The old method of using a different unpacked matrix type doesn't work
for scalar alignment. It certainly wouldn't have any effect for a square
matrix, since the number of columns and rows are the same. So now we'll
store them as arrays of packed vectors.
Relaxed block layout relaxed the restrictions on vector alignment,
allowing them to be aligned on scalar boundaries. Scalar block layout
relaxes this further, allowing *any* member to be aligned on a scalar
boundary. The requirement that a vector not improperly straddle a
16-byte boundary is also relaxed.
I've also added a test showing that `std430` layout works with UBOs.
I'm troubled by the dual meaning of the `Packed` extended decoration. In
some instances (struct, `float[]`, and `vec2[]` members), it actually
means the exact opposite, that the member needs extra padding. This is
especially problematic for `vec2[]`, because now we need to distinguish
the two cases by checking the array stride. I wonder if this should
actually be split into two decorations.
There is a case where we can deduce a for/while loop, but the continue
block is actually very painful to deal with, so handle that case as
well. Removes an exceptional case.
MSL prior to 2.2 doesn't support these natively in any stage but
compute. But, we can (assuming no threads were terminated prematurely)
get their values with some creative uses of the
`simd_prefix_exclusive_sum()` and `simd_sum()` functions.
Also, fix a missing `to_expression()` with `BuiltInSubgroupEqMask`.
For KhronosGroup/MoltenVK#629.
This is needed to support `VK_KHR_multiview`, which is in turn needed
for Vulkan 1.1 support. Unfortunately, Metal provides no native support
for this, and Apple is once again less than forthcoming, so we have to
implement it all ourselves.
Tessellation and geometry shaders are deliberately unsupported for now.
The problem is that the current implementation encodes the `ViewIndex`
as part of the `InstanceIndex`, which in the SPIR-V environment at least
only exists in the vertex shader. So we need to work out a way to pass
the view index along to the later stages.
This implementation runs vertex shaders for all views up to the highest
bit set in the view mask, even those whose bits are clear. The fragments
for the inactive views are then discarded. Avoiding this is difficult:
calculating the view indices becomes far more complicated if we can only
run for those views which are set in the mask.
This is quite complex since we cannot flush Phi inside the case labels,
we have to do it outside by emitting a lot of manual branches ourselves.
This should be extremely rare, but we need to handle this case.
We used to use the Binding decoration for this, but this method is
hopelessly broken. If no explicit MSL resource remapping exists, we
remap automatically in a manner which should always "just work".
If we compile multiple times due to forced_recompile, we had
deferred_declaration = true while emitting function prototypes which
broke an assumption. Fix this by clearing out stale state before leaving
a function.
This is rather shaky, but we don't have many choices here except add a
lot of awkward and unintuitive options. Try to deduce this from OpSource
and fallback to heuristic.
There is a risk that we try to preserve a loop variable through multiple
iterations, even though the dominating block is inside a loop.
Fix this by analyzing if a block starts off by writing to a variable. In
that case, there cannot be any preservation going on. If we don't, pretend the
loop header is reading the variable, which moves the variable to an
appropriate scope.
In multiple-entry-point modules, we declared builtin inputs which were
not supposed to be used for that entry point.
Fix this, by being more strict when checking which builtins to emit.
