[Bug middle-end/32667] block copy with exact overlap is expanded as memcpy

[bugdal at aerifal dot cx]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=32667

Rich Felker <bugdal at aerifal dot cx> changed:

           What    |Removed                     |Added
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                 CC|                            |bugdal at aerifal dot cx

--- Comment #24 from Rich Felker <bugdal at aerifal dot cx> ---
If the copy is such that gcc is happy to emit an external call to memcpy for
it, there is no significant size or performance cost to emitting a branch
checking for equality before making the call, and performing this branch would
greatly optimize the (maybe rare in the caller, maybe not) case of
self-assignment!

On the other hand, expecting the libc memcpy to make this check greatly
pessimizes every reasonable small use of memcpy with a gratuitous branch for
what is undefined behavior and should never appear in any valid program.

Fix it on the compiler side please.