Optimize castToDeclContext for 2% improvement in build times
castToDeclContext is a heavily used function, and as such, it needs to
be kept as slim as feasible to preserve as much performance as possible.
To this end, it was observed that the function was generating suboptimal
assembly code, and putting the most common execution path in the longest
sequence of instructions. This patch addresses this by guiding the
compiler towards generating a lookup table of offsets, which can be used
to perform an addition on the pointer. This results in a 1-2%
improvement on debug builds (and a negligible improvement on release).
To achieve this, the switch was simplified to flatten the if statements
in the default branch. In order to make the values of the switch more
compact, encouraging LLVM to generate a look-up table instead of a jump
table, the AST TableGen generator was modified so it can take order
priority based on class inheritance. This combination allowed for a more
optimal generation of the function. Of note, 2 other functions with an
equivalent structure also needed to be modified.
Fixes#76824
This is how it should've been and brings it more in line with
std::string_view. There should be no functional change here.
This is mostly mechanical from a custom clang-tidy check, with a lot of
manual fixups. It uncovers a lot of minor inefficiencies.
This doesn't actually modify StringRef yet, I'll do that in a follow-up.
the tblgen AST node hierarchies.
Not totally NFC because both of the emitters now emit in a different
order. The type-nodes emitter now visits nodes in hierarchy order,
which means we could use range checks in classof if we had any types
that would benefit from that; currently we do not. The AST-nodes
emitter now uses a multimap keyed by the name of the record; previously
it was using `Record*`, which of couse isn't stable across processes
and may have led to non-reproducible builds in some circumstances.
to reflect the new license.
We understand that people may be surprised that we're moving the header
entirely to discuss the new license. We checked this carefully with the
Foundation's lawyer and we believe this is the correct approach.
Essentially, all code in the project is now made available by the LLVM
project under our new license, so you will see that the license headers
include that license only. Some of our contributors have contributed
code under our old license, and accordingly, we have retained a copy of
our old license notice in the top-level files in each project and
repository.
llvm-svn: 351636
