11.3 Optimization switches

This is where the various optimizing switches and their actions are described, grouped per switch.

with n = 1..3: these switches activate the optimizer. A higher level automatically includes all lower levels.
This causes the code generator (and optimizer, IF activated), to favor faster, but code-wise larger, instruction sequences (such as ”subl $4,%esp”) instead of slower, smaller instructions (”enter $4”). This is the default setting.
This one is exactly the reverse of -OG, and as such these switches are mutually exclusive: enabling one will disable the other.
This setting causes the code generator to check which variables are used most, so it can keep those in a register.
with n = 1..3: Setting the target processor does NOT activate the optimizer. It merely influences the code generator and, if activated, the optimizer:
This enables uncertain optimizations. You cannot use these always, however. The previous section explains when they can be used, and when they cannot be used.