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51f13391e6
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.
47 lines
749 B
Plaintext
47 lines
749 B
Plaintext
% The ternary operator works differently in sm6.
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% It now shortcuts, and is no longer per-component.
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[require]
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shader model >= 6.0
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[pixel shader]
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uniform float4 x;
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float4 main() : sv_target
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{
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return x.x ? x : x - 1;
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}
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[test]
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uniform 0 float4 2.0 3.0 4.0 5.0
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draw quad
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probe all rgba (2.0, 3.0, 4.0, 5.0)
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uniform 0 float4 0.0 10.0 11.0 12.0
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draw quad
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probe all rgba (-1.0, 9.0, 10.0, 11.0)
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[pixel shader]
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float4 f;
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float4 main() : sv_target
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{
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float f1 = 0.1, f2 = 0.2, f3;
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f3 = f.x ? (f1 = 0.5) + 0.2 : (f2 = 0.6);
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return float4(f1, f2, f3, 0.0);
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}
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[test]
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uniform 0 float4 1.0 0.0 0.0 0.0
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draw quad
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probe all rgba (0.5, 0.2, 0.7, 0.0)
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[pixel shader fail]
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float4 x, y, z;
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float4 main() : sv_target
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{
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return x ? y : z;
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}
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