1 //===- LowerABIAttributesPass.cpp - Decorate composite type ---------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file implements a pass to lower attributes that specify the shader ABI
10 // for the functions in the generated SPIR-V module.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "PassDetail.h"
15 #include "mlir/Dialect/SPIRV/IR/SPIRVDialect.h"
16 #include "mlir/Dialect/SPIRV/IR/SPIRVOps.h"
17 #include "mlir/Dialect/SPIRV/Transforms/Passes.h"
18 #include "mlir/Dialect/SPIRV/Transforms/SPIRVConversion.h"
19 #include "mlir/Dialect/SPIRV/Utils/LayoutUtils.h"
20 #include "mlir/Transforms/DialectConversion.h"
21 #include "llvm/ADT/SetVector.h"
22 
23 using namespace mlir;
24 
25 /// Creates a global variable for an argument based on the ABI info.
26 static spirv::GlobalVariableOp
27 createGlobalVarForEntryPointArgument(OpBuilder &builder, spirv::FuncOp funcOp,
28                                      unsigned argIndex,
29                                      spirv::InterfaceVarABIAttr abiInfo) {
30   auto spirvModule = funcOp->getParentOfType<spirv::ModuleOp>();
31   if (!spirvModule)
32     return nullptr;
33 
34   OpBuilder::InsertionGuard moduleInsertionGuard(builder);
35   builder.setInsertionPoint(funcOp.getOperation());
36   std::string varName =
37       funcOp.getName().str() + "_arg_" + std::to_string(argIndex);
38 
39   // Get the type of variable. If this is a scalar/vector type and has an ABI
40   // info create a variable of type !spv.ptr<!spv.struct<elementType>>. If not
41   // it must already be a !spv.ptr<!spv.struct<...>>.
42   auto varType = funcOp.getType().getInput(argIndex);
43   if (varType.cast<spirv::SPIRVType>().isScalarOrVector()) {
44     auto storageClass = abiInfo.getStorageClass();
45     if (!storageClass)
46       return nullptr;
47     varType =
48         spirv::PointerType::get(spirv::StructType::get(varType), *storageClass);
49   }
50   auto varPtrType = varType.cast<spirv::PointerType>();
51   auto varPointeeType = varPtrType.getPointeeType().cast<spirv::StructType>();
52 
53   // Set the offset information.
54   varPointeeType =
55       VulkanLayoutUtils::decorateType(varPointeeType).cast<spirv::StructType>();
56 
57   if (!varPointeeType)
58     return nullptr;
59 
60   varType =
61       spirv::PointerType::get(varPointeeType, varPtrType.getStorageClass());
62 
63   return builder.create<spirv::GlobalVariableOp>(
64       funcOp.getLoc(), varType, varName, abiInfo.getDescriptorSet(),
65       abiInfo.getBinding());
66 }
67 
68 /// Gets the global variables that need to be specified as interface variable
69 /// with an spv.EntryPointOp. Traverses the body of a entry function to do so.
70 static LogicalResult
71 getInterfaceVariables(spirv::FuncOp funcOp,
72                       SmallVectorImpl<Attribute> &interfaceVars) {
73   auto module = funcOp->getParentOfType<spirv::ModuleOp>();
74   if (!module) {
75     return failure();
76   }
77   SetVector<Operation *> interfaceVarSet;
78 
79   // TODO: This should in reality traverse the entry function
80   // call graph and collect all the interfaces. For now, just traverse the
81   // instructions in this function.
82   funcOp.walk([&](spirv::AddressOfOp addressOfOp) {
83     auto var =
84         module.lookupSymbol<spirv::GlobalVariableOp>(addressOfOp.variable());
85     // TODO: Per SPIR-V spec: "Before version 1.4, the interface’s
86     // storage classes are limited to the Input and Output storage classes.
87     // Starting with version 1.4, the interface’s storage classes are all
88     // storage classes used in declaring all global variables referenced by the
89     // entry point’s call tree." We should consider the target environment here.
90     switch (var.type().cast<spirv::PointerType>().getStorageClass()) {
91     case spirv::StorageClass::Input:
92     case spirv::StorageClass::Output:
93       interfaceVarSet.insert(var.getOperation());
94       break;
95     default:
96       break;
97     }
98   });
99   for (auto &var : interfaceVarSet) {
100     interfaceVars.push_back(SymbolRefAttr::get(
101         funcOp.getContext(), cast<spirv::GlobalVariableOp>(var).sym_name()));
102   }
103   return success();
104 }
105 
106 /// Lowers the entry point attribute.
107 static LogicalResult lowerEntryPointABIAttr(spirv::FuncOp funcOp,
108                                             OpBuilder &builder) {
109   auto entryPointAttrName = spirv::getEntryPointABIAttrName();
110   auto entryPointAttr =
111       funcOp->getAttrOfType<spirv::EntryPointABIAttr>(entryPointAttrName);
112   if (!entryPointAttr) {
113     return failure();
114   }
115 
116   OpBuilder::InsertionGuard moduleInsertionGuard(builder);
117   auto spirvModule = funcOp->getParentOfType<spirv::ModuleOp>();
118   builder.setInsertionPointToEnd(spirvModule.getBody());
119 
120   // Adds the spv.EntryPointOp after collecting all the interface variables
121   // needed.
122   SmallVector<Attribute, 1> interfaceVars;
123   if (failed(getInterfaceVariables(funcOp, interfaceVars))) {
124     return failure();
125   }
126 
127   spirv::TargetEnvAttr targetEnv = spirv::lookupTargetEnv(funcOp);
128   FailureOr<spirv::ExecutionModel> executionModel =
129       spirv::getExecutionModel(targetEnv);
130   if (failed(executionModel))
131     return funcOp.emitRemark("lower entry point failure: could not select "
132                              "execution model based on 'spv.target_env'");
133 
134   builder.create<spirv::EntryPointOp>(
135       funcOp.getLoc(), executionModel.getValue(), funcOp, interfaceVars);
136 
137   // Specifies the spv.ExecutionModeOp.
138   auto localSizeAttr = entryPointAttr.local_size();
139   SmallVector<int32_t, 3> localSize(localSizeAttr.getValues<int32_t>());
140   builder.create<spirv::ExecutionModeOp>(
141       funcOp.getLoc(), funcOp, spirv::ExecutionMode::LocalSize, localSize);
142   funcOp->removeAttr(entryPointAttrName);
143   return success();
144 }
145 
146 namespace {
147 /// A pattern to convert function signature according to interface variable ABI
148 /// attributes.
149 ///
150 /// Specifically, this pattern creates global variables according to interface
151 /// variable ABI attributes attached to function arguments and converts all
152 /// function argument uses to those global variables. This is necessary because
153 /// Vulkan requires all shader entry points to be of void(void) type.
154 class ProcessInterfaceVarABI final : public OpConversionPattern<spirv::FuncOp> {
155 public:
156   using OpConversionPattern<spirv::FuncOp>::OpConversionPattern;
157 
158   LogicalResult
159   matchAndRewrite(spirv::FuncOp funcOp, OpAdaptor adaptor,
160                   ConversionPatternRewriter &rewriter) const override;
161 };
162 
163 /// Pass to implement the ABI information specified as attributes.
164 class LowerABIAttributesPass final
165     : public SPIRVLowerABIAttributesBase<LowerABIAttributesPass> {
166   void runOnOperation() override;
167 };
168 } // namespace
169 
170 LogicalResult ProcessInterfaceVarABI::matchAndRewrite(
171     spirv::FuncOp funcOp, OpAdaptor adaptor,
172     ConversionPatternRewriter &rewriter) const {
173   if (!funcOp->getAttrOfType<spirv::EntryPointABIAttr>(
174           spirv::getEntryPointABIAttrName())) {
175     // TODO: Non-entry point functions are not handled.
176     return failure();
177   }
178   TypeConverter::SignatureConversion signatureConverter(
179       funcOp.getType().getNumInputs());
180 
181   auto &typeConverter = *getTypeConverter<SPIRVTypeConverter>();
182   auto indexType = typeConverter.getIndexType();
183 
184   auto attrName = spirv::getInterfaceVarABIAttrName();
185   for (auto argType : llvm::enumerate(funcOp.getType().getInputs())) {
186     auto abiInfo = funcOp.getArgAttrOfType<spirv::InterfaceVarABIAttr>(
187         argType.index(), attrName);
188     if (!abiInfo) {
189       // TODO: For non-entry point functions, it should be legal
190       // to pass around scalar/vector values and return a scalar/vector. For now
191       // non-entry point functions are not handled in this ABI lowering and will
192       // produce an error.
193       return failure();
194     }
195     spirv::GlobalVariableOp var = createGlobalVarForEntryPointArgument(
196         rewriter, funcOp, argType.index(), abiInfo);
197     if (!var)
198       return failure();
199 
200     OpBuilder::InsertionGuard funcInsertionGuard(rewriter);
201     rewriter.setInsertionPointToStart(&funcOp.front());
202     // Insert spirv::AddressOf and spirv::AccessChain operations.
203     Value replacement =
204         rewriter.create<spirv::AddressOfOp>(funcOp.getLoc(), var);
205     // Check if the arg is a scalar or vector type. In that case, the value
206     // needs to be loaded into registers.
207     // TODO: This is loading value of the scalar into registers
208     // at the start of the function. It is probably better to do the load just
209     // before the use. There might be multiple loads and currently there is no
210     // easy way to replace all uses with a sequence of operations.
211     if (argType.value().cast<spirv::SPIRVType>().isScalarOrVector()) {
212       auto zero =
213           spirv::ConstantOp::getZero(indexType, funcOp.getLoc(), rewriter);
214       auto loadPtr = rewriter.create<spirv::AccessChainOp>(
215           funcOp.getLoc(), replacement, zero.constant());
216       replacement = rewriter.create<spirv::LoadOp>(funcOp.getLoc(), loadPtr);
217     }
218     signatureConverter.remapInput(argType.index(), replacement);
219   }
220   if (failed(rewriter.convertRegionTypes(&funcOp.getBody(), *getTypeConverter(),
221                                          &signatureConverter)))
222     return failure();
223 
224   // Creates a new function with the update signature.
225   rewriter.updateRootInPlace(funcOp, [&] {
226     funcOp.setType(rewriter.getFunctionType(
227         signatureConverter.getConvertedTypes(), llvm::None));
228   });
229   return success();
230 }
231 
232 void LowerABIAttributesPass::runOnOperation() {
233   // Uses the signature conversion methodology of the dialect conversion
234   // framework to implement the conversion.
235   spirv::ModuleOp module = getOperation();
236   MLIRContext *context = &getContext();
237 
238   spirv::TargetEnv targetEnv(spirv::lookupTargetEnv(module));
239 
240   SPIRVTypeConverter typeConverter(targetEnv);
241 
242   // Insert a bitcast in the case of a pointer type change.
243   typeConverter.addSourceMaterialization([](OpBuilder &builder,
244                                             spirv::PointerType type,
245                                             ValueRange inputs, Location loc) {
246     if (inputs.size() != 1 || !inputs[0].getType().isa<spirv::PointerType>())
247       return Value();
248     return builder.create<spirv::BitcastOp>(loc, type, inputs[0]).getResult();
249   });
250 
251   RewritePatternSet patterns(context);
252   patterns.add<ProcessInterfaceVarABI>(typeConverter, context);
253 
254   ConversionTarget target(*context);
255   // "Legal" function ops should have no interface variable ABI attributes.
256   target.addDynamicallyLegalOp<spirv::FuncOp>([&](spirv::FuncOp op) {
257     StringRef attrName = spirv::getInterfaceVarABIAttrName();
258     for (unsigned i = 0, e = op.getNumArguments(); i < e; ++i)
259       if (op.getArgAttr(i, attrName))
260         return false;
261     return true;
262   });
263   // All other SPIR-V ops are legal.
264   target.markUnknownOpDynamicallyLegal([](Operation *op) {
265     return op->getDialect()->getNamespace() ==
266            spirv::SPIRVDialect::getDialectNamespace();
267   });
268   if (failed(applyPartialConversion(module, target, std::move(patterns))))
269     return signalPassFailure();
270 
271   // Walks over all the FuncOps in spirv::ModuleOp to lower the entry point
272   // attributes.
273   OpBuilder builder(context);
274   SmallVector<spirv::FuncOp, 1> entryPointFns;
275   auto entryPointAttrName = spirv::getEntryPointABIAttrName();
276   module.walk([&](spirv::FuncOp funcOp) {
277     if (funcOp->getAttrOfType<spirv::EntryPointABIAttr>(entryPointAttrName)) {
278       entryPointFns.push_back(funcOp);
279     }
280   });
281   for (auto fn : entryPointFns) {
282     if (failed(lowerEntryPointABIAttr(fn, builder))) {
283       return signalPassFailure();
284     }
285   }
286 }
287 
288 std::unique_ptr<OperationPass<spirv::ModuleOp>>
289 mlir::spirv::createLowerABIAttributesPass() {
290   return std::make_unique<LowerABIAttributesPass>();
291 }
292