[Fix, Test] (DirectGLES, ShaderTranspiler): synthesize the pass-through tessellation control stage ES requires

MobileGL/MG_Util/ShaderTranspiler/ShaderCompiler.cpp

@@ -598,6 +598,43 @@ namespace MobileGL {
                 return false;
             }
 
+            Bool ShaderCompiler::ModuleReadsLocatedInput(const Vector<Uint32>& spirv) {
+                if (spirv.empty()) {
+                    return false;
+                }
+                std::unique_ptr<spvtools::opt::IRContext> context = spvtools::BuildModule(
+                    SPV_ENV_VULKAN_1_1, MakeSpirvMessageConsumer("ModuleReadsLocatedInput"), spirv.data(),
+                    spirv.size());
+                if (!context) {
+                    return false;
+                }
+                // A LOCATION is exactly the property that separates a user-defined varying (or a
+                // per-patch input) from a built-in: gl_in, gl_TessCoord, gl_PatchVerticesIn,
+                // gl_PrimitiveID and the tessellation levels carry none, and every one of them is
+                // either forwarded by the pass-through or generated by the tessellator itself.
+                //
+                // Decided on the OpVariable's own Location decoration rather than on any
+                // built-in classification, for the reason DirectVulkan's
+                // ReflectPassthroughTessControlNeed records at length: gl_in is an ARRAY OF
+                // INTERFACE BLOCKS, and a member walk of one reads back as BuiltIn::Position for
+                // every member, so classifying by built-in would accept anything.
+                for (auto& variable : context->module()->types_values()) {
+                    if (variable.opcode() != spv::Op::OpVariable || variable.NumInOperands() < 1) {
+                        continue;
+                    }
+                    if (static_cast<spv::StorageClass>(variable.GetSingleWordInOperand(0)) !=
+                        spv::StorageClass::Input) {
+                        continue;
+                    }
+                    Bool located = false;
+                    context->get_decoration_mgr()->ForEachDecoration(
+                        variable.result_id(), static_cast<uint32_t>(spv::Decoration::Location),
+                        [&located](const spvtools::opt::Instruction&) { located = true; });
+                    if (located) return true;
+                }
+                return false;
+            }
+
             bool ShaderCompiler::DemoteFloat64ToFloat32(const Vector<Uint32>& inputBinary,
                                                         Vector<uint32_t>& outputBinary,
                                                         const bool enableSpirvValidation) {

MobileGL/MG_Util/ShaderTranspiler/ShaderCompiler.h

@@ -427,6 +427,19 @@ namespace MobileGL {
                 // module (see its header for the two operations that make it decline), which is
                 // what the backends report: no mobile driver can build such a module.
                 static Bool ModuleDeclaresFloat64(const Vector<Uint32>& spirv);
+
+                // True when the module declares an Input variable carrying a Location - i.e. a
+                // user-defined varying or a per-patch input, as opposed to a built-in.
+                //
+                // Asked of a TESSELLATION EVALUATION stage that has no control stage, to decide
+                // whether the pass-through control stage GL 4.6 core 11.2.2 describes can stand
+                // in for the missing one. That stage forwards gl_Position and nothing else, so a
+                // located input - which the vertex stage feeds today and which would stop
+                // arriving once a control stage sat in between - means the program has to be
+                // declined rather than fed an undefined varying. Same rule, same reasoning, as
+                // DirectVulkan's ReflectPassthroughTessControlNeed, which asks SPIRV-Reflect the
+                // identical question for the identical decision.
+                static Bool ModuleReadsLocatedInput(const Vector<Uint32>& spirv);
             };
         } // namespace ShaderTranspiler
     } // namespace MG_Util