To consolidate behavior of function mangling and limit the number of
places that ABI changes will need to be made, this switches the DirectX
target used for HLSL to use the Itanium ABI from the Microsoft ABI. The
Itanium ABI has greater flexibility in decisions regarding mangling of
new types of which we have more than a few yet to add.
One effect of this will be that linking library shaders compiled with
DXC will not be possible with shaders compiled with clang. That isn't
considered a terribly interesting use case and one that would likely
have been onerous to maintain anyway.
This involved adding a function to call all global destructors as the
Microsoft ABI had done.
This requires a few changes to tests. Most notably the mangling style
has changed which accounts for most of the changes. In making those
changes, I took the opportunity to harmonize some very similar tests for
greater consistency. I also shaved off some unneeded run flags that had
probably been copied over from one test to another.
Other changes effected by using the new ABI include using different
types when manipulating smaller bitfields, eliminating an unnecessary
alloca in one instance in this-assignment.hlsl, changing the way static
local initialization is guarded, and changing the order of inout
parameters getting copied in and out. That last is a subtle change in
functionality, but one where there was sufficient inconsistency in the
past that standardizing is important, but the particular direction of
the standardization is less important for the sake of existing shaders.
fixes#110736
HLSL constant sized array function parameters do not decay to pointers.
Instead constant sized array types are preserved as unique types for
overload resolution, template instantiation and name mangling.
This implements the change by adding a new `ArrayParameterType` which
represents a non-decaying `ConstantArrayType`. The new type behaves the
same as `ConstantArrayType` except that it does not decay to a pointer.
Values of `ConstantArrayType` in HLSL decay during overload resolution
via a new `HLSLArrayRValue` cast to `ArrayParameterType`.
`ArrayParamterType` values are passed indirectly by-value to functions
in IR generation resulting in callee generated memcpy instructions.
The behavior of HLSL function calls is documented in the [draft language
specification](https://microsoft.github.io/hlsl-specs/specs/hlsl.pdf)
under the Expr.Post.Call heading.
Additionally the design of this implementation approach is documented in
[Clang's
documentation](https://clang.llvm.org/docs/HLSL/FunctionCalls.html)
Resolves#70123
