Hi Mikael,
Am 21.09.22 um 20:56 schrieb Mikael Morin:
Le 21/09/2022 à 11:57, Thomas Koenig a écrit :
Hi Harald,
I think I understand much of what is said, but I feel that I do
not really understand what *clobber* means for the different
beasts we are discussing (although I have an impression of what
it means for a scalar object).
More seriously: My understanding of a clobber it is a hint to
the middle end that the value in question will not be used,
and that operations leading to this value can be removed,
unless they are used otherwise.
My understanding is that "clobber" means "overwrite with garbage" for
all the beasts we have been discussing, which translates to nothing in
the final code, but can be used by the optimizers as Thomas said.
This is a bit off-topic but clobbers model registers having their values
changed unpredictably or by ways unknown to the compiler, in the backend
code, or in inline assembly statements.
Here is an excerpt from rtl.texi:
@item (clobber @var{x})
Represents the storing or possible storing of an unpredictable,
undescribed value into @var{x}
ah, I missed that file. I only found references to assembly,
and references to registers etc. were not really helpful here.
It also says:
> If @var{x} is @code{(mem:BLK (const_int 0))} or
> @code{(mem:BLK (scratch))}, it means that all memory
> locations must be presumed clobbered. ...
so this goes into the direction I was thinking of.
I Hope it helps.
