This patch adds tail call support to the 32-bit Sparc backend.
Two new instructions are defined, TAIL_CALL and TAIL_CALLri. They are
encoded the same as CALL and BINDri, but are marked with isReturn so
that the epilogue gets emitted. In contrast to CALL, TAIL_CALL is not
marked with isCall. This makes it possible to use the leaf function
optimization when the only call a function makes is a tail call.
TAIL_CALL modifies the return address in %o7, so for leaf functions
the value in %o7 needs to be restored after the call. For normal
functions which uses the restore instruction this is not necessary.
Reviewed By: koakuma
Differential Revision: https://reviews.llvm.org/D51206
Daniel Cederman