On Mon, 2006-06-26 at 17:48, Shaun Jackman wrote: > The default -mpic-register (on ARM/Thumb) is r10. In -mthumb mode, r10 > is not available to the math instructions as a direct argument. On top > of that, preserving r10 complicates the function prologue. Does it > make more sense to use a directly accessible register, r7 for example, > as the default -mpic-register when in -mthumb mode? Can a > non-preserved register, such as r3, be used instead? (assuming the > compiler saves the function argument in r3 somewhere) > > Why is the PIC register fixed? Could the compiler register allocation > logic be allowed to allocate the _GLOBAL_OFFSET_TABLE_ pointer the > same as any other variable? In which case it would probably realise > that > cost(r3) < cost(r7) < cost(r10) > at least in the case where r3 isn't being used by a function argument.
As of gcc-4.2 it isn't fixed, it's just like any other pseudo generated by the compiler. R.
