Turn nonzeroing move hints back off by default.
Works around bugs injected by PR #26173.
* (@pnkfelix is unavailable in the short-term (i.e. for the next week) to fix them.)
* When the bugs are fixed, we will turn nonzeroing move hints back on by default.
Fix#27401
This is a temporary workaround for the bugs that have been found in
the implementation of PR #26173.
* pnkfelix is unavailable in the short-term (i.e. for the next week) to fix them.
* When the bugs are fixed, we will turn this back on by default.
(If you want to play with the known-to-be-buggy optimization in the
meantime, you can opt-back in via the debugging option that this
commit is toggling.)
This ended up being a bigger refactoring than I thought, as I also cleaned a few ugly points in rustc. There are still a few areas that need improvements.
Performance numbers:
```
Before:
572.70user 5.52system 7:33.21elapsed 127%CPU (0avgtext+0avgdata 1173368maxresident)k
llvm-time: 385.858
After:
545.27user 5.49system 7:10.22elapsed 128%CPU (0avgtext+0avgdata 1145348maxresident)k
llvm-time: 387.119
```
A good 5% perf improvement. Note that after this patch >70% of the time is spent in LLVM - Amdahl's law is in full effect.
Passes make check locally.
r? @nikomatsakis
This search happens a lot! Locally, compiling hyper sees the following improvements:
before
real 0m30.843s
user 0m51.644s
sys 0m2.128s
real 0m30.164s
user 0m53.320s
sys 0m2.208s
after
real 0m28.438s
user 0m51.076s
sys 0m2.276s
real 0m28.612s
user 0m51.560s
sys 0m2.192s
This search happens a lot! Locally, compiling hyper sees the following improvements:
before
real 0m30.843s
user 0m51.644s
sys 0m2.128s
real 0m30.164s
user 0m53.320s
sys 0m2.208s
after
real 0m28.438s
user 0m51.076s
sys 0m2.276s
real 0m28.612s
user 0m51.560s
sys 0m2.192s
I got a bit confused reading the guide over why all of a sudden there was an asterisk in the code. I was explained what it was there for in the IRC, and I think it should added it to the docs to prevent any further confusion!
This pull request implements the functionality for [RFC 873](https://github.com/rust-lang/rfcs/blob/master/text/0873-type-macros.md). This is currently just an update of @freebroccolo's branch from January, the corresponding commits are linked in each commit message.
@nikomatsakis and I had talked about updating the macro language to support a lifetime fragment specifier, and it is possible to do that work on this branch as well. If so we can (collectively) talk about it next week during the pre-RustCamp work week.
In Section 3.2, TARPL says that "standard allocators (including jemalloc, the one used by default in Rust) generally consider passing in 0 for the size of an allocation as Undefined Behaviour."
However, the C standard and jemalloc manual says allocating zero bytes
should succeed:
- C11 7.22.3 paragraph 1: "If the size of the space requested is zero, the behavior is implementation-defined: either a null pointer is returned, or the behavior is as if the size were some nonzero value, except that the returned pointer shall not be used to access an object."
- [jemalloc manual](http://www.freebsd.org/cgi/man.cgi?query=jemalloc&sektion=3): "The malloc and calloc functions return a pointer to the allocated memory if successful; otherwise a NULL pointer is returned and errno is set to ENOMEM."
+ Note that the description for `allocm` says "Behavior is undefined if size is 0," but it is an experimental API.
r? @Gankro
