SPV: Don't add clip/cull distance capabilities unless used.

These capabalities were added on declaration of the members, but
that is considered too aggressive, as those members are automatically
declared in some shaders that don't use them.  Now, actual access
is needed to make the capabalities be declared.

SPIRV/GlslangToSpv.cpp

@@ -109,7 +109,7 @@ public:
 
 protected:
     spv::Decoration TranslateInterpolationDecoration(const glslang::TQualifier& qualifier);
-    spv::BuiltIn TranslateBuiltInDecoration(glslang::TBuiltInVariable);
+    spv::BuiltIn TranslateBuiltInDecoration(glslang::TBuiltInVariable, bool member);
     spv::ImageFormat TranslateImageFormat(const glslang::TType& type);
     spv::Id createSpvVariable(const glslang::TIntermSymbol*);
     spv::Id getSampledType(const glslang::TSampler&);
@@ -122,6 +122,7 @@ protected:
     int getArrayStride(const glslang::TType& arrayType, glslang::TLayoutPacking, glslang::TLayoutMatrix);
     int getMatrixStride(const glslang::TType& matrixType, glslang::TLayoutPacking, glslang::TLayoutMatrix);
     void updateMemberOffset(const glslang::TType& structType, const glslang::TType& memberType, int& currentOffset, int& nextOffset, glslang::TLayoutPacking, glslang::TLayoutMatrix);
+    void declareClipCullCapability(const glslang::TTypeList& members, int member);
 
     bool isShaderEntrypoint(const glslang::TIntermAggregate* node);
     void makeFunctions(const glslang::TIntermSequence&);
@@ -393,7 +394,7 @@ spv::Decoration TranslateNoContractionDecoration(const glslang::TQualifier& qual
 }
 
 // Translate glslang built-in variable to SPIR-V built in decoration.
-spv::BuiltIn TGlslangToSpvTraverser::TranslateBuiltInDecoration(glslang::TBuiltInVariable builtIn)
+spv::BuiltIn TGlslangToSpvTraverser::TranslateBuiltInDecoration(glslang::TBuiltInVariable builtIn, bool member)
 {
     switch (builtIn) {
     case glslang::EbvPointSize:
@@ -410,12 +411,20 @@ spv::BuiltIn TGlslangToSpvTraverser::TranslateBuiltInDecoration(glslang::TBuiltI
         }
         return spv::BuiltInPointSize;
 
+    // These *Distance capabilities logically belong here, but if the member is declared and
+    // then never used, consumers of SPIR-V prefer the capability not be declared.
+    // They are now generated when used, rather than here when declared.
+    // Potentially, the specification should be more clear what the minimum
+    // use needed is to trigger the capability.
+    //
     case glslang::EbvClipDistance:
-        builder.addCapability(spv::CapabilityClipDistance);
+        if (! member)
+            builder.addCapability(spv::CapabilityClipDistance);
         return spv::BuiltInClipDistance;
 
     case glslang::EbvCullDistance:
-        builder.addCapability(spv::CapabilityCullDistance);
+        if (! member)
+            builder.addCapability(spv::CapabilityCullDistance);
         return spv::BuiltInCullDistance;
 
     case glslang::EbvViewportIndex:
@@ -926,6 +935,10 @@ bool TGlslangToSpvTraverser::visitBinary(glslang::TVisit /* visit */, glslang::T
             } else {
                 // normal case for indexing array or structure or block
                 builder.accessChainPush(builder.makeIntConstant(index));
+
+                // Add capabilities here for accessing clip/cull distance
+                if (node->getLeft()->getType().isStruct() && ! node->getLeft()->getType().isArray())
+                    declareClipCullCapability(*node->getLeft()->getType().getStruct(), index);
             }
         }
         return false;
@@ -1919,7 +1932,7 @@ spv::Id TGlslangToSpvTraverser::convertGlslangToSpvType(const glslang::TType& ty
                         builder.addMemberDecoration(spvType, member, spv::DecorationMatrixStride, getMatrixStride(glslangType, explicitLayout, subQualifier.layoutMatrix));
 
                     // built-in variable decorations
-                    spv::BuiltIn builtIn = TranslateBuiltInDecoration(glslangType.getQualifier().builtIn);
+                    spv::BuiltIn builtIn = TranslateBuiltInDecoration(glslangType.getQualifier().builtIn, true);
                     if (builtIn != spv::BadValue)
                         addMemberDecoration(spvType, member, spv::DecorationBuiltIn, (int)builtIn);
                 }
@@ -2172,6 +2185,14 @@ void TGlslangToSpvTraverser::updateMemberOffset(const glslang::TType& /*structTy
     nextOffset = currentOffset + memberSize;
 }
 
+void TGlslangToSpvTraverser::declareClipCullCapability(const glslang::TTypeList& members, int member)
+{
+    if (members[member].type->getQualifier().builtIn == glslang::EbvClipDistance)
+        builder.addCapability(spv::CapabilityClipDistance);
+    if (members[member].type->getQualifier().builtIn == glslang::EbvCullDistance)
+        builder.addCapability(spv::CapabilityCullDistance);
+}
+
 bool TGlslangToSpvTraverser::isShaderEntrypoint(const glslang::TIntermAggregate* node)
 {
     // have to ignore mangling and just look at the base name
@@ -3936,7 +3957,7 @@ spv::Id TGlslangToSpvTraverser::getSymbolId(const glslang::TIntermSymbol* symbol
     }
 
     // built-in variable decorations
-    spv::BuiltIn builtIn = TranslateBuiltInDecoration(symbol->getQualifier().builtIn);
+    spv::BuiltIn builtIn = TranslateBuiltInDecoration(symbol->getQualifier().builtIn, false);
     if (builtIn != spv::BadValue)
         addDecoration(id, spv::DecorationBuiltIn, (int)builtIn);
 

Test/baseResults/spv.150.geom.out

@@ -9,7 +9,6 @@ Linked geometry stage:
 
                               Capability Geometry
                               Capability GeometryPointSize
-                              Capability ClipDistance
                               Capability GeometryStreams
                1:             ExtInstImport  "GLSL.std.450"
                               MemoryModel Logical GLSL450

Test/baseResults/spv.430.vert.out

@@ -10,7 +10,6 @@ Linked vertex stage:
 // Id's are bound by 66
 
                               Capability Shader
-                              Capability ClipDistance
                1:             ExtInstImport  "GLSL.std.450"
                               MemoryModel Logical GLSL450
                               EntryPoint Vertex 4  "main" 12 23 34 38 41 42 62 65

Test/baseResults/spv.bool.vert.out

@@ -10,8 +10,6 @@ Linked vertex stage:
 // Id's are bound by 49
 
                               Capability Shader
-                              Capability ClipDistance
-                              Capability CullDistance
                1:             ExtInstImport  "GLSL.std.450"
                               MemoryModel Logical GLSL450
                               EntryPoint Vertex 4  "main" 24

Test/baseResults/spv.matFun.vert.out

@@ -10,7 +10,6 @@ Linked vertex stage:
 // Id's are bound by 103
 
                               Capability Shader
-                              Capability ClipDistance
                1:             ExtInstImport  "GLSL.std.450"
                               MemoryModel Logical GLSL450
                               EntryPoint Vertex 4  "main" 76 81