On Sat, 3 Feb 2001, Kerstin Hoef-Emden wrote: > when I received my Alpha, I was told to use the compiler-option > -Wa,-m21164a. Reading a little bit in the gcc info, I didn�t find this > option (since gcc never complains, when I use it, it seems to exist), > but I found -mcpu=CPU-type. What is the difference between the two > options? Is one more recommendable than the other?
I would use -mcpu= before -Wa,-m21164a in general, but that really depends on what you're looking to do. The -Wa option passes the -m21164a option to the assembler, which can help schedule the code better for a particular CPU variant, but -mcpu= can actually allow gcc to generate/omit instructions depending on the CPU variant (as well as tell the assembler to schedule the code better). Basically, any -Wa, option just passes whatever follows the comma to the assembler without the compiler looking at it, but -mcpu= lets the compiler target it's output towards that CPU type. > One thing I was told to use as well, was -mieee. What are the comments > on this item? Does it slow down the execution of the code? The -mieee option is a special case, IMO. If you have code that needs it (ie, anything that needs IEEE math compliance or anything that will generate a SIGFPE), use it. If not, it does slow down the code and bloats it a bit. There have been frequent discussions about compiling the entire Alpha deb tree with -mieee, but so far, nobody has made a convincing enough argument for it to justify the general slow-down that we would see. In reality, though, for small binaries like 'ls', it won't make a noticable difference, but larger software would make it very apparent. C
