rjmccall added a comment.
Thanks. Could you add some tests that `nontemporal` directives aren't
disturbed by either (1) nested `nontemporal` directives or (2) nested
directives of some other kind?
================
Comment at: clang/lib/CodeGen/CGExpr.cpp:3952
+ CGM.getOpenMPRuntime().isNontemporalDecl(Field)) ||
+ (!E->isArrow() && BaseLV.isNontemporal()))
+ LV.setNontemporal(/*Value=*/true);
----------------
ABataev wrote:
> rjmccall wrote:
> > ABataev wrote:
> > > ABataev wrote:
> > > > rjmccall wrote:
> > > > > Is the `!E->isArrow()` condition necessary here? Why not just
> > > > > propagate the non-temporality of the base?
> > > > >
> > > > > Similarly, what's the case in which the declaration is marked
> > > > > non-temporal and you *don't* want to trust that?
> > > > That's the main question. I try to mimic the behavior we currenty have
> > > > in the codegen. If the lvalue for the pointer is marked as nontemporal,
> > > > only loads/stores for the pointer itself are marked as nontemporal.
> > > > Operations with the memory it points to are not marked as nontemporal.
> > > > I'm trying to do the same. E.g., if have something like `a.b->c` and
> > > > `a` is nontemporal, then only `a.b = x;` must be marked as nontemporal,
> > > > but not `a.b->c = x;`
> > > > Similarly, what's the case in which the declaration is marked
> > > > non-temporal and you *don't* want to trust that?
> > >
> > > There is no such case. We can mark `this->member` as nontemporal or
> > > `declref`. The first check here checks if we have `this->member` marked
> > > as nontemporal, the second check just propagates the flag if the base is
> > > marked as nontemporal.
> > Okay. Then this should just be `(BaseLV.isNontemporal() ||
> > CGM.getOpenMPRuntime().isNontemporalDecl(Field))`.
> Still, `a->c` will be marked as nontemporal if `a` is nontemporal. Also, if
> we remove the check for the `CXXThis` in the condition, we can erroneously
> mark the instruction as nontemporal if we reference member of another base,
> which is nontemporal:
> ```
> struct S;
> extern S s;
> struct S {
> int a, b;
> void foo() {
> #pragma omp simd nontemporal(a)
> for (int i = 0; i < 10; ++i)
> s.a = 0; // Will be marked as nontemporal though it should not?
> }
> } s;
>
> ```
> Still, a->c will be marked as nontemporal if a is nontemporal.
No, the base LValue we build in this case will not be related to the LValue for
`a`; the pointer is loaded from that l-value, but its properties do not
propagate to the pointer, just like how `S * volatile s` doesn't mean that
`s->x` is `volatile`.
> Also, if we remove the check for the CXXThis in the condition, we can
> erroneously mark the instruction as nontemporal if we reference member of
> another base, which is nontemporal:
I see, this is specifically part of the semantics that the field only becomes
non-temporal for `this`. Okay, I accept that part of the original condition.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D71708/new/
https://reviews.llvm.org/D71708
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