Program Optimization Lab 2018

Aim of the Program Optimization Lab 2018 is to explore the LLVM opt tool and extend it with an advanced Value-Set Analysis according to Reps et al..

A PDF version of the presentation we gave at the end of the course is available here.

Authors (in alphabetic order)

• Julian Erhard
• Jakob Gottfriedsen
• Peter Munch
• Alexander Roschlaub
• Michael B. Schwarz

Installation

Clone the project into the following folder:

cd llvm/lib/Transforms
git clone [email protected]:peterrum/po-lab-2018.git
mv po-lab-2018 ValueSetAnalysis

and add the following line to the CMakeLists.txt-file:

add_subdirectory(ValueSetAnalysis)
add_subdirectory(ValueSetAnalysis/tutorial)
add_subdirectory(ValueSetAnalysis/benchmark)

Finally run make and/or make install again.

How to ...

... view IR

Recompile and view output with your favorite text editor:

clang -Os -S -emit-llvm hello.c -o hello.ll

In the case you have already a .bc-file run the following to get the .ll-file:

llvm-dis hello-opt.bc

... use opt

clang -Os -S -emit-llvm hello.c -o hello.ll

clang -O3 -emit-llvm hello.c -c -o hello.bc
opt -load llvm/lib/llvm-vsa.so -vsapass < hello.bc > /dev/null

... useful workflow

clang -O0 -emit-llvm hello.c -Xclang -disable-O0-optnone -c -o hello.bc
opt -mem2reg < hello.bc > hello-opt.bc
opt -load llvm/lib/llvm-vsa.so -vsapass < hello.bc > /dev/null

Useful classes and methods in LLVM

• Write output: errs() << "Hello World!\n"

llvm::Module

• Iterator over all functions

llvm::Function

• Iterator over all basic blocks
• getName()

llvm::BasicBlock

• Iterator over all instructions

llvm::Instruction

• getOpcodeName()
• getValueID()
• users()

llvm::InstVisitor<U, V>

• V visit(...)

llvm::APInt

• Arbitrary precision integer