Metal will incorrectly discard fragments with side effects under
certain circumstances prematurely. The conditions are the following:
- Fragment will always be discarded after side effect operation
- Pre fragment depth fails
- Modifies depth value for a constant value in the fragment shader.
This constant value will also fail the depth test.
However, Metal will also discard the fragment even if it has
operations with side effects inside the fragment shader before the
discard operation.
Vulkan states the graphics pipeline to execute in the following
order:
- Pre fragment depth test (cannot discard here due to modifying
depth value in fragment shader)
- Fragment shader (where the depth is modified and fragment
discarded)
- Post fragment depth test
Therefore, we need to enforce fragment shader execution and not
let Metal discard the fragment before that for such cases. This
change adds an option to provide such utility.
Inner function calls can contain flow-control sensitive code.
In this case, the function call itself must inherit the
control-dependence.
Rarely happens in practice since optimized code with SSA tends to
inline.
This adds support for bindings which share the same DescriptorSet/Binding pair.
The motivating example is vkd3d, which uses overlapping arrays of resources to
emulate D3D12 descriptor tables. The generated MSL argument buffer only
includes the first resource (in this example 't0'):
struct spvDescriptorSetBuffer2
{
array<texture2d<float>, 499968> t0 [[id(0)]];
// Overlapping binding: array<texture3d<float>, 499968> t2 [[id(0)]];
};
When t2 is referenced, we cast the instantiated member:
float4 r1 = spvDescriptorSet2.t0[_79].sample(...);
float4 r2 = (*(constant array<texture3d<float>, 499968>*)&spvDescriptorSet2.t0)[_97].sample(...);
Comment claims we can't, but I tested a number of older Metal compilers (Xcode 8 targeting macOS 10.11, macOS 10.13 online compiler, Xcode 14 targeting iOS 8) and none of them had any issues with it
Somehow this hasn't been caught until now. Impressive.
We'll have to emit side effects in condition block to make this work,
which breaks loop conditionals.
Prevent cases where arrays that are globally defined constants are redeclared
on stack. On Intel macs, declaring a large, statically initialized
spvUnsafeArray on stack may cause an internal compiler error.
CompilerMSL:msl_options.texture_1D_as_2D emulates a Metal 1D texture
as a 2D texture in order to expand features available for 1D textures.
Support accessing such textures as 2D for atomic_compare_exchange_weak().
