr __TMC_LIST__[]
 # ifdef HAVE_GAS_HIDDEN
 extern func_ptr __TMC_END__[] __attribute__((__visibility__ ("hidden")));
 # endif
 
 static inline void
 deregister_tm_clones (void)
 {
   void (*fn) (void *);
 
 #ifdef HAVE_GAS_HIDDEN
-  if (__TMC_END__ - __TMC_LIST__ == 0)
+  func_ptr *end = __TMC_END__;
+  // Do not optimize the comparison to false.
+  __asm ("" : "+g" (end));
+  if (__TMC_LIST__ == end)
     return;
 #else
   if (__TMC_LIST__[0] == NULL)
     return;
 #endif
 
   fn = _ITM_deregisterTMCloneTable;
   __asm ("" : "+r" (fn));
   if (fn)
     fn (__TMC_LIST__);
 }
 
 static inline void
 register_tm_clones (void)
 {
   void (*fn) (void *, size_t);
   size_t size;
 
 #ifdef HAVE_GAS_HIDDEN
-  size = (__TMC_END__ - __TMC_LIST__) / 2;
+  func_ptr *end = __TMC_END__;
+  // Do not optimize the comparison to false.
+  __asm ("" : "+g" (end));
+  size = (end - __TMC_LIST__) / 2;
 #else
   for (size = 0; __TMC_LIST__[size * 2] != NULL; size++)
     continue;
 #endif
   if (size == 0)
     return;
 
   fn = _ITM_registerTMCloneTable;
   __asm ("" : "+r" (fn));
   if (fn)

Re: [libgcc] Protect __TMC_END__ - __TMC_LIST__ == 0

[Marc Glisse]

Ping https://gcc.gnu.org/ml/gcc-patches/2016-10/msg02220.html

On Thu, 27 Oct 2016, Marc Glisse wrote:

> Hello,
>
> some optimization patch I was working on simplified __TMC_END__ - 
> __TMC_LIST__ == 0 to false, which is not wanted (I assume that's why it 
> wasn't written __TMC_END__ == __TMC_LIST__ in the first place).
>
> Bootstrap+regtest on powerpc64le-unknown-linux-gnu.
>
> 2016-10-27  Marc Glisse  <marc.glisse@inria.fr>
>
> 	PR libgcc/77813
> 	* crtstuff.c (deregister_tm_clones, register_tm_clones): Hide
> 	__TMC_END__ behind a passthrough asm.

-- 
Marc Glisse

Re: [libgcc] Protect __TMC_END__ - __TMC_LIST__ == 0

[Andrew Pinski]

On Fri, Nov 4, 2016 at 7:08 AM, Marc Glisse <marc.glisse@inria.fr> wrote:
> Ping https://gcc.gnu.org/ml/gcc-patches/2016-10/msg02220.html

I think this is obvious.

Thanks,
Andrew

>
>
> On Thu, 27 Oct 2016, Marc Glisse wrote:
>
>> Hello,
>>
>> some optimization patch I was working on simplified __TMC_END__ -
>> __TMC_LIST__ == 0 to false, which is not wanted (I assume that's why it
>> wasn't written __TMC_END__ == __TMC_LIST__ in the first place).
>>
>> Bootstrap+regtest on powerpc64le-unknown-linux-gnu.
>>
>> 2016-10-27  Marc Glisse  <marc.glisse@inria.fr>
>>
>>         PR libgcc/77813
>>         * crtstuff.c (deregister_tm_clones, register_tm_clones): Hide
>>         __TMC_END__ behind a passthrough asm.
>
>
> --
> Marc Glisse

Re: [libgcc] Protect __TMC_END__ - __TMC_LIST__ == 0

[Marc Glisse]

On Fri, 4 Nov 2016, Andrew Pinski wrote:

> On Fri, Nov 4, 2016 at 7:08 AM, Marc Glisse <marc.glisse@inria.fr> wrote:
>> Ping https://gcc.gnu.org/ml/gcc-patches/2016-10/msg02220.html
>
> I think this is obvious.

Ok, I've committed it.

-- 
Marc Glisse