With FP16_OVFL=1 the hardware writes an f16 result that would round to
infinity as the largest finite value of that sign, unless a source
operand is infinite. v_div_fixup_f16 keeps the infinity it writes for a
zero denominator or an infinite numerator. Measured on RDNA2 (gfx1036)
at IEEE=0 and IEEE=1 with f16 denormals kept and flushed.
Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Without VK_KHR_fragment_shader_barycentric the recompiler dropped
v_interp_p1_f32 and made v_interp_p2_f32 read the attribute Vulkan
interpolated, but never wrote the I/J VGPRs: a pixel shader that read
them for anything else got 0, and v_interp_mov_f32 of P10/P20 (or P0 of
an interpolated input) needed PerVertexKHR and failed pipeline
validation.
The fallback translation now loads the I/J VGPRs and marks v_interp_p1
and v_interp_p2 with witnesses. After the front-end simplification
(SSA, folding, DCE, read-lane and masked-select elimination),
HostInterpolationChecker requires every p2 to read its J, and its p1's
I, from a barycentric of the parameter's kind, every p1 result to reach
only the matching p2 (through a write masked by the p2's EXEC, whose
inactive lanes keep the old register), no parameter read as raw
vertices and no slot shared by different interpolations. It then
lowers the witnesses to the host-interpolated attribute as before,
reruns DCE and masked-select elimination, and accepts the program only
when no barycentric read remains, so reusing the I/J VGPRs after
interpolating keeps host interpolation and the previous SPIR-V. Any other
program is translated with the barycentric path and marked as emulated:
its barycentrics become vec3 inputs (NoPerspective for the linear
weights) and its per-vertex parameters flat vec4[3] inputs, placed in
the free locations by LayoutBarycentricEmulation. The driver then
inserts a generated geometry stage between the vertex and fragment
shaders that copies the position and parameters, writes the one-hot
weights of each vertex and the three vertices' parameter values, so the
rasterizer interpolates the same weights the extension provides.
The stage needs geometryShader and a vertex shader before it;
tessellation, mesh and rect-list pipelines, other primitive types and
interfaces beyond 32 locations or the device's geometry limits throw.
CompiledShaderArtifact carries the emulation (shader disk cache format 21).
Hardware snaps window corners to 1/256 pixel before interpolating
(measured by yahya308 on an RTX 4070 Laptop and a Radeon 780M in #1547);
lavapipe snaps only for coverage (lp_rast.h FIXED_ORDER 8), so the test
accepts either reference per pixel at the original 1e-4 margin.
Sources:
- v_interp_p1_f32/v_interp_p2_f32/v_interp_mov_f32 semantics (P0,
P10, P20, I/J): AMD RDNA2 ISA, "Parameter Interpolation".
- BaryCoordKHR/BaryCoordNoPerspKHR weights and PerVertexKHR vertex order:
SPV_KHR_fragment_shader_barycentric, VK_KHR_fragment_shader_barycentric.
- Geometry shader triangle input order and provoking vertex: Vulkan
specification, "Primitive Topologies" and "Geometry Shading".
- Interpolation decorations decided by the fragment input: Vulkan
specification, "Interpolation Decorations".
- lavapipe interpolation: Mesa src/gallium/drivers/llvmpipe/lp_rast.h
(FIXED_ORDER 8), lp_setup_tri.c (subpixel_snap for coverage only),
lp_state_setup.c (init_args, plane setup from float positions).
Measured on RDNA2 in #697: v_interp_p1ll_f16 and v_interp_p1lv_f16 are a
fused multiply-add rounded once to f32, and v_interp_p2_f16 rounds the exact
P20 * J + S2 once to f16. The separate multiply and add matched about 85% and
4% of the measured rows.
Both steps now use FPInterpolateF32 and FPInterpolateF16: the f16 delta times
the f32 coordinate is exact in f64, the sum is rounded to odd and then once to
nearest even at the target precision, so no driver can split or reround it.
Infinite and NaN operands take the unbounded f64 result.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Decode the three VOP3 16-bit interpolation instructions (attribute, channel
and high-half select in the src0 field, the I/J VGPR in src1, P0 or the first
step's result in src2) and translate them with a new
GetInterpolationParameterF16 IR value. It reads the selected 16-bit half of
each vertex's parameter through VK_KHR_fragment_shader_barycentric, so P10 and
P20 are vertex differences rounded to f16; both steps are a multiply and an
add, as in the f32 forms.
An input in FP16_INTERP_MODE whose low half is defaulted is still declared at
its slot when its high half is read, and the high half takes its default from
USE_DEFAULT_ATTR1 and DEFAULT_VAL_ATTR1. Without barycentrics, on an input
without FP16_INTERP_MODE or on a pass-through input the instructions throw.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
SPI_PS_INPUT_ENA/ADDR with PERSP_CENTROID (bit 2) or LINEAR_CENTROID
(bit 6) was rejected; PPSA21564 binds 0x326 (perspective center and
centroid, linear center, POS_X/Y).
The PS input VGPR layout now follows the hardware rule: SPI_PS_INPUT_ADDR
places every input it names in SPI order (two VGPRs per I/J pair, three
for the pull model, one otherwise), loaded or not, and ENA & ADDR selects
the loaded ones. ShaderPixelStageInfo carries inputAddr (replacing
perspectiveCenterVgpr) plus perspectiveCentroid and linearCentroid; the
recompiler places each loaded input with PixelInputVgpr. This also fixes
the system inputs, which were always written from v0 (psSystemInputBase
was never set), so POS_X overwrote the center I in any draw with
barycentrics enabled.
Draws are rasterized single-sampled, where the centroid is the pixel
center: with fragment barycentrics the centroid pairs carry the center
barycentrics (BaryCoordKHR for perspective; the linear center and
centroid pairs now get BaryCoordNoPerspKHR).
NoPerspective was decided for every parameter by one flag (LINEAR_CENTER
loaded). v_interp_p2 now records whether it reads the J of a linear or a
perspective pair, and a parameter is NoPerspective when it is read
through a linear pair; parameters read through neither keep the old
rule. A parameter read through both kinds of pair throws. Only pixel
stages consult this.
The request serializer moves to version 5 (older requests read back with
their loaded inputs as the layout); the cache key and the driver's draw
key compare and hash the new fields. The unsupported-input error names
ENA and ADDR.
Achraf Reyani
ale
russhil
Adrià Franch
Daan Dehing
boykopovar
SamG-Coder
Dean Galvin