[cfe-dev] [atomic] 32 bit bug fixed recently?

[Howard Hinnant]

Thanks David.  On i386, and using tip-of-trunk clang, all of libc++'s atomic tests pass.  Would you agree that we should mark:

http://llvm.org/bugs/show_bug.cgi?id=15457

as fixed by your work?

Howard

On Mar 9, 2013, at 4:53 AM, David Chisnall <David.Chisnall at cl.cam.ac.uk> wrote:

> Hi Howard,
> 
> I made a number of improvements to the clang C11 atomics support last weekend.  I intended to fix some poor performance on MIPS (and ARM, and anything else non-x86), but it turned out that we were generating invalid IR for a number of fairly simple operations.  I don't know if this is related.  There are almost certainly some more corner cases that don't work, and some fairly major issues:
> 
> 1) We don't yet properly understand that _Atomic(T) and T can have different in-memory representations (in particular, on most non-x86 architectures, we really want to ensure that _Atomic(short) and _Atomic(char) have zeroed padding so that we can do efficient atomic operations on them - this isn't really up to us, but is something that should appear in C11 supplements to various ABIs)
> 
> 2) We don't save and restore the floating point exception state around floating point atomic operations.  I'm tempted to say that anyone who thinks that atomic operation on a floating point value should step slowly away from the computer, but the standard does allow this...
> 
> David
> 
> On 8 Mar 2013, at 20:42, Howard Hinnant <hhinnant at apple.com> wrote:
> 
>> Does anyone recognize this bug report as something that's recently been fixed in clang?
>> 
>> http://llvm.org/bugs/show_bug.cgi?id=15457
>> 
>> It is a failure only on 32 bit architecture (I only tested i386).  And I can **not** reproduce it with tip-of-trunk clang, only with Apple LLVM version 4.2 (clang-425.1.16) (based on LLVM 3.2svn).
>> 
>> I'm hoping someone recognizes another bug report that I can just dup this one to.
>> 
>> Thanks,
>> Howard
>> 
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