Passing CompAllocator objects by value is advantageous because it no longer needs to be dynamically allocated and cached. CompAllocator instances can now be freely created, copied and stored, which makes adding new CompMemKind values easier.
Together with other cleanup this also improves memory allocation performance by removing some extra levels of indirection that were previously required - jitstd::allocator had a pointer to CompAllocator, CompAllocator had a pointer to Compiler and Compiler finally had a pointer to ArenaAllocator. Without MEASURE_MEM_ALLOC enabled, both jitstd::allocator and CompAllocator now just contain a pointer to ArenaAllocator. When MEASURE_MEM_ALLOC is enabled CompAllocator also contains a pointer but to a MemStatsAllocator object that holds the relevant memory kind. This way CompAllocator is always pointer sized so that enabling MEASURE_MEM_ALLOC does not result in increased memory usage due to objects that store a CompAllocator instance.
In order to implement this, 2 additional signficant changes have been made:
* MemStats has been moved to ArenaAllocator, it's after all the allocator's job to maintain statistics. This also fixes some issues related to memory statistics, such as not tracking the memory allocated by the inlinee compiler (since that one used its own MemStats instance).
* Extract the arena page pooling logic out of the allocator. It doesn't make sense to pool an allocator, it has very little state that can actually be reused and everyting else (including MemStats) needs to be reset on reuse. What really needs to be pooled is just a page of memory.
Since this was touching allocation code the opportunity has been used to perform additional cleanup:
* Remove unnecessary LSRA ListElementAllocator
* Remove compGetMem and compGetMemArray
* Make CompAllocator and HostAllocator more like the std allocator
* Update HashTable to use CompAllocator
* Update ArrayStack to use CompAllocator
* Move CompAllocator & friends to alloc.h
Commit migrated from c2baf04cd2
GitHub recently changed how atx headings (beginning with `#`) are
rendered. A space is now required between `#` and the following text
for the heading to be recognized.
Update headings in the docs to match the expected format.
See https://github.github.com/gfm/#atx-headings
Commit migrated from 765f28934d
Add a note to the jit coding conventions that jit-format changes supersede
the conventions in the doc. Add a link to jit-format's documentation.
Commit migrated from 66f4808f97
On Linux the casing of environment variables matters, the documentation
commonly had the wrong casing for COMPlus_ which is misleading.
Commit migrated from 6d98d1711c
As raised in dotnet/coreclr#1075 by @akoeplinger, the Documentation folder's file
list forces the user to scroll way down to see the README.md. This
PR fixes that by storing the documents in separate sub-folders one
per hierarchy of related documents. Also changed
Documentation\README.md and root README.md to take into account
the new paths.
Commit migrated from 8d3936bff7
