What extra optimisation does g++ do with -Ofast?

c++, compiler-construction, gcc, optimization, performance

Solution

Here's a command for checking what options are enabled with -Ofast:

$ g++ -c -Q -Ofast --help=optimizers | grep enabled

Since I only have g++ 4.4 that doesn't support -Ofast, I can't show you the output.

Problem

In g++ 4.6 (or later), what extra optimisations does -Ofast enable other than -ffast-math? The man page says this option "also enables optimizations that are not valid for all standard compliant programs". Where can I find more information about whether this might affect my program or not?

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