When SI_PC_ADD_REL_OFFSET is expanded to S_GETPC/S_ADD/S_ADDC, the
GlobalAddress operands have to be adjusted by 4 or 12 bytes to account
for the offset from the end of the S_GETPC instruction to the literal
operands. Do this all in SIInstrInfo::expandPostRAPseudo instead of
duplicating the adjustment code in both AMDGPULegalizerInfo and
SITargetLowering. NFCI.
Lower formal arguments and returns for functions with the
`amdgpu_cs_chain` and `amdgpu_cs_chain_preserve` calling conventions:
* Put `inreg` arguments into SGPRs, starting at s0, and other arguments
into VGPRs, starting at v8. No arguments should end up on the stack, if
we don't have enough registers we should error out.
* Lower the return (which is always void) as an S_ENDPGM.
* Set the ScratchRSrc register to s48:51, as described in the docs.
* Set the SP to s32, matching amdgpu_gfx. This might be revisited in a
future patch.
Differential Revision: https://reviews.llvm.org/D153517
