No pre-rasterization stage writes Layer: vertex layer exports are
ignored, so the first layer is used and the render target index field
of the packed ancillary word is 0. The lowering read the Layer builtin
for it instead. AMD's Windows driver drops the color writes of a
fragment shader that consumes an unwritten Layer, which made
agc_driver_relative_ancillary fail on AMD hardware (#4800); lavapipe
returns 0 there.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
main reads target.vertexSubgroups at request version 18 since #4470, so
reading the pixel primitive class at 18 as well read a version 18
request written by main one byte short. The class is now written and
read at version 19. agc_shader_memory loads a version 18 request as
main writes it, and it fails with "truncated data" when the class is
read at 18.
The composed word no longer reads the Layer builtin for bits 16-28.
Draws render to a single layer and guest layer exports are ignored, so
no stage writes Layer, and AMD's Windows driver drops the writes of a
fragment shader that reads it unwritten (#4800). The field is the
constant 0 and pixel_ancillary checks that the composed program has no
Layer read. The debt entry names the bits that have no source and are
assumed zero (2-7, 12-15, 29-31), and says that a change which makes
draws export a layer must restore the read.
The relative-ancillary test expected the whole-word read through
v_movrels to be refused, which was main's behaviour before the word was
composed. It now converts that read to float and exports it: the
composed word of a triangle draw is 2 (primitive class 2, sample 0,
layer 0), so the pixel is 255, with and without the implicit position
inputs in front of the ancillary VGPR. TechnicalDebt's relative
addressing entry no longer says that whole-word uses throw.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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>
image_sample_c on an 8-bit UNORM T# returns 0 for every compare
function on gfx1035, as on 8-bit sRGB (measured on the hardware oracle
in the review of #3438), but the emulated comparison still compared the
red channel. 8, 8_8 and 8_8_8_8 UNORM now return 0 like 8-bit sRGB.
Every texel comparison of those formats is 0, so a bilinear cube
without DISABLE_CUBE_WRAP and an anisotropic S# cannot change the
result; both are accepted for them, as the cube already was for 8-bit
sRGB. Other formats keep both refusals.
The test rows that check real comparisons move to 16_16 UNORM.
LeandroLP23
Dean Galvin
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