rjmccall added inline comments.
================
Comment at: lib/CodeGen/CGBlocks.cpp:1682
+ if (IsCopyHelper && Ctx.getBlockVarCopyInits(Var).CanThrow)
+ Name += "c";
+ }
----------------
ahatanak wrote:
> rjmccall wrote:
> > I don't think you need to add `d` to the name of a copy helper. It's a bit
> > weird, but while copying a `__block` variable can cause its copy helper to
> > run, destroying it immediately afterwards can never cause its destroy
> > helper to run. That's because a newly-copied `__block` variable always has
> > a reference count of 2: the new reference in the copy and the forwarding
> > reference from the original.
> >
> > I think that means you can just add a single letter which specifies whether
> > the corresponding `__block` variable operation is known to be able to throw.
> I added 'd' to the name of the copy helper functions only because IRGen
> generates different code depending on whether the destructor can throw or not.
>
> For example, if I compile the following code with -DTHROWS, IRGen uses
> 'invoke' (which jumps to the terminate block) for the calls to
> `_Block_object_dispose` on the EH path whereas it uses 'call' if the
> destructor doesn't throw.
>
> ```
> struct S {
> S();
> #ifdef THROWS
> ~S() noexcept(false);
> #else
> ~S() noexcept(true);
> #endif
> S(const S &);
> int a;
> };
>
> void test() {
> __block S s0, s1, s2;
> ^{ (void)s0, (void)s1; (void)s2; };
> }
> ```
>
> It seems like IRGen doesn't have to use 'invoke' when emitting a call to
> `_Block_object_dispose` even when the class has a destructor that can throw,
> if I understood your explanation correctly?
Right. It's specifically only true when unwinding after a copy, which is very
atypical for C++ code, but nonetheless it's true. We should make the call
`nounwind` in these situations and leave a comment explaining why. Did my
explanation make any sense?
================
Comment at: lib/CodeGen/CGBlocks.cpp:1688
+ if (F == BLOCK_FIELD_IS_BLOCK)
+ Name += "b";
+ }
----------------
ahatanak wrote:
> rjmccall wrote:
> > Why `rb` for a captured block instead of some single-letter thing? You
> > don't need to emulate the structure of the flags here.
> I can use a single letter here, but I'm already using 'b' for byref captures.
> Perhaps I can use 'o' for non-arc objects, instead of 'r', and use 'r' for
> byref?
That seems reasonable.
Repository:
rC Clang
https://reviews.llvm.org/D50152
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