[Bug target/49263] SH Target: underutilized "TST #imm, R0" instruction

["olegendo at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=49263

--- Comment #36 from Oleg Endo <olegendo at gcc dot gnu.org> ---
(In reply to Alexander Klepikov from comment #35)
> 
> As I understand, you meant the following (I added new functions at the end
> of file):
> 
> $ cat f.c
> #define ADDR 0xFFFF0000
> #define P ((unsigned char *)ADDR)
> #define FLAG 0x40
> #define S 7
> ....

Yes, that's what I meant, thanks.

Can you also compile for little endian, and most of all, use -O2 optimization
level.  Some optimizations are not done below -O2.

> 
> I choose that name because I wanted to disable dynamic shift instructions
> for all CPUs. I did not hope that it will affect SH-2E code in such way.
> 
> I can rewrite the patch so that it only affects CPUs that do not support
> dynamic shifts and disables library call for dynamic shifts. I'll do it
> anyway because I need it badly. How do you think, what name of option would
> be better: '-mdisable-dynshift-libcall' or '-mhw-shift'? Or if you want,
> please suggest another one. Thank you!

'-mdisable-dynshift-libcall' would be more appropriate for what it tries to do,
I think.  Although that is a whole different issue ... but what is it going to
do for real dynamic shifts on SH2?

What kind of code is it supposed to emit for things like

unsigned int dyn_shift (unsigned int x, unsigned int y)
{
  return x << (y & 31);
}