A packed ancillary word that still reaches an export, or any other read
the masked-select pass cannot drop, no longer stops the recompile. After
that pass every remaining use gets the composed word: the primitive class
at bits 0-1, SampleId at bits 8-11 and Layer at bits 16-28, with every
other bit zero. Those lanes do export the ancillary VGPR on the console,
so the word has to be right, not just present.
The primitive class (0 point, 1 line, 2 triangle, 3 rectangle) comes from
the draw. RasterPrimitiveOf maps rect lists to 3, line lists on the vertex
path to 1 and everything else the driver accepts to 2, because its
geometry and tessellation paths only output triangles. It reaches the
shader as pipeline specialization constant 8233, the way dual-source
blending does: a request field that is folded into the specialized
module and is part of the result memo, the draw key and the serialized
request (version 17).
Only shaders that read the class pay for it. ShaderInfo records the read
(disk cache format 28), and only those shaders put the class in their
module key, so a shader that reads just the sample or layer field keeps
one module for every primitive class. The draw sets the class only when
the pixel shader loads the ancillary VGPR, so other draws keep the draw
cache entries they have today.
The VRS rates (bits 2-5) and the eye id (bit 7) are 0 because the driver
supports neither VRS nor multiview. SampleId is 0 because the driver
rejects MSAA and per-sample shading, and Layer is 0 while it ignores
vertex layer exports. TechnicalDebt.md records the layout sources and
these assumptions.
Tests:
- pixel_ancillary builds an export to target 0 whose two channels select
between a packed value and a phi carrying the word. It checks the word
for each primitive class, sample and layer, checks that the three
shapes the masked-select pass keeps now compile with the composed word,
and that a program whose select the pass drops reads no class.
- agc_driver_pixel_ancillary_word exports the word from a draw and reads
back 2, 3 and 1 for triangle, rectangle and line. A shader that reads
only the sample field shares one module across the classes, and the
whole-word shader gets one per class. It also checks RasterPrimitiveOf.
- agc_shader_memory covers the version 17 round trip, and
agc_shader_disk_cache the new flag.
Both ancillary tests fail with the old refusal when the composition is
disabled.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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