Re: __sync_lock_test_and_set on ARM

["Phil Endecott" <spam_from_gcc_help_2 at chezphil dot org>]

David Daney wrote:
> There is nothing that says that __sync_compar_and_swap() cannot expand to a libcall.

> Ideally a GCC user would not have to write target specific assembly for 
> this.

If I just had one algorithm for my locking problem then, yes, that 
would be fine.  But as it happens I have two algorithms, one of which 
uses atomic compare-and-set and one of which uses atomic swap.  I want 
to use whichever maps best to the target architecture.  So I need to be 
able to distinguish between a builtin that expands to a couple of 
inline instructions and a builtin that expands to a library call.

If someone would like to add OS-specific builtins for the other atomic 
operations, that's fine, but please do something so that I can identify 
that they involve library or kernel calls (e.g. #define 
__SYNC_COMPARE_AND_SET_n=ASM vs. #define 
__SYNC_COMPARE_AND_SET_n=LIBRARY.)  But that looks like a lot more work 
than just adding one builtin for SWP, which is all that I need.


Phil.