rjmccall added inline comments.
================
Comment at: clang/lib/Sema/SemaExpr.cpp:5917
if (auto *BE = dyn_cast<BlockExpr>(Arg->IgnoreParenNoopCasts(Context)))
BE->getBlockDecl()->setDoesNotEscape();
----------------
ahatanak wrote:
> rjmccall wrote:
> > We need to be checking that the parameter type is a block pointer type. A
> > parameter of a type like `id` or `void*` does not have the enhanced
> > semantics of `noescape` for blocks.
> >
> > The inevitable weird C++ test case is:
> >
> > ```
> > struct NoescapeCtor {
> > NoescapeCtor(__attribute__((noescape)) void (^)());
> > };
> > struct EscapeCtor {
> > EscapeCtor(void (^)());
> > };
> >
> > void helper1(NoescapeCtor a);
> > void test1() { helper1(^{}); } // <- should be noescape
> >
> > void helper2(NoescapeCtor &&a);
> > void test2() { helper2(^{}); } // <- should be noescape
> >
> > void helper3(__attribute__((noescape)) EscapeCtor &&a);
> > void test3() { helper3(^{}); } // <- should not be noescape
> > ```
> >
> > You should probably also test that calls to function templates behave
> > according to the instantiated type of the parameter. I expect that that
> > should just fall out from this implementation, which I think only triggers
> > on non-dependent calls.
> I understand why the blocks should or shouldn't be `noescape` in the C++
> example, but I'm not sure I understand the comment about `id` and `void*`.
>
> Do you mean the `DoesNotEscape` bit shouldn't be set in the following example?
>
> ```
> void helper(__attribute__((noescape)) id);
>
> void test() {
> S s;
> helper(^{ (void)s; });
> }
> ```
The [noescape
documentation](https://clang.llvm.org/docs/AttributeReference.html#id357) says:
> Additionally, when the parameter is a block pointer, the same restriction
> applies to copies of the block.
That's the restriction that makes the `noescape` block optimization sound, and
it doesn't apply when the parameter does not have block pointer type. So yes,
`DoesNotEscape` shouldn't be set in that example.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D101097/new/
https://reviews.llvm.org/D101097
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