LLVMCookBook

This project will work throughout the example inside "LLVM CookBook", which write a frontend for a TOY language and then the optimizer, backend. Newer versions of LLVM are released since the book published, the difference will be explained as "Version Updates Notes". While the errata will also be explained as "Book Errata"

Environments:

• MacOS Mojave version 10.14.4
• LLVM 7.0.0
• clang 7.0.0

Chapter-1

Introduces some common-used llvm tools

Chapter-2

Introduces a front-end for a TOY language. example:

def foo(x y)
x + y * 16;

Use the following command to generate IR for example:

$make
$./toy example

LLVM IR:

; ModuleID = 'example'
source_filename = "example"

define i32 @foo(i32 %x, i32 %y) {
entry:
  %multmp = mul i32 %y, 16
  %addtmp = add i32 %x, %multmp
  ret i32 %addtmp
}

Book Errata: According to the implementation of lexer, the arguments in example should be separated by space instead of comma. Version Updates Notes: Some variables in lexer and parser are changed to be pointer type instead of primitive type, please refer to the code for details.

Chapter-3

Add the if/for/binary/unary statement or operations for front-end, and also add the JIT support, go to the corresponding directory:

$make
$./toy example

if-else

example:

def fib(x)
if x < 3 then
1
else
fib(x-1)+fib(x-2)

LLVM IR:

; ModuleID = 'example'
source_filename = "example"

define i32 @fib(i32 %x) {
entry:
  %cmptmp = icmp ult i32 %x, 3
  %booltmp = zext i1 %cmptmp to i32
  %ifcond = icmp ne i32 %booltmp, 0
  br i1 %ifcond, label %then, label %else

then:                                             ; preds = %entry
  br label %ifcont

else:                                             ; preds = %entry
  %subtmp = sub i32 %x, 1
  %calltemp = call i32 @fib(i32 %subtmp)
  %subtmp1 = sub i32 %x, 2
  %calltemp2 = call i32 @fib(i32 %subtmp1)
  %addtmp = add i32 %calltemp, %calltemp2
  br label %ifcont

ifcont:                                           ; preds = %else, %then
  %iftmp = phi i32 [ 1, %then ], [ %addtmp, %else ]
  ret i32 %iftmp
}

loop

example:

def printstar(n x)
    for i = 1, i < n, 1 in
        x + 1

LLVM IR:

; ModuleID = 'example'
source_filename = "example"

define i32 @printstar(i32 %n, i32 %x) {
entry:
  br label %loop

loop:                                             ; preds = %loop, %entry
  %i = phi i32 [ 1, %entry ], [ %nextvar, %loop ]
  %addtmp = add i32 %x, 1
  %nextvar = add i32 %i, 1
  %cmptmp = icmp ult i32 %i, %n
  %booltmp = zext i1 %cmptmp to i32
  %loopcond = icmp ne i32 %booltmp, 0
  br i1 %loopcond, label %loop, label %afterloop

afterloop:                                        ; preds = %loop
  ret i32 0
}

binary

example:

def binary| 5 (LHS RHS)
    if LHS then
        1
    else if RHS then
        1
    else
        0;

LLVM IR:

source_filename = "example"

define i32 @"binary|"(i32 %LHS, i32 %RHS) {
entry:
  %ifcond = icmp ne i32 %LHS, 0
  br i1 %ifcond, label %then, label %else

then:                                             ; preds = %entry
  br label %ifcont4

else:                                             ; preds = %entry
  %ifcond1 = icmp ne i32 %RHS, 0
  br i1 %ifcond1, label %then2, label %else3

then2:                                            ; preds = %else
  br label %ifcont

else3:                                            ; preds = %else
  br label %ifcont

ifcont:                                           ; preds = %else3, %then2
  %iftmp = phi i32 [ 1, %then2 ], [ 0, %else3 ]
  br label %ifcont4

ifcont4:                                          ; preds = %ifcont, %then
  %iftmp5 = phi i32 [ 1, %then ], [ %iftmp, %ifcont ]
  ret i32 %iftmp5
}

unary

example:

def unary!(v)
    if v then
        0
    else
        1;

LLVM IR:

define i32 @"unary!"(i32 %v) {
entry:
  %ifcond = icmp ne i32 %v, 0
  br i1 %ifcond, label %then, label %else

then:                                             ; preds = %entry
  br label %ifcont

else:                                             ; preds = %entry
  br label %ifcont

ifcont:                                           ; preds = %else, %then
  %iftmp = phi i32 [ 0, %then ], [ 1, %else ]
  ret i32 %iftmp
}

JIT Support

example:

def f()
    4+5;

LLVM IR:

; ModuleID = 'example'
source_filename = "example"

define i32 @f() {
entry:
  ret i32 9
}

Chapter-4

This chapter introduces writing the LLVM pass, there are a few tasks. ###1. Writing your own pass Put FuncBolckCount under /dir/to/llvm/src/lib/Transforms Then add the following line to CMakeLists.txt under /dir/to/llvm/src/lib/Transforms:

add_subdirectory(FuncBlockCount)

Then go to /dir/to/llvm/src/../ and create a build folder

$cd build
$cmake -G "Unix Makefiles" ../llvm-7.0.0.src
$make
$opt -load dir/to/build/lib/funcBlockCountlib.dylib -funcblockcount sample.ll

Output:

Function foo
Function ha

###2. Using another pass in a new pass Put FuncBolckCount under /dir/to/llvm/src/lib/Transforms, go to the build folder created in the first task

$make
$opt -load ../../../llvm/build/lib/funcBlockCountlib.dylib -funcblockcount sample.ll

Output:

Function main
Loop level 0 has 11 blocks
Loop level 1 has 3 blocks
Loop level 1 has 3 blocks
Loop level 0 has 15 blocks
Loop level 1 has 7 blocks
Loop level 2 has 3 blocks
Loop level 1 has 3 blocks

###3. Registering a pass with pass manager

opt -funcblockcount example.ll

Output:

Function main
Loop level 0 has 11 blocks
Loop level 1 has 3 blocks
Loop level 1 has 3 blocks
Loop level 0 has 15 blocks
Loop level 1 has 7 blocks
Loop level 2 has 3 blocks
Loop level 1 has 3 blocks

Version Updates Notes:Include "llvm/Transforms/Scalar.h" in FuncBlockCount.cpp ###4. Write an analysis pass This task implement a function pass, and the work scheme is the same as task 1.

$opt -load dir/to/build/lib/LLVMCountopcodes.dylib -opcodeCounter -disable-output testcode.bc

Output:

Function func
add: 3
alloca: 5
br: 8
icmp: 3
load: 10
ret: 1
select: 1
store: 8
zext: 1

###5. Write an alias analysis pass Have no idea if the method in book still works ###6. Using other analysis passes This task shows some build-in passes, there's no difficulty to do so now.