6 files changed, 88 insertions, 16 deletions
diff --git a/source/slang/slang-emit-spirv.cpp b/source/slang/slang-emit-spirv.cpp
index 1b5747621..1a661920a 100644
--- a/source/slang/slang-emit-spirv.cpp
+++ b/source/slang/slang-emit-spirv.cpp
@@ -3461,17 +3461,6 @@ struct SPIRVEmitContext
             varInst,
             builtinVal
         );
-        
-        if (storageClass == SpvStorageClassInput ||
-            storageClass == SpvStorageClassOutput)
-        {
-            switch (builtinVal)
-            {
-            case SpvBuiltInPrimitiveId:
-                _maybeEmitInterpolationModifierDecoration(IRInterpolationMode::NoInterpolation, varInst);
-                break;
-            }
-        }
         m_builtinGlobalVars[key] = varInst;
         return varInst;
     }
@@ -5740,6 +5729,22 @@ struct SPIRVEmitContext
     }
 };
 
+bool isInstUsedInStage(SPIRVEmitContext& context, IRInst* inst, Stage s)
+{
+    auto* referencingEntryPoints = context.m_referencingEntryPoints.tryGetValue(inst);
+    if (!referencingEntryPoints)
+        return false;
+    for (auto entryPoint : *referencingEntryPoints)
+    {
+        if (auto entryPointDecor = entryPoint->findDecoration<IREntryPointDecoration>())
+        {
+            if (entryPointDecor->getProfile().getStage() == s)
+                return true;
+        }
+    }
+    return false;
+}
+
 SlangResult emitSPIRVFromIR(
     CodeGenContext*         codeGenContext,
     IRModule*               irModule,
@@ -5804,6 +5809,29 @@ SlangResult emitSPIRVFromIR(
         context.ensureInst(irEntryPoint);
     }
 
+    // Declare integral input builtins as Flat if necessary.
+    for (auto globalInst : context.m_irModule->getGlobalInsts())
+    {
+        if (globalInst->getOp() != kIROp_GlobalVar &&
+            globalInst->getOp() != kIROp_GlobalParam)
+            continue;
+        auto spvVar = context.m_mapIRInstToSpvInst.tryGetValue(globalInst);
+        if (!spvVar)
+            continue;
+        auto ptrType = as<IRPtrType>(globalInst->getDataType());
+        if (!ptrType)
+            continue;
+        auto addrSpace = ptrType->getAddressSpace();
+        if (addrSpace == SpvStorageClassInput)
+        {
+            if (isIntegralScalarOrCompositeType(ptrType->getValueType()))
+            {
+                if (isInstUsedInStage(context, globalInst, Stage::Fragment))
+                    context._maybeEmitInterpolationModifierDecoration(IRInterpolationMode::NoInterpolation, *spvVar);
+            }
+        }
+    }
+
     // Move forward delcared pointers to the end.
     do
     {
diff --git a/source/slang/slang-ir-glsl-legalize.cpp b/source/slang/slang-ir-glsl-legalize.cpp
index ca9367ea0..d2d09f45a 100644
--- a/source/slang/slang-ir-glsl-legalize.cpp
+++ b/source/slang/slang-ir-glsl-legalize.cpp
@@ -637,12 +637,13 @@ GLSLSystemValueInfo* getGLSLSystemValueInfo(
 
         if( kind == LayoutResourceKind::VaryingInput )
         {
-            name = "gl_SampleMaskIn[0]";
+            name = "gl_SampleMaskIn";
         }
         else
         {
-            name = "gl_SampleMask[0]";
+            name = "gl_SampleMask";
         }
+        arrayIndex = 0;
     }
     else if(semanticName == "sv_innercoverage")
     {
@@ -891,6 +892,7 @@ GLSLSystemValueInfo* getGLSLSystemValueInfo(
         //
 
         name = "gl_PositionPerViewNV[1]";
+        arrayIndex = 1;
 
 //            shared->requiresCopyGLPositionToPositionPerView = true;
     }
@@ -1594,7 +1596,12 @@ ScalarizedVal adaptType(
             return adaptType(builder, loaded, toType, fromType);
         }
         break;
-
+    case ScalarizedVal::Flavor::arrayIndex:
+        {
+            auto element = builder->emitElementExtract(val.irValue, as<ScalarizedArrayIndexValImpl>(val.impl)->index);
+            return adaptType(builder, element, toType, fromType);
+        }
+        break;
     default:
         SLANG_UNEXPECTED("unimplemented");
         UNREACHABLE_RETURN(ScalarizedVal());
@@ -1788,7 +1795,7 @@ ScalarizedVal getSubscriptVal(
 
             resultAdapter->val = getSubscriptVal(
                 builder,
-                elementType,
+                inputAdapter->actualType,
                 inputAdapter->val,
                 indexVal);
             return ScalarizedVal::typeAdapter(resultAdapter);
diff --git a/source/slang/slang-ir-spirv-legalize.cpp b/source/slang/slang-ir-spirv-legalize.cpp
index 5589510ed..b387a67f6 100644
--- a/source/slang/slang-ir-spirv-legalize.cpp
+++ b/source/slang/slang-ir-spirv-legalize.cpp
@@ -1934,7 +1934,7 @@ struct SPIRVLegalizationContext : public SourceEmitterBase
                 // After legalizing the control flow, we need to sort our blocks to ensure this is true.
                 sortBlocksInFunc(func);
             }
-
+            
             if (isInlinableGlobalInst(globalInst))
             {
                 for (auto use = globalInst->firstUse; use; use = use->nextUse)
diff --git a/tests/cross-compile/sv-coverage.slang b/tests/cross-compile/sv-coverage.slang
index 3bae3ea8a..b61530e7b 100644
--- a/tests/cross-compile/sv-coverage.slang
+++ b/tests/cross-compile/sv-coverage.slang
@@ -1,6 +1,7 @@
 // sv-coverage.slang
 
 //TEST:CROSS_COMPILE:-target spirv-assembly -entry main -stage fragment
+//TEST:SIMPLE(filecheck=CHECK):-target spirv -entry main -stage fragment -emit-spirv-directly
 
 float4 main(
 	in float4 color : COLOR,
@@ -8,6 +9,7 @@ float4 main(
 	out uint outputCoverage : SV_Coverage)
 	: SV_Target
 {
+    // CHECK: %gl_SampleMask = OpVariable %_ptr_Input__arr_int_int_1 Input
 	outputCoverage = inputCoverage ^ 1;
 	return color;
 }
diff --git a/tests/spirv/flat-builtin.slang b/tests/spirv/flat-builtin.slang
new file mode 100644
index 000000000..927c6d045
--- /dev/null
+++ b/tests/spirv/flat-builtin.slang
@@ -0,0 +1,12 @@
+//TEST:SIMPLE(filecheck=CHECK):-target spirv -emit-spirv-directly -entry main -stage fragment
+struct PerPrimitive {
+    int primitive_id : SV_PrimitiveID;
+    int layer : SV_RenderTargetArrayIndex;
+};
+
+// CHECK: OpDecorate %gl_PrimitiveID Flat
+// CHECK: OpDecorate %gl_Layer Flat
+[shader("fragment")]
+uint main(PerPrimitive data) : SV_Target {
+    return data.primitive_id + data.layer;
+}
+\ No newline at end of file
diff --git a/tests/spirv/primitive-id.slang b/tests/spirv/primitive-id.slang
new file mode 100644
index 000000000..8c354200b
--- /dev/null
+++ b/tests/spirv/primitive-id.slang
@@ -0,0 +1,23 @@
+//TEST:SIMPLE(filecheck=CHECK): -target spirv -emit-spirv-directly -entry main -stage mesh
+struct PerVertex {
+    float4 pos : SV_Position;
+};
+
+struct PerPrimitive {
+    uint32_t primitive_id : SV_PrimitiveID;
+    uint32_t layer : SV_RenderTargetArrayIndex;
+};
+
+// CHECK: %gl_PrimitiveID = OpVariable %_ptr_Output__arr_int_int_1 Output
+
+[shader("mesh")]
+[numthreads(1, 1, 1)]
+[outputtopology("triangle")]
+void main(out vertices PerVertex vertices[3], out indices uint3 triangles[1], out primitives PerPrimitive primitive_data[1]) {
+    SetMeshOutputCounts(3, 1);
+    
+    vertices[0].pos = vertices[1].pos = vertices[2].pos = 0;
+    triangles[0] = uint3(0, 1, 2);
+    primitive_data[0].primitive_id = 0;
+    primitive_data[0].layer = 0;
+}
+\ No newline at end of file