On shader_test files, now resources should be declared this way:
[texture n] -> [srv n]
[srv buffer n] -> [srv n]
[uav n] -> [uav n]
[uav buffer n] -> [uav n]
[vertex buffer n] -> [vb n]
[render target n] -> [rtv n]
The dimension (buffer or 2D) is now specified as an additional parameter
in the "size" directive:
For 2D resources:
size (n, m) -> size (2d, n, m)
For buffers:
size (n, 1) -> size (buffer, n)
If in the same shader_test file we have both a [buffer uav n] and a
[uav n] with the same slot "n", we want the last one to override the
first one instead of passing both resources to the backends.
Same for [buffer srv n] and [texture n] after we introduce SRV buffers.
For temporary registers, SM1-SM3 integer types are internally
represented as floating point, so, in order to perform a cast
from ints to floats we need a mere MOV.
For constant integer registers "iN" there is no operation for casting
from a floating point register to them. For address registers "aN", and
the loop counting register "aL", vertex shaders have the "mova" operation
but we haven't used these registers in any way yet.
We probably would want to introduce these as synthetic variables
allocated in a special register set. In that case we have to remember to
use MOVA instead of MOV in the store operations, but they shouldn't be src
or dst of CAST operations.
Regarding constant integer registers, in some shaders, constants are
expected to be received formatted as an integer, such as:
int m;
float4 main() : sv_target
{
float4 res = {0, 0, 0, 0};
for (int k = 0; k < m; ++k)
res += k;
return res;
}
which compiles as:
// Registers:
//
// Name Reg Size
// ------------ ----- ----
// m i0 1
//
ps_3_0
def c0, 0, 1, 0, 0
mov r0, c0.x
mov r1.x, c0.x
rep i0
add r0, r0, r1.x
add r1.x, r1.x, c0.y
endrep
mov oC0, r0
but this only happens if the integer constant is used directly in an
instruction that needs it, and as I said there is no instruction that
allows converting them to a float representation.
Notice how a more complex shader, that performs operations with this
integer variable "m":
int m;
float4 main() : sv_target
{
float4 res = {0, 0, 0, 0};
for (int k = 0; k < m * m; ++k)
res += k;
return res;
}
gives the following output:
// Registers:
//
// Name Reg Size
// ------------ ----- ----
// m c0 1
//
ps_3_0
def c1, 0, 0, 1, 0
defi i0, 255, 0, 0, 0
mul r0.x, c0.x, c0.x
mov r1, c1.y
mov r0.y, c1.y
rep i0
mov r0.z, r0.x
break_ge r0.y, r0.z
add r1, r0.y, r1
add r0.y, r0.y, c1.z
endrep
mov oC0, r1
Meaning that the uniform "m" is just stored as a floating point in
"c0", the constant integer register "i0" is just set to 255 (hoping
it is a high enough value) using "defi", and the "break_ge"
involving c0 is used to break from the loop.
We could potentially use this approach to implement loops from SM3
without expecting the variables being received as constant integer
registers.
According to the D3D documentation, for SM1-SM3 constant integer
registers are only used by the 'loop' and 'rep' instructions.
These tests should actually compile and run in SM1, which is possible
if we pass the int and uint uniforms in the expected IEEE 754 float
format for SM1 shaders.
Also, bools should be passed as 1.0f or 0.0f to SM1.
When the "if" qualifier is added to a directive, the directive is
skipped if the shader->minimum_shader_model is not included in the
range.
This can be used on the "probe" directives for tests that have different
expected results on different shader models, without having to resort to
[require] blocks.
This test currently hit a Metal bug when run on Apple Silicon with
MoltenVK and fails. We don't have an easy way to mark shader runner
tests as buggy and we're not interested in tracking that bug anyway,
so I'm just working around it.
The structurizer is implemented along the lines of what is usually called
the "structured program theorem": the control flow is completely
virtualized by mean of an additional TEMP register which stores the
block index which is currently running. The whole program is then
converted to a huge switch construction enclosed in a loop, executing
at each iteration the appropriate block and updating the register
depending on block jump instruction.
The algorithm's generality is also its major weakness: it accepts any
input program, even if its CFG is not reducible, but the output
program lacks any useful convergence information. It satisfies the
letter of the SPIR-V requirements, but it is expected that it will
be very inefficient to run on a GPU (unless a downstream compiler is
able to devirtualize the control flow and do a proper convergence
analysis pass). The algorithm is however very simple, and good enough
to at least pass tests, enabling further development. A better
alternative is expected to be upstreamed incrementally.
Side note: the structured program theorem is often called the
Böhm-Jacopini theorem; Böhm and Jacopini did indeed prove a variation
of it, but their algorithm is different from what is commontly attributed
to them and implemented here, so I opted for not using their name.
These can be disassembled by D3DDisassemble() just fine, and perhaps
more importantly, shader model 1 vertex shaders do not require dcl_
instructions in Direct3D 8.
