Work around missing feature from GLSL. Normally we can emit a global
invariant gl_Position; and call it a day, but it does not work for mesh
shaders it seems. Declaring invariance inside an explicit IO block works
fine on the other hand ...
Handling native array types is not really feasible since we need to fuse
the variable declaration with the type declaration.
This is feasible in something like variable_decl, but for plain SSA
pointers, this breaks down.
Similar concern as access chains. Objects that we cannot lower to
temporaries must implicitly access all expression dependencies when they
are themselves accessed.
Undef values may be of struct type and may be used in constants.
Therefore, they must be interleaved with constants and types.
Fixes the rest of the Vulkan CTS test
`dEQP-VK.spirv_assembly.instruction.compute.opundef.undefined_spec_constant_composite`.
(Please excuse the churn in the reference output; it's an inevitable
result of this change.)
Speculate that we can modify the SSA value in-place. As long as it is
not used after the modify, this is fine.
Also need to make sure we don't attempt to RMW something that is
impossible to modify.
GLSL and RelaxedPrecision are quite different in what they affect.
RelaxedPrecision affects operations, while this is merely implied in
GLSL based on inputs.
This leads to situations where we have to promote mediump inputs to
highp, and the simplest approach is to force highp temporaries for
inputs which are consumed in a highp context. For completeness, we also
demote RelaxedPrecision inputs to mediump variables.
PHI is handled by copying the PHI into a temporary.
We have to be very careful with hoisted temporaries, since the child
temporary will not be analyzed up-front. We inherit the hoisted-ness
state and emit the hoisted child temporary as necessary. When faking the
temporaries with OpCopyObject, we make sure to block any variable
hoisting.
Hoisting children of PHI variables is fine, since PHIs are not hoisted with
the same framework as other temporaries.
Just like we try to fixup struct names for block types, inner structs
can be "anonymous" structs. HLSL codegen from DXC tends to emit this,
and emitting dummy struct names tends to break GL linkage on some
drivers.
Makes codegen from typical D3D emulation SPIR-V more readable.
Also makes cross compilation with NotEqual more sensible.
It's very rare to actually need the strict NaN-checks in practice.
Also, glslang now emits UnordNotEqual by default it seems, so give up
trying to assume OrdNotEqual. Harmonize for UnordNotEqual as the sane
default.
