- Compatible with Emscripten 1.38.46-upstream or later upstream.
- Refactors the Emscripten target spec to share code with other wasm
targets.
- Replaces the old incorrect wasm32 C call ABI with the correct one,
preserving the old one as wasm32_bindgen_compat for wasm-bindgen
compatibility.
- Updates the varargs ABI used by Emscripten and deletes the old one.
- Removes the obsolete wasm32-experimental-emscripten target.
- Uses EMCC_CFLAGS on CI to avoid the timeout problems with #63649.
- Refactors the Emscripten target spec to share code with other wasm
targets.
- Replaces the incorrect wasm32 C call ABI with the old asmjs
version, which is correct for both wasm32 and JS.
- Updates the varargs ABI used by Emscripten and deletes the old one.
- Removes the obsolete wasm32-experimental-emscripten target.
- Temporarily makes Emscripten targets use panic=abort by default
because supporting unwinding will require an LLVM patch.
Improve the documentation for std::hint::black_box.
The other day a colleague was reviewing some of my code which was using `black_box` to block constant propogation. There was a little confusion because the documentation kind of implies that `black_box` is only useful for dead code elimination, and only in benchmarking scenarios.
The docs currently say:
> A function that is opaque to the optimizer, to allow benchmarks to pretend to use outputs to assist in avoiding dead-code elimination.
Here is our discussion, in which I show (using godbolt) that a black box can also block constant propagation:
https://github.com/softdevteam/yk/pull/21#discussion_r302985038
This change makes the docstring for `black_box` a little more general, and while we are here, I've added an example (the same one from our discussion).
OK to go in?
This is duplicated in a few locations throughout the sysroot to work
around issues with not exporting a macro in libstd but still wanting it
available to sysroot crates to define blocks. Nowadays though we can
simply depend on the `cfg-if` crate on crates.io, allowing us to use it
from there!
This changes removes a cyclic dependency between the "test" and "libtest"
crates, where "libtest" depends on "test" for "black_box", but "test" depends on
"libtest" for everything else.
I've chosen the "hint" module because there seems to be enough consensus in the
discussion of RFC2360 that this module is where such an intrinsic would belong,
but this PR does not implement that RFC! (note: if that RFC ever gets merged,
the API, docs, etc. of this API will need to change).
For backwards compatibility reasons I've chosen to also keep the "test" feature
gate for these instead of adding a new feature gate. If we change the feature
gate, we'll potentially all benchmarks, and while that's something that we could
do, it seems unnecessary to do that now - if RFC2360 gets merged, we'll need to
do that anyways.
The pause instruction requires SSE2 but was being unconditionally used
on targets without it, resulting in undefined behavior.
This PR fixes that by only using the pause intrinsic if SSE2 is available.
It also removes the inline assembly which was not required since these
instructions are available in core::arch, and extends support of
the spin_loop hint to arm targets with the v6 feature which also
support the yield instruction.
Closes#59237 .
