[NVPTX] Convert calls to indirect when call signature mismatches function signature (#107644)

When there is a function signature mismatch between a call
instruction and the callee, lower the call to an indirect call. The
current behavior is to produce direct calls that may or may not be
valid PTX. Consider the following example with mismatching return
types:

```
%struct.1 = type <{i64}>
%struct.2 = type <{i64}>
declare %struct.1 @callee()
...
%call1 = call %struct.2 @callee()
%call2 = call i64 @callee()
```

The return type of `callee` in PTX is `.b8 _[8]`. The return type of
`%call1` will be the same and so the PTX has no problems. The return
type of `%call2` will be `.b64`, so the types will not match and PTX
will be unacceptable to ptxas. This despite all the types having the
same size. The same is true for mismatching parameter types.

If we instead convert these calls to indirect calls, we will generate
functional PTX when the types have the same size. If they do not have
the same size then the PTX will likely be incorrect, though this will not
necessarily be caught by ptxas. Also, even if the sizes are the same, if
the types differ then it is technically undefined behavior. This change
allows for more flexibility in the bitcode that can be lowered to
functioning PTX, at the cost of sometimes producing PTX that is less
clearly wrong than it would have been previously (i.e. incorrect indirect
calls are not as obviously wrong as incorrect direct calls). We consider
it okay to generate PTX with undefined behavior as the behavior of
calls with mismatching types is not explicitly defined.

0 files changed, 0 insertions, 0 deletions