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vkd3d-shader/ir: Introduce a simple control flow graph structurizer.

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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.
This commit is contained in:
Giovanni Mascellani
2024-01-16 23:56:43 +01:00
committed by Alexandre Julliard
parent 19aef21369
commit 51f13391e6
Notes: Alexandre Julliard 2024-02-06 23:42:19 +01:00 
Approved-by: Giovanni Mascellani (@giomasce)
Approved-by: Conor McCarthy (@cmccarthy)
Approved-by: Henri Verbeet (@hverbeet)
Approved-by: Alexandre Julliard (@julliard)
Merge-Request: https://gitlab.winehq.org/wine/vkd3d/-/merge_requests/607
8 changed files with 209 additions and 68 deletions
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tests/hlsl/for.shader_test
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@@ -54,7 +54,7 @@ float4 main(float tex : texcoord) : sv_target
[test]
uniform 0 uint4 10 0 0 0
todo(sm>=6) draw quad
draw quad
probe ( 0, 0, 159, 480) rgba (10.0, 35.0, 0.0, 0.0)
probe (161, 0, 479, 480) rgba (10.0, 38.0, 0.0, 0.0)
probe (481, 0, 640, 480) rgba ( 5.0, 10.0, 0.0, 0.0)