Re: [RFC] test builtin ratio for loop distribution

[Alexandre Oliva <oliva@adacore.com>]

On Jan 27, 2021, Richard Biener <richard.guenther@gmail.com> wrote:

> That said, rather than not transforming the loop as you do I'd
> say we want to re-inline small copies more forcefully during
> loop distribution code-gen so we turn a loop that sets
> 3 'short int' to zero into a 'int' store and a 'short' store for example
> (we have more code-size leeway here because we formerly had
> a loop).

Ok, that makes sense to me, if there's a chance of growing the access
stride.

> Since you don't add a testcase

Uhh, sorry, I mentioned TFmode emulation calls, but I wasn't explicit I
meant the soft-fp ones from libgcc.

./xgcc -B./ -O2 $srcdir/libgcc/soft-fp/fixtfdi.c \
  -I$srcdir/libgcc/config/riscv -I$srcdir/include \
  -S -o - | grep memset

> I can't see whether the actual case would be fixed by setting SSA
> pointer alignment on the memset arguments

The dest pointer alignment is known at the builtin expansion time,
that's not a problem.  What isn't known (*) is that the length is a
multiple of the word size: what gets to the expander is that it's
between 4 and 12 bytes (targeting 32-bit risc-v), but not that it's
either 4, 8 or 12.  Coming up with an efficient inline expansion becomes
a bit of a challenge without that extra knowledge.


(*) at least before my related patch for get_nonzero_bits
https://gcc.gnu.org/pipermail/gcc-patches/2021-January/564344.html

-- 
Alexandre Oliva, happy hacker  https://FSFLA.org/blogs/lxo/
   Free Software Activist         GNU Toolchain Engineer
        Vim, Vi, Voltei pro Emacs -- GNUlius Caesar