This is the rest of the solution for PR43520. The IA-64 port has some
register classes in which all of the registers are fixed. The
scheduling reg pressure code in ira sees that we have a class with 0
allocatable registers and decides to add extra dependencies to prevent
increasing register pressure. But if we have no allocatable registers,
then we can't possibly have a register pressure problem. So ira should
be ignoring classes with no allocatable registers.
This patch was tested with an ia64-linux C and C++ bootstrap and make
check. I also verified by hand that is solves the original problem.
I also tested this with an x86-linux bootstrap (all default languages)
and make check. There were no regressions. I did this with an extra
line added
ira_assert (ira_available_class_regs[cl] != 0);
The assert never triggered showing that this patch has no effect on
32-bit x86-linux code.
OK?