[LLVMdev] LTO, plugins and binary sizes

[Rafael Espindola]

For some time now I was curious on what the size impact of LTO was. I
decided to test this with a large C++ app, clang was a natural choice.
With PR8313 fixed with the proposed patch and PR8300 avoided by
disabling constructor aliasing I was able to hack clang to bootstrap
with LTO enabled using the gold plugin.

I did the testing on linux x86-64. Gcc is the 4.4.4 included with
Fedora 13. The results are:

gcc -O3: 32MB
gcc -Os: 25MB
clang lto -Os:  22MB

I then decided to try to link without export-dynamic, since it
produces some fairly large tables and blocks many optimizations. The
new results were

gcc -O3: 30MB
gcc -Os: 23MB
clang lto -Os: 18 MB

The full patches I used are attached. I hope to get the non-hackish
bits reviewed, starting by the fix to 8313.

Cheers,
-- 
Rafael Ávila de Espíndola