[PATCH] LoongArch: Optimize math barriers

[dengjianbo]

  On 5/8/26 5:29 PM, Xi Ruoyao wrote:
> On Thu, 2026-05-07 at 17:30 +0800, dengjianbo wrote:
>> Yes, unnecessary moves can occur if the value is already in a general
>> reg. For example, when invoking math_opt_barrier with fixed-point
>> parameters. However, in glibc, these two macros are invoked with
>> floating-point parameters, and I didn’t find the unnecessary moves
>> being generated. For other architectures, aarch64 and s390 also do
>> not include the 'r' constraint.
>>
>> For gcc part, to my understanding, when 'fr' is present, GCC selects the
>> union of FP_REGS and GR_REGS as the destination register class, which is
>> initialized to GR_REGS. Then compute the cost of choosing different
>> register classes, choosing GR_REGS incurs no extra cost, while choosing
>> FP_REGS adds an extra move cost. I am not sure if it's a strategy here.
> 
> Where does this issue manifest (i.e. in which glibc source file)?  I'll
> try to reduce a test case from that.  To me this seems a compiler bug
> too.
>>
> 
One example is the xflow function, compiler generates the unnecessary 
moves for this function, the source file is 
sysdeps/ieee754/dbl-64/math_err.c．