How to use

Go through the commit to learn LLVM IR.

LLVM IR syntax basic

Using LLVM IR C++ API to generate LLVM IR.

Covered:

• Create module
• Create function
• Create Basic Block
• Emit global variable
• Declare If-else function
• Declare Loop
• Pointer manipulation
• Vector manipulation

Environment

$ lli --version
LLVM (http://llvm.org/):
  LLVM version 10.0.1
  Optimized build.
  Default target: x86_64-apple-darwin18.2.0
  Host CPU: broadwell
$ clang++ --version
clang version 10.0.1
Target: x86_64-apple-darwin18.2.0
Thread model: posix
InstalledDir: /usr/local/opt/llvm/bin

Compile and run (remove libxml2 from compile option if not found):

$ clang++ module.cpp `llvm-config --cxxflags --ldflags --system-libs --libs core` -fno-rtti -o module
$ ./module

Tips

• ICmp instruciton output variable of type Int1
• getelementptr calculates address, doesn't access data
• Vector types are used when multiple primitive data are operated in parallel
• Phi Node is used to implement the φ node in the SSA graph representing the function. It is an instruction used to select a value depending on the predecessor of the current block. Phi nodes are necessary due to the structure of the SSA (static single assignment) style of the LLVM code.