llvm patched with systemc library

By Rui Chen

In this article, I will get into the IR generated by the llvm-g++ along with the systemc library.

Understand the installation flow of PinaVM
The project is to mimic the idea of PinaVM, but I have to repeat the first few steps to understand the relationship between llvm-g++ and systemc library. Check out the /doc/install document for details.

One limit is that you have to use LLVM 2.6, which may suffer incompatible features with the latest version.

Start from autoconf part, which is Step 3 in the manual
1. autoconf
What the autoconf do is to seek a file named configure.ac (or configure.in for backward compatibility), and then runs the M4 macro processor to create the configure script.

2. configrue
command ./configure --with-tools-dir=$DOWNLOAD
Part of the output:

configure: Summary of variables:

DOWNLOAD_AND_COMPILE_DIR: /home/chenrui/Desktop/pinavm/download
INSTALL_PATH_LLVM: /home/chenrui/Desktop/pinavm/lib/llvm-2.7
INSTALL_PATH_LLVMGCC: /home/chenrui/Desktop/pinavm/lib/llvm-gcc
INSTALL_PATH_SYSTEMC_LLVM: /home/chenrui/Desktop/pinavm/lib/systemc-2.2.0-llvm
INSTALL_PATH_SYSTEMC_GCC: /home/chenrui/Desktop/pinavm/lib/systemc-2.2.0-gcc

configure: creating ./config.status
config.status: creating config.mk
config.status: creating config.sh

The code in the configure.ac file:

DOWNLOAD_AND_COMPILE_DIR="${TOOLS_DIR}/download"
INSTALL_PATH_LLVM=${TOOLS_DIR}/lib/llvm-2.7
INSTALL_PATH_LLVMGCC=${TOOLS_DIR}/lib/llvm-gcc
INSTALL_PATH_SYSTEMC_LLVM=${TOOLS_DIR}/lib/systemc-2.2.0-llvm
INSTALL_PATH_SYSTEMC_GCC=${TOOLS_DIR}/lib/systemc-2.2.0-gcc

So the "--with-tools-dir" means specifying the $DOWNLOAD directory for ${TOOLS_DIR}.

Another part of configure.ac:

# Defining files to be generated
AC_CONFIG_FILES([config.mk
                 config.sh])

Then config.mk and config.sh will be generated.
NOTE: normally, AC_CONFIG_FILES([Makefile]) is used(ref link).

Motivation to use SystemC and LLVM
I have done a simple literal translator with SystemC-to-VHDL translator with ANTLR, and I think it needs tremendous effort to crack the whole C++ grammar.
Besides, sc2v and gsc and many tools are based on their self-made compilers, which suffers a severe issue that only a small set of systemc grammar can be compiled.

Based on this understanding, it is very important to immigrate the translation method from ANTLR literal way to llvm-g++ based.


Generate simple backend first.
Another idea about working with C++ & Systemc with LLVM is that I can generate a VHDL experiment backend for test first and then connect it to the systemc frontend.