While compiling some code I noticed big differences in the assembler created between -O0 and -O1. I wanted to run through enabling/disabling optimisations until I found out what was causing a certain change in the assembler.
If I use -fverbose-asm to find out exactly which flags O1 is enabling compared to O0, and then disable them manually, why is the assembler produced still so massively different? Even if I run gcc with O0 and manually add all the flags that fverbose-asm said were enabled with O1, I don't get the same assembler that I would have got just by using O1.
Is there anything apart from '-f...' and '-m...' that can be changed?
Or is is just that 'O1' has some magic compared with 'O0' that cannot be turned off.
Sorry for the crypticness - this was related to Reducing stack usage during recursion with GCC + ARM however the mention of it was making the question a bit hard to understand.