Example: Compiling using existing language frontend

Let's try to use a simple C file to test our compiler:

cat <<EOF > test.c
unsigned x;
int abc(unsigned a, unsigned b, unsigned c) {
  if (c > 0) {
    return a + x;
  } else {
    return a + b;
  }
}
EOF

Prerequisite: You have to install clang and use it to generate LLVM IR first:

clang -S -emit-llvm test.c

This will generate a test.ll file which should be the LLVM IR equivalent of our test.c file. Then we can generate EVM binary or assembly from it. In order to use the backend to generate EVM assembly, you have to specify -mtriple=evm when calling llc. An example is as follows:

./build/bin/llc -mtriple=evm test.ll -o test.s

The generated test.s file contains the compiled EVM assembly code. Note that the generated code is the function body itself. In order to generate a complete smart contract source code we need to use a smart contract creator function, which we will talk about it in another page.

Notice that you can also get the binary code of the function body by emitting an object file:

./build/bin/llc -mtriple=evm -filetype=obj test.ll -o test.o