Le 18/09/2022 à 08:12, Richard Biener a écrit :
On Sat, Sep 17, 2022 at 9:33 PM Mikael Morin <morin-mik...@orange.fr> wrote:
Le 17/09/2022 à 19:03, Thomas Koenig via Fortran a écrit :
I have a concern about this part, though. My understanding at the
time was that it is not possible to clobber an individual array
element, but that this clobbers anything off the pointer that this
is based on.
Well, we need the middle-end guys to give a definitive answer on this
topic, but I think it would be a very penalizing limitation if that was
the case. I have assumed that the clobber spanned the value it was
applied on, neither more nor less, so just the array element in case of
array elements.
There is IL verification that the LHS of a CLOBBER is either
a declaration or a pointer dereference, no array or component
selection is allowed there. Now, nothing should go wrong here,
but we might eventually just drop those CLOBBERs or ICE if
we frontend hands us an "invalid" one.
Obviously I have assumed too much here; it's probably best to drop this
patch.
It is unfortunate as there is some desirable behavior within reach here.
The test shows that the patch permits the elimination of a useless
store. And IL verification doesn't seem that upset with it by the way.
Does *(&a[1]) count as a pointer dereference? Even in the original dump
it is already simplified to a straight a[1].
