This patch constructs codegen infra and successfully generate the first
'add' instruction. Add integer calling convention for fixed arguments which
are passed with general-purpose registers.
New test added here:
CodeGen/LoongArch/ir-instruction/add.ll
The test file is placed in a subdirectory because we will use
subdirctories to distinguish different categories of tests (e.g.
intrinsic, inline-asm ...)
Reviewed By: MaskRay, SixWeining
Differential Revision: https://reviews.llvm.org/D122366
a1c6743922