Using AArch64's original implementation for reference, this patch
implements a pass to remove unneeded copies of X0. This pass runs
after register allocation and looks to see if a register is implied
to be 0 by a branch in the predecessor basic block.
Reviewed By: asb
Differential Revision: https://reviews.llvm.org/D118160
Similar for ceil, trunc, round, and roundeven. This allows us to use
static rounding modes to avoid a libcall.
This is similar to D116771, but for the saturating conversions.
This optimization is done for AArch64 as isel patterns.
RISCV doesn't have instructions for ceil/floor/trunc/round/roundeven
so the operations don't stick around until isel to enable a pattern
match. Thus I've implemented a DAG combine.
I'm only handling saturating to i64 or i32. This could be extended
to other sizes in the future.
Reviewed By: asb
Differential Revision: https://reviews.llvm.org/D116864
Shao-Ce SUN