1 //===- ControlFlowInterfaces.cpp - ControlFlow Interfaces -----------------===//
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 #include "mlir/Interfaces/ControlFlowInterfaces.h"
10 #include "mlir/IR/BuiltinTypes.h"
11 #include "llvm/ADT/SmallPtrSet.h"
12 
13 using namespace mlir;
14 
15 //===----------------------------------------------------------------------===//
16 // ControlFlowInterfaces
17 //===----------------------------------------------------------------------===//
18 
19 #include "mlir/Interfaces/ControlFlowInterfaces.cpp.inc"
20 
21 //===----------------------------------------------------------------------===//
22 // BranchOpInterface
23 //===----------------------------------------------------------------------===//
24 
25 /// Returns the `BlockArgument` corresponding to operand `operandIndex` in some
26 /// successor if 'operandIndex' is within the range of 'operands', or None if
27 /// `operandIndex` isn't a successor operand index.
28 Optional<BlockArgument>
29 detail::getBranchSuccessorArgument(Optional<OperandRange> operands,
30                                    unsigned operandIndex, Block *successor) {
31   // Check that the operands are valid.
32   if (!operands || operands->empty())
33     return llvm::None;
34 
35   // Check to ensure that this operand is within the range.
36   unsigned operandsStart = operands->getBeginOperandIndex();
37   if (operandIndex < operandsStart ||
38       operandIndex >= (operandsStart + operands->size()))
39     return llvm::None;
40 
41   // Index the successor.
42   unsigned argIndex = operandIndex - operandsStart;
43   return successor->getArgument(argIndex);
44 }
45 
46 /// Verify that the given operands match those of the given successor block.
47 LogicalResult
48 detail::verifyBranchSuccessorOperands(Operation *op, unsigned succNo,
49                                       Optional<OperandRange> operands) {
50   if (!operands)
51     return success();
52 
53   // Check the count.
54   unsigned operandCount = operands->size();
55   Block *destBB = op->getSuccessor(succNo);
56   if (operandCount != destBB->getNumArguments())
57     return op->emitError() << "branch has " << operandCount
58                            << " operands for successor #" << succNo
59                            << ", but target block has "
60                            << destBB->getNumArguments();
61 
62   // Check the types.
63   auto operandIt = operands->begin();
64   for (unsigned i = 0; i != operandCount; ++i, ++operandIt) {
65     if ((*operandIt).getType() != destBB->getArgument(i).getType())
66       return op->emitError() << "type mismatch for bb argument #" << i
67                              << " of successor #" << succNo;
68   }
69   return success();
70 }
71 
72 //===----------------------------------------------------------------------===//
73 // RegionBranchOpInterface
74 //===----------------------------------------------------------------------===//
75 
76 /// Verify that types match along all region control flow edges originating from
77 /// `sourceNo` (region # if source is a region, llvm::None if source is parent
78 /// op). `getInputsTypesForRegion` is a function that returns the types of the
79 /// inputs that flow from `sourceIndex' to the given region, or llvm::None if
80 /// the exact type match verification is not necessary (e.g., if the Op verifies
81 /// the match itself).
82 static LogicalResult
83 verifyTypesAlongAllEdges(Operation *op, Optional<unsigned> sourceNo,
84                          function_ref<Optional<TypeRange>(Optional<unsigned>)>
85                              getInputsTypesForRegion) {
86   auto regionInterface = cast<RegionBranchOpInterface>(op);
87 
88   SmallVector<RegionSuccessor, 2> successors;
89   unsigned numInputs;
90   if (sourceNo) {
91     Region &srcRegion = op->getRegion(sourceNo.getValue());
92     numInputs = srcRegion.getNumArguments();
93   } else {
94     numInputs = op->getNumOperands();
95   }
96   SmallVector<Attribute, 2> operands(numInputs, nullptr);
97   regionInterface.getSuccessorRegions(sourceNo, operands, successors);
98 
99   for (RegionSuccessor &succ : successors) {
100     Optional<unsigned> succRegionNo;
101     if (!succ.isParent())
102       succRegionNo = succ.getSuccessor()->getRegionNumber();
103 
104     auto printEdgeName = [&](InFlightDiagnostic &diag) -> InFlightDiagnostic & {
105       diag << "from ";
106       if (sourceNo)
107         diag << "Region #" << sourceNo.getValue();
108       else
109         diag << "parent operands";
110 
111       diag << " to ";
112       if (succRegionNo)
113         diag << "Region #" << succRegionNo.getValue();
114       else
115         diag << "parent results";
116       return diag;
117     };
118 
119     Optional<TypeRange> sourceTypes = getInputsTypesForRegion(succRegionNo);
120     if (!sourceTypes.hasValue())
121       continue;
122 
123     TypeRange succInputsTypes = succ.getSuccessorInputs().getTypes();
124     if (sourceTypes->size() != succInputsTypes.size()) {
125       InFlightDiagnostic diag = op->emitOpError(" region control flow edge ");
126       return printEdgeName(diag) << ": source has " << sourceTypes->size()
127                                  << " operands, but target successor needs "
128                                  << succInputsTypes.size();
129     }
130 
131     for (const auto &typesIdx :
132          llvm::enumerate(llvm::zip(*sourceTypes, succInputsTypes))) {
133       Type sourceType = std::get<0>(typesIdx.value());
134       Type inputType = std::get<1>(typesIdx.value());
135       if (sourceType != inputType) {
136         InFlightDiagnostic diag = op->emitOpError(" along control flow edge ");
137         return printEdgeName(diag)
138                << ": source type #" << typesIdx.index() << " " << sourceType
139                << " should match input type #" << typesIdx.index() << " "
140                << inputType;
141       }
142     }
143   }
144   return success();
145 }
146 
147 /// Verify that types match along control flow edges described the given op.
148 LogicalResult detail::verifyTypesAlongControlFlowEdges(Operation *op) {
149   auto regionInterface = cast<RegionBranchOpInterface>(op);
150 
151   auto inputTypesFromParent = [&](Optional<unsigned> regionNo) -> TypeRange {
152     if (regionNo.hasValue()) {
153       return regionInterface.getSuccessorEntryOperands(regionNo.getValue())
154           .getTypes();
155     }
156 
157     // If the successor of a parent op is the parent itself
158     // RegionBranchOpInterface does not have an API to query what the entry
159     // operands will be in that case. Vend out the result types of the op in
160     // that case so that type checking succeeds for this case.
161     return op->getResultTypes();
162   };
163 
164   // Verify types along control flow edges originating from the parent.
165   if (failed(verifyTypesAlongAllEdges(op, llvm::None, inputTypesFromParent)))
166     return failure();
167 
168   // RegionBranchOpInterface should not be implemented by Ops that do not have
169   // attached regions.
170   assert(op->getNumRegions() != 0);
171 
172   // Verify types along control flow edges originating from each region.
173   for (unsigned regionNo : llvm::seq(0U, op->getNumRegions())) {
174     Region &region = op->getRegion(regionNo);
175 
176     // Since there can be multiple `ReturnLike` terminators or others
177     // implementing the `RegionBranchTerminatorOpInterface`, all should have the
178     // same operand types when passing them to the same region.
179 
180     Optional<OperandRange> regionReturnOperands;
181     for (Block &block : region) {
182       Operation *terminator = block.getTerminator();
183       auto terminatorOperands =
184           getRegionBranchSuccessorOperands(terminator, regionNo);
185       if (!terminatorOperands)
186         continue;
187 
188       if (!regionReturnOperands) {
189         regionReturnOperands = terminatorOperands;
190         continue;
191       }
192 
193       // Found more than one ReturnLike terminator. Make sure the operand types
194       // match with the first one.
195       if (regionReturnOperands->getTypes() != terminatorOperands->getTypes())
196         return op->emitOpError("Region #")
197                << regionNo
198                << " operands mismatch between return-like terminators";
199     }
200 
201     auto inputTypesFromRegion =
202         [&](Optional<unsigned> regionNo) -> Optional<TypeRange> {
203       // If there is no return-like terminator, the op itself should verify
204       // type consistency.
205       if (!regionReturnOperands)
206         return llvm::None;
207 
208       // All successors get the same set of operand types.
209       return TypeRange(regionReturnOperands->getTypes());
210     };
211 
212     if (failed(verifyTypesAlongAllEdges(op, regionNo, inputTypesFromRegion)))
213       return failure();
214   }
215 
216   return success();
217 }
218 
219 /// Return `true` if `a` and `b` are in mutually exclusive regions.
220 ///
221 /// 1. Find the first common of `a` and `b` (ancestor) that implements
222 ///    RegionBranchOpInterface.
223 /// 2. Determine the regions `regionA` and `regionB` in which `a` and `b` are
224 ///    contained.
225 /// 3. Check if `regionA` and `regionB` are mutually exclusive. They are
226 ///    mutually exclusive if they are not reachable from each other as per
227 ///    RegionBranchOpInterface::getSuccessorRegions.
228 bool mlir::insideMutuallyExclusiveRegions(Operation *a, Operation *b) {
229   assert(a && "expected non-empty operation");
230   assert(b && "expected non-empty operation");
231 
232   auto branchOp = a->getParentOfType<RegionBranchOpInterface>();
233   while (branchOp) {
234     // Check if b is inside branchOp. (We already know that a is.)
235     if (!branchOp->isProperAncestor(b)) {
236       // Check next enclosing RegionBranchOpInterface.
237       branchOp = branchOp->getParentOfType<RegionBranchOpInterface>();
238       continue;
239     }
240 
241     // b is contained in branchOp. Retrieve the regions in which `a` and `b`
242     // are contained.
243     Region *regionA = nullptr, *regionB = nullptr;
244     for (Region &r : branchOp->getRegions()) {
245       if (r.findAncestorOpInRegion(*a)) {
246         assert(!regionA && "already found a region for a");
247         regionA = &r;
248       }
249       if (r.findAncestorOpInRegion(*b)) {
250         assert(!regionB && "already found a region for b");
251         regionB = &r;
252       }
253     }
254     assert(regionA && regionB && "could not find region of op");
255 
256     // Helper function that checks if region `r` is reachable from region
257     // `begin`.
258     std::function<bool(Region *, Region *)> isRegionReachable =
259         [&](Region *begin, Region *r) {
260           if (begin == r)
261             return true;
262           if (begin == nullptr)
263             return false;
264           // Compute index of region.
265           int64_t beginIndex = -1;
266           for (const auto &it : llvm::enumerate(branchOp->getRegions()))
267             if (&it.value() == begin)
268               beginIndex = it.index();
269           assert(beginIndex != -1 && "could not find region in op");
270           // Retrieve all successors of the region.
271           SmallVector<RegionSuccessor> successors;
272           branchOp.getSuccessorRegions(beginIndex, successors);
273           // Call function recursively on all successors.
274           for (RegionSuccessor successor : successors)
275             if (isRegionReachable(successor.getSuccessor(), r))
276               return true;
277           return false;
278         };
279 
280     // `a` and `b` are in mutually exclusive regions if neither region is
281     // reachable from the other region.
282     return !isRegionReachable(regionA, regionB) &&
283            !isRegionReachable(regionB, regionA);
284   }
285 
286   // Could not find a common RegionBranchOpInterface among a's and b's
287   // ancestors.
288   return false;
289 }
290 
291 //===----------------------------------------------------------------------===//
292 // RegionBranchTerminatorOpInterface
293 //===----------------------------------------------------------------------===//
294 
295 /// Returns true if the given operation is either annotated with the
296 /// `ReturnLike` trait or implements the `RegionBranchTerminatorOpInterface`.
297 bool mlir::isRegionReturnLike(Operation *operation) {
298   return dyn_cast<RegionBranchTerminatorOpInterface>(operation) ||
299          operation->hasTrait<OpTrait::ReturnLike>();
300 }
301 
302 /// Returns the mutable operands that are passed to the region with the given
303 /// `regionIndex`. If the operation does not implement the
304 /// `RegionBranchTerminatorOpInterface` and is not marked as `ReturnLike`, the
305 /// result will be `llvm::None`. In all other cases, the resulting
306 /// `OperandRange` represents all operands that are passed to the specified
307 /// successor region. If `regionIndex` is `llvm::None`, all operands that are
308 /// passed to the parent operation will be returned.
309 Optional<MutableOperandRange>
310 mlir::getMutableRegionBranchSuccessorOperands(Operation *operation,
311                                               Optional<unsigned> regionIndex) {
312   // Try to query a RegionBranchTerminatorOpInterface to determine
313   // all successor operands that will be passed to the successor
314   // input arguments.
315   if (auto regionTerminatorInterface =
316           dyn_cast<RegionBranchTerminatorOpInterface>(operation))
317     return regionTerminatorInterface.getMutableSuccessorOperands(regionIndex);
318 
319   // TODO: The ReturnLike trait should imply a default implementation of the
320   // RegionBranchTerminatorOpInterface. This would make this code significantly
321   // easier. Furthermore, this may even make this function obsolete.
322   if (operation->hasTrait<OpTrait::ReturnLike>())
323     return MutableOperandRange(operation);
324   return llvm::None;
325 }
326 
327 /// Returns the read only operands that are passed to the region with the given
328 /// `regionIndex`. See `getMutableRegionBranchSuccessorOperands` for more
329 /// information.
330 Optional<OperandRange>
331 mlir::getRegionBranchSuccessorOperands(Operation *operation,
332                                        Optional<unsigned> regionIndex) {
333   auto range = getMutableRegionBranchSuccessorOperands(operation, regionIndex);
334   return range ? Optional<OperandRange>(*range) : llvm::None;
335 }
336