Fixing inline expansion of overlapping memmove and non-overlapping memcpy

[Michael Matz]

Hi,

On Tue, 14 May 2019, Aaron Sawdey wrote:

> memcpy -> expand with movmem pattern
> memmove (no overlap) -> transform to memcpy -> expand with movmem pattern
> memmove (overlap) -> remains memmove -> glibc call
...
> However in builtins.c expand_builtin_memmove() does not actually do the 
> expansion using the memmove pattern.

Because it can't: the movmem pattern is not defined to require handling 
overlaps, and hence can't be used for any possibly overlapping 
memmove.  (So, in a way the pattern is misnamed and should probably have 
been called cpymem from the beginning, alas there we are).

> So here's my proposed set of fixes:
>  * Add new optab entries for nonoverlapping_memcpy and overlapping_memmove
>    cases.

Wouldn't it be nicer to rename the current movmem pattern to cpymem 
wholesale for all ports (i.e. roughly a big s/movmem/cpymem/ over the 
whole tree) and then introduce a new optional movmem pattern with 
overlapping semantics?


Ciao,
Michael.