[LLVMdev] GSoC 2009: An LLVM Backend for TPA

lu lu lulu760 at gmail.com
Wed Apr 1 21:53:04 PDT 2009

Hi all,
I'd like to write an LLVM backend for TPA processor architecture as part of
2009's Google Summer of Code program.

TPA processor is a new architecture that offers the possibility of high
instruction-level parallelism with energy efficiency. TPA architecture
partitions the work between the compiler and the hardware differently from
RISC and CISC architectures. TPA architecture has three different features
that require new complier support. First, the compiler is responsible for
partitioning the program into a sequence of structured blocks, which
logically execute atomically. Secondly, the compiler should encode
instruction dependences explicitly, eliminating the need for the hardware to
discover dependences dynamically. The instructions within each block
communicate directly, instead of communicating through shared registers. The
TPA architecture could impose restrictions on its blocks to simplify the
microarchitecture. Third, the compiler should statically schedule the
instruction for the dynamic issuing model.

Based on the required of the TPA architecture, the project has three main
tasks: Fisrt, writing an LLVM backend could produce TPA machine code.
Secondly, we’ll optimize the method of producing the TPA blocks so that the
blocks are full of useful instructions while enforcing the architecture
constraints. Third, we’ll optimize the instruction scheduler so that
instructions in the block can execute with minimum cost.

Besides the basic LLVM backend for TPA processor, two passes are crucial for
our research work. One is function pass called Hyperblock_Formation, which
partition several basic blocks into a TPA block. We'll use a collection of
heuristics, such as critical path ordering, load balancing, data cache
locality, register output and so on. The other is a block pass called
instruction block, which statically maps the instructions to the processor.
To implement the instruction scheduler, we'll use another set of heuristics,
such as placement for locality, contention, effective window size, etc.

As for my personal background, I'm a graduate student at University of
Science and Technology of China with a strong background in compiler theory.
My major is computer architecture, the mainly job of my team is to research
a new architecture that could take full advantage of hardware resource to
speed up the programs. Recently, we have proposed data-like driven TPA
architecture, so we should implement a compiler for it. I choose LLVM as an
auxiliary framework. I believe this project will be useful to our research
and we'll give a TPA target backend to the LLVM community.
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