Re: [PATCH v2] LoongArch: testsuite:Added additional vectorization "-mlsx" option.

[chenxiaolong <chenxiaolong@loongson.cn>]

At 14:42 +0800 on the first day of 2024-01-15, Xi Ruoyao wrote：
> On Mon, 2024-01-15 at 14:32 +0800, YunQiang Su wrote:
> > Xi Ruoyao <xry111@xry111.site> wrote at 12:11pm on Monday, January
> > 15, 2024：
> > > On Mon, 2024-01-15 at 09:29 +0800, chenxiaolong wrote:
> > > > At 21:13 +0800 on Saturday, 2024-01-13, Xi Ruoyao wrote：
> > > > > At 15:28 +0800 on Saturday 2024-01-13, chenxiaolong wrote：
> > > > > > gcc/testsuite/ChangeLog:
> > > > > > 
> > > > > >   * gcc.dg/pr104992.c: Added additional "-mlsx" compilation
> > > > > > options.
> > > > > >   * gcc.dg/signbit-2.c: Dito.
> > > > > >   * gcc.dg/tree-ssa/scev-16.c: Dito.
> > > > > >   * gfortran.dg/graphite/vect-pr40979.f90: Dito.
> > > > > >   * gfortran.dg/vect/fast-math-mgrid-resid.f: Dito.
> > > > > 
> > > > > I don't feel it right about the changes to pr104992.c and
> > > > > scev-16.c
> > > > > because no other architectures add special options there. 
> > > > > Why are we
> > > > > so special?
> > > > Because on the LoongArch architecture, GCC requires the
> > > > addition of
> > > > vectorization options in order to generate vector code. Use the
> > > > check_effective_target_vect_cmdline_needed command in the
> > > > lib/target-
> > > > supports.exp file to set whether the command line option is
> > > > needed to
> > > > enable vectorizations. For example, ia64,x86,aarch64, and riscv
> > > > architectures, vectorization is enabled by default.
> > > 
> > > But no.  The default baseline of 32-bit x86 is i686, which is
> > > basically
> > > a Pentium III launched in 1999 without any vector instructions.
> > > 
> > > We are still missing something here.
> > > 
> > There is a line
> >      #define vector __attribute__((vector_size(4*sizeof(int))))
> > I guess it is the syntax needs to be supported.
> 
> This is always supported.  If the target does not have vector
> instructions GCC will just expand vector arithmetic as a loop.
> 
> Maybe we should just move this test into gcc.dg/vect where the
> framework
> automatically add options like -mlsx or -msse2?
> 

The "-mlsx" option is turned on by default after vectorization testing
is turned on. However, the use of dg-options in some files resets the
compilation options for testing this file. Therefore, to detect
vectorization on LoongArch, it is necessary to add an additional "-
mlsx" option.