This is a first attempt at a constant value consecutive store merging pass,
a counterpart to the DAGCombiner's store merging optimization.
The high level goals of this pass:
* Have a simple and efficient algorithm. As close to linear time as we can get.
Thus, prioritizing scalability of the algorithm over merging every corner case
we can find. The DAGCombiner's store merging code has been the source of
compile time and complexity issues in the past and I wanted to avoid that.
* Don't introduce any new data structures for ordering memory operations. In MIR,
we don't have the concept of chains like we do in the DAG, and the instruction
order is stricter than enforcing ordering with graph edges. Although I
considered adding something similar, I couldn't justify the overhead.
The pass is current split into 3 main parts. The main store merging code focuses
on identifying candidate stores and managing the candidate group that's under
consideration for merging. Analyzing addressing of stores is a potentially
complex part and for now there's just a basic implementation to identify easy
cases. Finally, the other main bit of complexity is the alias analysis, which
tries to follow the same logic as the DAG's AA.
Currently this implementation only supports merging of constant stores. Stores
of arbitrary variables are technically possible with a very small change, but
the DAG chooses not to do this. Doing so here makes most code worse since
there's extra overhead in merging values into wider registers.
On AArch64 -Os, this optimization results in very minor savings on CTMark.
Differential Revision: https://reviews.llvm.org/D109131
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
With this change, the GlobalISel library gets always built. In
particular, this is not possible to opt GlobalISel out of the build
using the LLVM_BUILD_GLOBAL_ISEL variable any more.
llvm-svn: 309990
This reverts commit r299287 plus clean-ups.
The localizer pass is a helper pass that could be run at O0 in the GISel
pipeline to work around the deficiency of the fast register allocator.
It basically shortens the live-ranges of the constants so that the
allocator does not spill all over the place.
Long term fix would be to make the greedy allocator fast.
llvm-svn: 304051
The previous names were both misleading (the MachineLegalizer actually
contained the info tables) and inconsistent with the selector & translator (in
having a "Machine") prefix. This should make everything sensible again.
The only functional change is the name of a couple of command-line options.
llvm-svn: 284287
This adds the actual MachineLegalizeHelper to do the work and a trivial pass
wrapper that legalizes all instructions in a MachineFunction. Currently the
only transformation supported is splitting up a vector G_ADD into one acting on
smaller vectors.
llvm-svn: 276461
