[llvm-commits] [llvm-gcc-4.2] r46589 - /llvm-gcc-4.2/trunk/gcc/llvm-convert.cpp

[Dale Johannesen]

On Jan 30, 2008, at 5:13 PM, Dale Johannesen wrote:

>
> On Jan 30, 2008, at 5:05 PM, Devang Patel wrote:
>
>> handle_used_attribute() sets DECL_PRESERVE_P bit, so what am I  
>> missing ?
>
> It was not set in the example in gcc.dg/tree-used.c.    I'll step  
> through and figure out why, agree it looks like it ought to be.

In that example there is a declaration with __attribute__((used)),  
followed by a definition without it.  merge_decls clobbers the  
PRESERVE bit when it merges the two nodes gcc constructs.   The  
DECL_USED bit is not clobbered, which is enough to cause the function  
to be emitted with non-llvm-gcc but not with llvm-gcc, which is enough  
to get the test to pass.   But, the no_dead_strip command is  
incorrectly dropped in the non-llvm-gcc version as well.  So I've  
stumbled into a latent gcc bug, although not one that causes any  
testsuite failures AFAICT.
(The attributes list is merged correctly in merge_decls, so my patch  
seems to be an improvement.   However, there's another case in my  
example, where a definition without attribute((used)) is followed by a  
declaration with attribute((used)).  For that, the USED bit gets set  
and is good enough for gcc to emit the body, as before, but both  
compilers drop the no_dead_strip:  a bug.  Unfortunately the USED bit  
is not good enough for llvm: llvm drops the second definition if you  
run llvm-as | opt | llc instead of using llvm-gcc.  So there's still a  
bug here that may matter.)
Good catch, thanks Devang.

>> On Jan 30, 2008, at 5:00 PM, Dale Johannesen wrote:
>>
>>> Author: johannes
>>> Date: Wed Jan 30 19:00:20 2008
>>> New Revision: 46589
>>>
>>> URL: http://llvm.org/viewvc/llvm-project?rev=46589&view=rev
>>> Log:
>>> The 'used' attribute is not stored where llvm-convert
>>> thought it was.
>>>
>>>
>>> Modified:
>>>  llvm-gcc-4.2/trunk/gcc/llvm-convert.cpp
>>>
>>> Modified: llvm-gcc-4.2/trunk/gcc/llvm-convert.cpp
>>> URL: http://llvm.org/viewvc/llvm-project/llvm-gcc-4.2/trunk/gcc/llvm-convert.cpp?rev=46589&r1=46588&r2=46589&view=diff
>>>
>>> =
>>> =
>>> =
>>> =
>>> =
>>> =
>>> =
>>> =
>>> = 
>>> = 
>>> ====================================================================
>>> --- llvm-gcc-4.2/trunk/gcc/llvm-convert.cpp (original)
>>> +++ llvm-gcc-4.2/trunk/gcc/llvm-convert.cpp Wed Jan 30 19:00:20 2008
>>> @@ -633,7 +633,7 @@
>>>   Fn->setSection(TREE_STRING_POINTER(DECL_SECTION_NAME(FnDecl)));
>>>
>>> // Handle used Functions
>>> -  if (DECL_PRESERVE_P (FnDecl))
>>> +  if (lookup_attribute ("used", DECL_ATTRIBUTES (FnDecl)))
>>>   AttributeUsedGlobals.insert(Fn);
>>>
>>> // Handle noinline Functions
>>>
>>>
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>>
>> -
>> Devang
>>
>>
>>
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>