Re: [RFC] Introduce -finline-memset-loops

[Paul Koning <paulkoning@comcast.net>]

> On Jan 13, 2023, at 8:54 PM, Alexandre Oliva via Gcc-patches <gcc-patches@gcc.gnu.org> wrote:
> 
> Hello, Richard,
> 
> Thank you for the feedback.
> 
> On Jan 12, 2023, Richard Biener <richard.guenther@gmail.com> wrote:
> 
>> On Tue, Dec 27, 2022 at 5:12 AM Alexandre Oliva via Gcc-patches
>> <gcc-patches@gcc.gnu.org> wrote:
> 
>>> This patch extends the memset expansion to start with a loop, so as to
>>> still take advantage of known alignment even with long lengths, but
>>> without necessarily adding store blocks for every power of two.
> 
>> I wonder if that isn't better handled by targets via the setmem pattern,
> 
> That was indeed where I started, but then I found myself duplicating the
> logic in try_store_by_multiple_pieces on a per-target basis.
> 
> Target-specific code is great for tight optimizations, but the main
> purpose of this feature is not an optimization.  AFAICT it actually
> slows things down in general (due to code growth, and to conservative
> assumptions about alignment), 

I thought machinery like the memcpy patterns have as one of their benefits the ability to find the alignment of their operands and from that optimize things.  So I don't understand why you'd say "conservative".

	paul