LLVM

https://releases.llvm.org/3.6.1/docs/
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LLVM is a collection of modular and reusable compiler and toolchain technologies used for building...
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### YAML sequence example

Source: https://releases.llvm.org/3.6.1/docs/YamlIO.html

Shows the basic YAML sequence syntax where each item starts with a leading dash.

```yaml
# a sequence
- x86
- x86_64
- PowerPC

```

--------------------------------

### Install LLVM/Clang with Ninja

Source: https://releases.llvm.org/3.6.1/docs/HowToCrossCompileLLVM.html

Installs the built LLVM/Clang into the install directory, creating a sysroot.

```shell
$ ninja install

```

--------------------------------

### add instruction example

Source: https://releases.llvm.org/3.6.1/docs/LangRef.html

Example of the 'add' instruction summing two i32 operands.

```llvm
<result> = add i32 4, %var          ; yields i32:result = 4 + %var
```

--------------------------------

### Shell session example

Source: https://releases.llvm.org/3.6.1/docs/SphinxQuickstartTemplate.html

A shell session example showing two commands. Use a `console` code block for shell sessions.

```console
$ echo "Goodbye cruel world!"
$ rm -rf /

```

--------------------------------

### Run opt with -help to list registered passes

Source: https://releases.llvm.org/3.6.1/docs/WritingAnLLVMPass.html

Shows the help output for the opt tool after loading the Hello pass. Use this to verify the pass was registered and to see available options.

```bash
$ opt -load ../../../Debug+Asserts/lib/Hello.so -help
OVERVIEW: llvm .bc -> .bc modular optimizer

USAGE: opt [options] <input bitcode>

```

--------------------------------

### Value::use_begin

Source: https://releases.llvm.org/3.6.1/docs/ProgrammersManual.html

Get an iterator to the start of the use-list.

```APIDOC
## Value::use_begin

### Description
Get an iterator to the start of the use-list.

### Method
use_begin

### Parameters
None

### Returns
- **use_iterator** - Iterator to the start of the use-list.
```

--------------------------------

### User::op_begin

Source: https://releases.llvm.org/3.6.1/docs/ProgrammersManual.html

Get an iterator to the start of the operand list.

```APIDOC
## User::op_begin

### Description
Get an iterator to the start of the operand list.

### Method
op_begin

### Parameters
None

### Returns
- **op_iterator** - Iterator to the start of the operand list.
```

--------------------------------

### Compile and run commands for toy.cpp

Source: https://releases.llvm.org/3.6.1/docs/tutorial/LangImpl4.html

Build the toy example with clang++ using llvm-config flags, then run the resulting binary. On Linux, add the -rdynamic option so external functions resolve properly at runtime.

```bash
# Compile
clang++ -g toy.cpp `llvm-config --cxxflags --ldflags --system-libs --libs core mcjit native` -O3 -o toy
# Run
./toy

```

--------------------------------

### C code block example

Source: https://releases.llvm.org/3.6.1/docs/SphinxQuickstartTemplate.html

A minimal C program that returns 0. Use this as a starting point for code examples in Sphinx documentation.

```c
int main() {
  return 0;
}

```

--------------------------------

### Create hello.c

Source: https://releases.llvm.org/3.6.1/docs/GettingStartedVS.html

Simple C program that prints 'hello world' to standard output. Used as the input for the LLVM tool chain example.

```c
#include <stdio.h>
int main() {
  printf("hello world\n");
  return 0;
}

```

--------------------------------

### Complete toy.cpp LLVM JIT example

Source: https://releases.llvm.org/3.6.1/docs/tutorial/LangImpl4.html

Full C++ source for the toy language frontend with the LLVM JIT and optimizer. Includes the lexer, parser, AST, code generation, and main driver. Build with the clang++ command shown above; on Linux add -rdynamic so external functions resolve at runtime.

```cpp
#include "llvm/Analysis/Passes.h"
#include "llvm/ExecutionEngine/ExecutionEngine.h"
#include "llvm/ExecutionEngine/MCJIT.h"
#include "llvm/ExecutionEngine/SectionMemoryManager.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/DerivedTypes.h"
#include "llvm/IR/IRBuilder.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/Module.h"
#include "llvm/IR/Verifier.h"
#include "llvm/PassManager.h"
#include "llvm/Support/TargetSelect.h"
#include 
```

--------------------------------

### Close anonymous namespace

Source: https://releases.llvm.org/3.6.1/docs/WritingAnLLVMPass.html

Closes the anonymous namespace started earlier in the example.

```cpp
} // end of anonymous namespace
```

--------------------------------

### Example: addr.txt input file

Source: https://releases.llvm.org/3.6.1/docs/CommandGuide/llvm-symbolizer.html

Input file listing object file paths and addresses, one per line, that llvm-symbolizer reads from standard input.

```text
$ cat addr.txt
a.out 0x4004f4
/tmp/b.out 0x400528
/tmp/c.so 0x710
/tmp/mach_universal_binary:i386 0x1f84
/tmp/mach_universal_binary:x86_64 0x100000f24

```

--------------------------------

### Kaleidoscope 'for' loop example with putchard

Source: https://releases.llvm.org/3.6.1/docs/tutorial/LangImpl5.html

Defines a 'for' loop expression in Kaleidoscope that iterates a variable from a starting value while a condition holds. The example prints 100 '*' characters by calling putchard(42) inside the loop body.

```kaleidoscope
extern putchard(char)
def printstar(n)
  for i = 1, i < n, 1.0 in
    putchard(42);  # ascii 42 = '*'

# print 100 '*' characters
printstar(100);
```

--------------------------------

### Compile sample.ll with llc -load=MyGC.so

Source: https://releases.llvm.org/3.6.1/docs/GarbageCollection.html

Compile a sample LLVM IR file that uses the "mygc" GC attribute, then run it through llvm-as and llc with the plugin loaded via -load=MyGC.so. The plugin may have a platform-specific extension.

```shell
$ cat sample.ll
define void @f() gc "mygc" {
entry:
  ret void
}
$ llvm-as < sample.ll | llc -load=MyGC.so

```

--------------------------------

### Basic Shape class hierarchy for LLVM-style RTTI

Source: https://releases.llvm.org/3.6.1/docs/HowToSetUpLLVMStyleRTTI.html

Defines the Shape class used as the base for setting up LLVM-style RTTI. This is the starting point for the basic setup described in the section.

```cpp
class Shape {
public:
  Shape() {}
}
```

--------------------------------

### Build gold with plugin support

Source: https://releases.llvm.org/3.6.1/docs/GoldPlugin.html

Download, configure, and build gold with plugin support. Requires git, make, and a C toolchain. The resulting build/gold/ld-new supports the -plugin option, and running make additionally builds build/binutils/ar and nm.

```shell
$ git clone --depth 1 git://sourceware.org/git/binutils-gdb.git binutils
$ mkdir build
$ cd build
$ ../binutils/configure --enable-gold --enable-plugins --disable-werror
$ make all-gold

```

--------------------------------

### Set up git-svn clone for LLVM

Source: https://releases.llvm.org/3.6.1/docs/GettingStarted.html

Commands to clone the LLVM repository and initialize git-svn for submitting code. Includes optional setup for clang. Requires a valid SVN username.

```shell
% git clone http://llvm.org/git/llvm.git
% cd llvm
% git svn init https://llvm.org/svn/llvm-project/llvm/trunk --username=<username>
% git config svn-remote.svn.fetch :refs/remotes/origin/master
% git svn rebase -l  # -l avoids fetching ahead of the git mirror.

# If you have clang too:
% cd tools
% git clone http://llvm.org/git/clang.git
% cd clang
% git svn init https://llvm.org/svn/llvm-project/cfe/trunk --username=<username>
% git config svn-remote.svn.fetch :refs/remotes/origin/master
% git svn rebase -l

```

--------------------------------

### Build and run commands for toy.cpp

Source: https://releases.llvm.org/3.6.1/docs/tutorial/LangImpl5.html

Compile the toy.cpp file with clang++ and LLVM flags, then run the resulting executable. Use these commands to build and test the Kaleidoscope example.

```bash
# Compile
clang++ -g toy.cpp `llvm-config --cxxflags --ldflags --system-libs --libs core mcjit native` -O3 -o toy
# Run
./toy
```

--------------------------------

### sub instruction example

Source: https://releases.llvm.org/3.6.1/docs/LangRef.html

Examples of the 'sub' instruction computing differences and negation.

```llvm
<result> = sub i32 4, %var          ; yields i32:result = 4 - %var
<result> = sub i32 0, %val          ; yields i32:result = -%var
```

--------------------------------

### fadd instruction example

Source: https://releases.llvm.org/3.6.1/docs/LangRef.html

Example of the 'fadd' instruction summing two float operands.

```llvm
<result> = fadd float 4.0, %var          ; yields float:result = 4.0 + %var
```

--------------------------------

### Check out Test Suite Source Code (optional)

Source: https://releases.llvm.org/3.6.1/docs/GettingStarted.html

Clones the test-suite repository into the llvm/projects directory. This step is optional.

```bash
% cd llvm/projects
% git clone http://llvm.org/git/test-suite.git

```

--------------------------------

### Example statistics output from opt -stats

Source: https://releases.llvm.org/3.6.1/docs/ProgrammersManual.html

Example report from running opt on a C file from the SPEC benchmark suite, showing the unified format of statistics from various passes.

```text
  7646 bitcodewriter   - Number of normal instructions
   725 bitcodewriter   - Number of oversized instructions
129996 bitcodewriter   - Number of bitcode bytes written
  2817 raise           - Number of insts DCEd or constprop'd
  3213 raise           - Number of cast-of-self removed
  5046 raise           - Number of expression trees converted
    75 raise           - Number of other getelementptr's formed
   138 raise           - Number of load/store peepholes
    42 deadtypeelim    - Number of unused typenames removed from symtab
   392 funcresolve     - Number of varargs functions resolved
    27 globaldce       - Number of global variables removed
     2 adce            - Number of basic blocks removed
   134 cee             - Number of branches revectored
    49 cee             - Number of setcc instruction eliminated
   532 gcse            - Number of loads removed
  2919 gcse            - Number of instructions removed
    86 indvars         - Number of canonical indvars added
    87 indvars         - Number of aux indvars removed
    25 instcombine     - Number of dead inst eliminate
   434 instcombine     - Number of insts combined
   248 licm            - Number of load insts hoisted
  1298 licm            - Number of insts hoisted to a loop pre-header
     3 licm            - Number of insts hoisted to multiple loop preds (bad, no loop pre-header)
    75 mem2reg         - Number of alloca's promoted
  1444 cfgsimplify     - Number of blocks simplified
```

--------------------------------

### resume instruction example

Source: https://releases.llvm.org/3.6.1/docs/LangRef.html

Example of the 'resume' instruction resuming exception propagation with a landingpad value.

```llvm
resume { i8*, i32 } %exn
```

--------------------------------

### Additional assert examples

Source: https://releases.llvm.org/3.6.1/docs/CodingStandards.html

More examples of assert statements with descriptive error messages for various conditions.

```cpp
assert(Ty->isPointerType() && "Can't allocate a non-pointer type!");

assert((Opcode == Shl || Opcode == Shr) && "ShiftInst Opcode invalid!");

assert(idx < getNumSuccessors() && "Successor # out of range!");

assert(V1.getType() == V2.getType() && "Constant types must be identical!");

assert(isa<PHINode>(Succ->front()) && "Only works on PHId BBs!");

```

--------------------------------

### sext instruction examples

Source: https://releases.llvm.org/3.6.1/docs/LangRef.html

Examples of sign-extending integers and vectors, including from i1 where result is -1 or 0.

```llvm
%X = sext i8  -1 to i16              ; yields i16   :65535
%Y = sext i1 true to i32             ; yields i32:-1
%Z = sext <2 x i16> <i16 8, i16 7> to <2 x i32> ; yields <i32 8, i32 7>
```

--------------------------------

### Compile and run toy.cpp

Source: https://releases.llvm.org/3.6.1/docs/tutorial/LangImpl2.html

Compile the toy.cpp file with clang++ using -g and -O3 flags, then run the resulting executable a.out.

```bash
# Compile
clang++ -g -O3 toy.cpp
# Run
./a.out

```

--------------------------------

### zext instruction examples

Source: https://releases.llvm.org/3.6.1/docs/LangRef.html

Examples of zero-extending integers and vectors, including from i1 where result is 0 or 1.

```llvm
%X = zext i32 257 to i64              ; yields i64:257
%Y = zext i1 true to i32              ; yields i32:1
%Z = zext <2 x i16> <i16 8, i16 7> to <2 x i32> ; yields <i32 8, i32 7>
```
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