[RISCV] Split SP adjustment to reduce the offset of callee saved register spill and restore
We would like to split the SP adjustment to reduce the instructions in
prologue and epilogue as the following case. In this way, the offset of
the callee saved register could fit in a single store.
add sp,sp,-2032 sw ra,2028(sp) sw s0,2024(sp) sw s1,2020(sp) sw s3,2012(sp) sw s4,2008(sp) add sp,sp,-64
Differential Revision: https://reviews.llvm.org/D68011