From d61f81374272c2abc34eecab19e916b979b08a55 Mon Sep 17 00:00:00 2001
From: Pankaj Mistry <63069047+pmistryNV@users.noreply.github.com>
Date: Fri, 5 Apr 2024 14:52:50 -0700
Subject: Add decoration PerPrimitiveEXT when a mesh output variable is
 decorated with PrimitiveID (#3895)

Fixes bug 3872
---
 source/slang/slang-emit-spirv.cpp | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

(limited to 'source/slang')

diff --git a/source/slang/slang-emit-spirv.cpp b/source/slang/slang-emit-spirv.cpp
index 942e089db..9f116a1e2 100644
--- a/source/slang/slang-emit-spirv.cpp
+++ b/source/slang/slang-emit-spirv.cpp
@@ -3827,6 +3827,7 @@ struct SPIRVEmitContext
                     // non-tessellation shader stages, and if so include a declaration of
                     // Geometry capability.
                     bool needGeometryCapability = true;
+                    bool needPerPrimitiveEXTDecoration = false;
                     if (entryPoints)
                     {
                         for (auto entryPoint : *entryPoints)
@@ -3835,9 +3836,13 @@ struct SPIRVEmitContext
                             {
                                 switch (entryPointDecor->getProfile().getStage())
                                 {
+                                case Stage::Mesh:
+                                    // For outputs decorated with PrimitiveID it must be decorated
+                                    // with PerPrimitiveEXT to comply with Vulkan validation rules
+                                    if (m_capabilities.contains(SpvCapabilityMeshShadingEXT))
+                                        needPerPrimitiveEXTDecoration = true;
                                 case Stage::Geometry:
                                 case Stage::Intersection:
-                                case Stage::Mesh:
                                 case Stage::Amplification:
                                 case Stage::AnyHit:
                                 case Stage::ClosestHit:
@@ -3851,7 +3856,14 @@ struct SPIRVEmitContext
                     }
                     if (needGeometryCapability)
                         requireSPIRVCapability(SpvCapabilityGeometry);
-                    return getBuiltinGlobalVar(inst->getFullType(), SpvBuiltInPrimitiveId);
+                    auto varInst = getBuiltinGlobalVar(inst->getFullType(), SpvBuiltInPrimitiveId);
+                    if (needPerPrimitiveEXTDecoration)
+                        emitOpDecorate(
+                            getSection(SpvLogicalSectionID::Annotations),
+                            nullptr,
+                            varInst,
+                            SpvDecorationPerPrimitiveEXT);
+                    return varInst;
                 }
                 else if (semanticName == "sv_rendertargetarrayindex")
                 {
-- 
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