This PR resolved the following issues:
(1) There are rare but possible cases when there are bitcasts between
pointers intertwined in a sophisticated way with loads, stores, function
calls and other instructions that are part of type deduction. In this
case we must account for inserted bitcasts between pointers rather than
just ignore them.
(2) Null pointers have the same constant representation but different
types. Type info from Intrinsic::spv_track_constant() refers to the
opaque (untyped) pointer, so that each MF/v-reg pair would fall into the
same Const record in Duplicate Tracker and would be represented by a
single OpConstantNull instruction, unless we use precise pointee type
info. We must be able to distinguish one constant (null) pointer from
another to avoid generating invalid code with inconsistent types of
operands.
Goals of the PR are:
* to ensure that correct types are applied to virtual registers which
were used as return values in call lowering. A reproducer is attached as
a new test case, before the PR it fails because spirv-val considers
output invalid due to wrong result/operand types in OpPhi's;
* improve type inference by speeding up postprocessing of types: by
limiting iterations by checking what remains to process, and processing
each instruction just once for any number of operands with uncomplete
types;
* improve type inference by more accurate work with uncomplete types
(pass uncomplete property to dependent operands, ensure consistency of
uncomplete-types data structure);
* change processing order and add traversing of PHI nodes when type
inference apply instructions results to specify/update/cast operands
type (fixes an issue with OpPhi's result type mismatch with operand
types).
