JonChesterfield added a comment.
I've continued thinking about / experimenting with this. Curiously - `X x;` and
`X x{};` are considered distinct by clang. The current patch will only accept
the former. I'll add some tests for that.
I think there's a reasonable chance that the developers who want to elide the
runtime cost of zero initialising will usually also want to avoid dynamic
initialisation. That suggests we could accept only trivially default
constructible classes, where the undef initializer is correct in that one
cannot determine whether a no-op constructor actually ran or not. If we go with
that, then the more complicated question of exactly how this should interact
with user-controlled disabling of dynamic initialization can be postponed until
that feature is introduced. This patch is then reasonably self contained.
This patch is strongly related to the linker script approach, or equivalent
asm. It's target-dependent how the uninitialised data gets represented, e.g.
x64 will put it in bss anyway. Opencl's __local is similarly uninitialised, and
gets annotated with an address space that maps onto magic in llc and/or the
loader.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D74361/new/
https://reviews.llvm.org/D74361
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