For arguments that are not expected to be materialized with
G_CONSTANT, this was emitting predicates which could never match. It
was first adding a meaningless LLT check, which would always fail due
to the operand not being a register.
Infer the cases where a literal should check for an immediate operand,
instead of a register This avoids needing to invent a special way of
representing timm literal values.
Also handle immediate arguments in GIM_CheckLiteralInt. The comments
stated it handled isImm() and isCImm(), but that wasn't really true.
This unblocks work on the selection of all of the complicated AMDGPU
intrinsics in future commits.
Matt Arsenault