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Shader: test a wave mask consumed as a per-lane predicate at the lane bit (#465)

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* Shader: read a wave mask consumed as a per-lane predicate at the lane bit

A VCC/EXEC wave mask consumed as a per-lane predicate (the VCndmask
condition, a VCC/EXEC branch, or the derived _vcc/_exec bool) was tested in
single-lane emulation with a whole-word non-zero test (IsNotZero64) instead
of the current lane's bit. That is correct for comparison results (only the
lane's own bit is ever set) but wrong for bitwise-complement wave-mask idioms
(S_NOT / S_ORN2 / S_ANDN2 / S_NAND / S_NOR), which set the unused upper 63
bits: a whole-word test then reports the lane active even when its bit is
clear.

Unity's PostProcessing NaN killer does exactly this: per channel it computes
isNaN = NLT AND NGT AND NEQ (against 0), then combines the channels as
anyNaN OR NOT(v3-is-finite) via S_ORN2_B64. The complement set the upper mask
bits, so every valid pixel read as NaN and was replaced with 0, zeroing the
whole HDR scene before Bloom/Uber/tonemap. The 3D scene therefore rendered
black behind the menu while the UI survived. Extract the current lane's bit in
both single-lane and subgroup modes so IsWaveMaskActive matches the hardware.

Fixes Superliminal (PPSA06084) black 3D scene: the storage room now renders
behind the menu with natural exposure and no forced values.

(cherry picked from commit 7af6f4b6f314fe302619c0d44f4db00971c5bf24)

* test: wave-mask predicate is tested at the current lane bit

Regression test for the wave-mask lane-bit fix. Compiles a shader that
writes VCC at run time (V_CMP_EQ_F32) and asserts the emitted SPIR-V tests
the wave mask at the current lane's bit (mask & lane_bit) rather than with a
whole-word non-zero test. Fails against the previous IsNotZero64(mask) path,
which zeroed complement wave-mask idioms (S_ORN2/S_NOT, e.g. Unity's NaN
killer) across every lane.
This commit is contained in:
kuba
2026-07-20 13:18:20 +02:00
committed by GitHub
parent bb3318a503
commit 20eda4443c
2 changed files with 153 additions and 3 deletions
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src/SharpEmu.ShaderCompiler.Vulkan/Gen5SpirvTranslator.cs
+13 -3
View File
@@ -5290,10 +5290,20 @@ public static partial class Gen5SpirvTranslator
UInt(0x108));
}
// A wave-mask SGPR (VCC/EXEC) consumed as a per-lane predicate — the
// condition of VCndmask, a VCC/EXEC branch, or the derived _vcc/_exec
// bool — must be tested at the CURRENT lane's bit, exactly as the
// hardware does, not as "the 64-bit value is non-zero". The two coincide
// for comparison results (only the lane's own bit is ever set), so the
// single-lane path historically used a cheaper whole-word non-zero test.
// But bitwise-complement wave-mask idioms (S_NOT/S_ORN2/S_ANDN2/S_NAND/
// S_NOR on a 64-bit mask) set the unused upper 63 bits; a whole-word test
// then reports "lane active" even when this lane's bit is clear. Unity's
// PostProcessing NaN killer does exactly this (`anyNaN | ~allFinite`),
// which made every valid pixel read as NaN and get replaced with 0 —
// zeroing the whole scene before tonemap. Extract the lane bit always.
private uint IsWaveMaskActive(uint mask) =>
_subgroupInvocationIdInput == 0
? IsNotZero64(mask)
: IsCurrentLaneSet(mask);
IsCurrentLaneSet(mask);
private uint IsCurrentLaneSet(uint mask) =>
IsNotZero64(