Re: [PATCH v2 2/4] LoongArch: Add ftint{,rm,rp}.{w,l}.{s,d} instructions

[Joseph Myers <joseph@codesourcery.com>]

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On Thu, 10 Nov 2022, Xi Ruoyao via Gcc-patches wrote:

> Joseph: can you confirm that -ftrapping-math allows floor and ceil to
> raise inexact exception?  The man page currently says:
> 
> The default is -ffp-int-builtin-inexact, allowing the exception to be
> raised, unless C2X or a later C standard is selected.  This option does 
>                                                        ^^^^^^^^^^^
> nothing unless -ftrapping-math is in effect.
> 
> To me it's not very clear that "this option" stands for -fno-fp-int-
> builtin-inexact or -ffp-int-builtin-inexact.

The -ftrapping-math option (which is on by default) means that we care 
about whether operations raise exceptions: they should raise exceptions if 
and only if the relevant standard permit them to do so.

The combination of -ftrapping-math with -fno-fp-int-builtin-inexact means 
the listed built-in functions must not raise "inexact".

If -fno-trapping-math is used, then we don't care about whether exceptions 
are raised or not (for any floating-point operations, not just those 
functions).  So given -fno-trapping-math, there is no difference between 
-fno-fp-int-builtin-inexact and -ffp-int-builtin-inexact.

If -ffp-int-builtin-inexact (default before C2X), we don't care about 
whether those functions raise "inexact" (but still care about other 
exceptions and exceptions for other operations, unless 
-fno-trapping-math).

-- 
Joseph S. Myers
joseph@codesourcery.com