Using DragonEgg

Dragonegg is a gcc plugin that allows gcc to make use of the LLVM optimizer and code generator instead of gcc's own optimizer and code generator.

Getting ready

You need to have gcc 4.5 or above, with the target machine being x86-32/x86-64 and an ARM processor. Also, you need to download the dragonegg source code and build the dragonegg.so file.

How to do It…

Do the following steps:

1. Create a simple hello world program:

   $ cat testprog.c
   #include<stdio.h>
   int main() {
   printf("hello world");
   }
   

2. Compile this program with your gcc; here we use gcc-4.5:

   $ gcc testprog.c -S -O1 -o -
     .file  " testprog.c"
     .section  .rodata.str1.1,"aMS",@progbits,1
   .LC0:
     .string  "Hello world!"
     .text
   .globl main
     .type  main, @function
   main:
     subq  $8, %rsp
     movl  $.LC0, %edi
     call  puts
     movl  $0, %eax
     addq  $8, %rsp
     ret
     .size  main, .-main
   

3. Using the -fplugin=path/dragonegg.so flag in the command line of gcc makes gcc use LLVM's optimizer and LLVM codegen:

   $ gcc testprog.c -S -O1 -o - -fplugin=./dragonegg.so
     .file  " testprog.c"
   # Start of file scope inline assembly
     .ident  "GCC: (GNU) 4.5.0 20090928 (experimental) LLVM: 82450:82981"
   # End of file scope inline assembly
   
   
     .text
     .align  16
     .globl  main
     .type  main,@function
   main:
     subq  $8, %rsp
     movl  $.L.str, %edi
     call  puts
     xorl  %eax, %eax
     addq  $8, %rsp
     ret
     .size  main, .-main
     .type  .L.str,@object
     .section  .rodata.str1.1,"aMS",@progbits,1
   .L.str:
     .asciz  "Hello world!"
     .size  .L.str, 13
   
     .section  .note.GNU-stack,"",@progbits
   

See also

• To know about how to get the source code and installation procedure, refer to http://dragonegg.llvm.org/