llvm

Table of Contents Overview Websites LLVM Coroutines Basic Concepts Tools llvm-as: Assembler llvm-dis: Disassembler LLVM Compiler Compiler Runtime Clang

Overview

Websites

• Webpage: http://llvm.org
• AOSA book chapter: http://www.aosabook.org/en/llvm.html
• LLVM Documentation: http://llvm.org/docs/
  • LLVM Tutorial (Kaleidoscope): http://llvm.org/docs/tutorial/index.html
  • LLVM Passes: http://llvm.org/docs/Passes.html

LLVM Coroutines

• https://llvm.org/docs/Coroutines.html

Basic Concepts

• LLVM IR: .ll file

define i32 @add1(i32 %a, i32 %b) {
entry:
  %tmp1 = add i32 %a, %b
  ret i32 %tmp1
}

define i32 @add2(i32 %a, i32 %b) {
entry:
  %tmp1 = icmp eq i32 %a, 0
  br i1 %tmp1, label %done, label %recurse

recurse:
  %tmp2 = sub i32 %a, 1
  %tmp3 = add i32 %b, 1
  %tmp4 = call i32 @add2(i32 %tmp2, i32 %tmp3)
  ret i32 %tmp4

done:
  ret i32 %b
}

Tools

llvm-as: Assembler

• LLVM IR (.ll) => [llvm-as] => BITCODE goop (.bc)

llvm-dis: Disassembler

• LLVM BITCODE (.bc) => [llvm-dis] => LLVM IR (.ll)

LLVM Compiler

Compiler Runtime

Clang

• clang -S -emit-llvm foo.c: Produces foo.ll which is an LLVM IR file.
  • The -emit-llvm option can also be passed to the compiler front-end directly, and not the driver by means of -cc1:
• clang -cc1 foo.c -emit-llvm
  • Produces foo.ll with the IR. -cc1 adds some cool options like -ast-print. Check out -cc1 --help for more details.
• llc foo.ll
  • compiles LLVM IR further to assembly