iPhone compile for thumb

Question

I\'ve heard it might be a good idea to turn off \"compile for thumb\" in an iPhone target\'s settings to increase performance. I\'m having some trouble finding this setting thou

Answer 1

The standard instruction set for ARM is 4-bytes. Using "Compile for Thumb", the compiler is able to use 2-byte instructions. This results in a much smaller library, but also a slower one (somewhat debatable). More critically, there are issues with running under ARMv6. In our case, we could not generate stable output from Monotouch (fix in MT4.0 alpha). In Xcode, you can find the setting by clicking on your Target, and looking under Build and searching for "thumb". Mine is under GCC 4.2 - Code Generation, but sometimes it is under LVVM GCC 4.2.