[PATCH] handle bzero/bcopy in DSE and aliasing (PR 80933, 80934)

[Joseph Myers]

On Wed, 7 Jun 2017, Bernhard Reutner-Fischer wrote:

> It's like optimizing foo() to a random built-in but maybe that's just 
> me. If your libc provides a define to a standard function for these 
> under a compat knob then fine but otherwise you should fix that. 
> *shrug*. Joseph?

It's the usual thing of: if the -std option enables a function as built-in 
it can be assumed to have certain semantics if called (this does *not* 
mean it's appropriate to generate calls to it from code that called other 
functions, as the library might not have it at all; that's for the 
libc_has_function hook to specify).  Otherwise (-std=c11 etc. options) 
semantics cannot be assumed based on the name (they still can for 
__builtin_*) - but in principle it may be OK to assume semantics for a 
function whose name is reserved in the relevant C standard version, or if 
an explicit declaration came from a system header (which would generally 
be the case for e.g. -std=c99 -D_POSIX_C_SOURCE=whatever).

-- 
Joseph S. Myers
joseph@codesourcery.com