1 //===- ModuleTranslation.cpp - MLIR to LLVM conversion --------------------===//
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 the translation between an MLIR LLVM dialect module and
10 // the corresponding LLVMIR module. It only handles core LLVM IR operations.
11 //
12 //===----------------------------------------------------------------------===//
13 
14 #include "mlir/Target/LLVMIR/ModuleTranslation.h"
15 
16 #include "DebugTranslation.h"
17 #include "mlir/Dialect/LLVMIR/LLVMDialect.h"
18 #include "mlir/Dialect/OpenMP/OpenMPDialect.h"
19 #include "mlir/IR/Attributes.h"
20 #include "mlir/IR/Module.h"
21 #include "mlir/IR/StandardTypes.h"
22 #include "mlir/Support/LLVM.h"
23 
24 #include "llvm/ADT/SetVector.h"
25 #include "llvm/Frontend/OpenMP/OMPIRBuilder.h"
26 #include "llvm/IR/BasicBlock.h"
27 #include "llvm/IR/Constants.h"
28 #include "llvm/IR/DerivedTypes.h"
29 #include "llvm/IR/IRBuilder.h"
30 #include "llvm/IR/LLVMContext.h"
31 #include "llvm/IR/Module.h"
32 #include "llvm/Transforms/Utils/Cloning.h"
33 
34 using namespace mlir;
35 using namespace mlir::LLVM;
36 using namespace mlir::LLVM::detail;
37 
38 #include "mlir/Dialect/LLVMIR/LLVMConversionEnumsToLLVM.inc"
39 
40 /// Builds a constant of a sequential LLVM type `type`, potentially containing
41 /// other sequential types recursively, from the individual constant values
42 /// provided in `constants`. `shape` contains the number of elements in nested
43 /// sequential types. Reports errors at `loc` and returns nullptr on error.
44 static llvm::Constant *
45 buildSequentialConstant(ArrayRef<llvm::Constant *> &constants,
46                         ArrayRef<int64_t> shape, llvm::Type *type,
47                         Location loc) {
48   if (shape.empty()) {
49     llvm::Constant *result = constants.front();
50     constants = constants.drop_front();
51     return result;
52   }
53 
54   if (!isa<llvm::SequentialType>(type)) {
55     emitError(loc) << "expected sequential LLVM types wrapping a scalar";
56     return nullptr;
57   }
58 
59   llvm::Type *elementType = type->getSequentialElementType();
60   SmallVector<llvm::Constant *, 8> nested;
61   nested.reserve(shape.front());
62   for (int64_t i = 0; i < shape.front(); ++i) {
63     nested.push_back(buildSequentialConstant(constants, shape.drop_front(),
64                                              elementType, loc));
65     if (!nested.back())
66       return nullptr;
67   }
68 
69   if (shape.size() == 1 && type->isVectorTy())
70     return llvm::ConstantVector::get(nested);
71   return llvm::ConstantArray::get(
72       llvm::ArrayType::get(elementType, shape.front()), nested);
73 }
74 
75 /// Returns the first non-sequential type nested in sequential types.
76 static llvm::Type *getInnermostElementType(llvm::Type *type) {
77   while (isa<llvm::SequentialType>(type))
78     type = type->getSequentialElementType();
79   return type;
80 }
81 
82 /// Create an LLVM IR constant of `llvmType` from the MLIR attribute `attr`.
83 /// This currently supports integer, floating point, splat and dense element
84 /// attributes and combinations thereof.  In case of error, report it to `loc`
85 /// and return nullptr.
86 llvm::Constant *ModuleTranslation::getLLVMConstant(llvm::Type *llvmType,
87                                                    Attribute attr,
88                                                    Location loc) {
89   if (!attr)
90     return llvm::UndefValue::get(llvmType);
91   if (llvmType->isStructTy()) {
92     emitError(loc, "struct types are not supported in constants");
93     return nullptr;
94   }
95   if (auto intAttr = attr.dyn_cast<IntegerAttr>())
96     return llvm::ConstantInt::get(llvmType, intAttr.getValue());
97   if (auto boolAttr = attr.dyn_cast<BoolAttr>())
98     return llvm::ConstantInt::get(llvmType, boolAttr.getValue());
99   if (auto floatAttr = attr.dyn_cast<FloatAttr>())
100     return llvm::ConstantFP::get(llvmType, floatAttr.getValue());
101   if (auto funcAttr = attr.dyn_cast<FlatSymbolRefAttr>())
102     return llvm::ConstantExpr::getBitCast(
103         functionMapping.lookup(funcAttr.getValue()), llvmType);
104   if (auto splatAttr = attr.dyn_cast<SplatElementsAttr>()) {
105     auto *sequentialType = cast<llvm::SequentialType>(llvmType);
106     auto elementType = sequentialType->getElementType();
107     uint64_t numElements = sequentialType->getNumElements();
108     // Splat value is a scalar. Extract it only if the element type is not
109     // another sequence type. The recursion terminates because each step removes
110     // one outer sequential type.
111     llvm::Constant *child = getLLVMConstant(
112         elementType,
113         isa<llvm::SequentialType>(elementType) ? splatAttr
114                                                : splatAttr.getSplatValue(),
115         loc);
116     if (!child)
117       return nullptr;
118     if (llvmType->isVectorTy())
119       return llvm::ConstantVector::getSplat(
120           llvm::ElementCount(numElements, /*Scalable=*/false), child);
121     if (llvmType->isArrayTy()) {
122       auto arrayType = llvm::ArrayType::get(elementType, numElements);
123       SmallVector<llvm::Constant *, 8> constants(numElements, child);
124       return llvm::ConstantArray::get(arrayType, constants);
125     }
126   }
127 
128   if (auto elementsAttr = attr.dyn_cast<ElementsAttr>()) {
129     assert(elementsAttr.getType().hasStaticShape());
130     assert(elementsAttr.getNumElements() != 0 &&
131            "unexpected empty elements attribute");
132     assert(!elementsAttr.getType().getShape().empty() &&
133            "unexpected empty elements attribute shape");
134 
135     SmallVector<llvm::Constant *, 8> constants;
136     constants.reserve(elementsAttr.getNumElements());
137     llvm::Type *innermostType = getInnermostElementType(llvmType);
138     for (auto n : elementsAttr.getValues<Attribute>()) {
139       constants.push_back(getLLVMConstant(innermostType, n, loc));
140       if (!constants.back())
141         return nullptr;
142     }
143     ArrayRef<llvm::Constant *> constantsRef = constants;
144     llvm::Constant *result = buildSequentialConstant(
145         constantsRef, elementsAttr.getType().getShape(), llvmType, loc);
146     assert(constantsRef.empty() && "did not consume all elemental constants");
147     return result;
148   }
149 
150   if (auto stringAttr = attr.dyn_cast<StringAttr>()) {
151     return llvm::ConstantDataArray::get(
152         llvmModule->getContext(), ArrayRef<char>{stringAttr.getValue().data(),
153                                                  stringAttr.getValue().size()});
154   }
155   emitError(loc, "unsupported constant value");
156   return nullptr;
157 }
158 
159 /// Convert MLIR integer comparison predicate to LLVM IR comparison predicate.
160 static llvm::CmpInst::Predicate getLLVMCmpPredicate(ICmpPredicate p) {
161   switch (p) {
162   case LLVM::ICmpPredicate::eq:
163     return llvm::CmpInst::Predicate::ICMP_EQ;
164   case LLVM::ICmpPredicate::ne:
165     return llvm::CmpInst::Predicate::ICMP_NE;
166   case LLVM::ICmpPredicate::slt:
167     return llvm::CmpInst::Predicate::ICMP_SLT;
168   case LLVM::ICmpPredicate::sle:
169     return llvm::CmpInst::Predicate::ICMP_SLE;
170   case LLVM::ICmpPredicate::sgt:
171     return llvm::CmpInst::Predicate::ICMP_SGT;
172   case LLVM::ICmpPredicate::sge:
173     return llvm::CmpInst::Predicate::ICMP_SGE;
174   case LLVM::ICmpPredicate::ult:
175     return llvm::CmpInst::Predicate::ICMP_ULT;
176   case LLVM::ICmpPredicate::ule:
177     return llvm::CmpInst::Predicate::ICMP_ULE;
178   case LLVM::ICmpPredicate::ugt:
179     return llvm::CmpInst::Predicate::ICMP_UGT;
180   case LLVM::ICmpPredicate::uge:
181     return llvm::CmpInst::Predicate::ICMP_UGE;
182   }
183   llvm_unreachable("incorrect comparison predicate");
184 }
185 
186 static llvm::CmpInst::Predicate getLLVMCmpPredicate(FCmpPredicate p) {
187   switch (p) {
188   case LLVM::FCmpPredicate::_false:
189     return llvm::CmpInst::Predicate::FCMP_FALSE;
190   case LLVM::FCmpPredicate::oeq:
191     return llvm::CmpInst::Predicate::FCMP_OEQ;
192   case LLVM::FCmpPredicate::ogt:
193     return llvm::CmpInst::Predicate::FCMP_OGT;
194   case LLVM::FCmpPredicate::oge:
195     return llvm::CmpInst::Predicate::FCMP_OGE;
196   case LLVM::FCmpPredicate::olt:
197     return llvm::CmpInst::Predicate::FCMP_OLT;
198   case LLVM::FCmpPredicate::ole:
199     return llvm::CmpInst::Predicate::FCMP_OLE;
200   case LLVM::FCmpPredicate::one:
201     return llvm::CmpInst::Predicate::FCMP_ONE;
202   case LLVM::FCmpPredicate::ord:
203     return llvm::CmpInst::Predicate::FCMP_ORD;
204   case LLVM::FCmpPredicate::ueq:
205     return llvm::CmpInst::Predicate::FCMP_UEQ;
206   case LLVM::FCmpPredicate::ugt:
207     return llvm::CmpInst::Predicate::FCMP_UGT;
208   case LLVM::FCmpPredicate::uge:
209     return llvm::CmpInst::Predicate::FCMP_UGE;
210   case LLVM::FCmpPredicate::ult:
211     return llvm::CmpInst::Predicate::FCMP_ULT;
212   case LLVM::FCmpPredicate::ule:
213     return llvm::CmpInst::Predicate::FCMP_ULE;
214   case LLVM::FCmpPredicate::une:
215     return llvm::CmpInst::Predicate::FCMP_UNE;
216   case LLVM::FCmpPredicate::uno:
217     return llvm::CmpInst::Predicate::FCMP_UNO;
218   case LLVM::FCmpPredicate::_true:
219     return llvm::CmpInst::Predicate::FCMP_TRUE;
220   }
221   llvm_unreachable("incorrect comparison predicate");
222 }
223 
224 static llvm::AtomicRMWInst::BinOp getLLVMAtomicBinOp(AtomicBinOp op) {
225   switch (op) {
226   case LLVM::AtomicBinOp::xchg:
227     return llvm::AtomicRMWInst::BinOp::Xchg;
228   case LLVM::AtomicBinOp::add:
229     return llvm::AtomicRMWInst::BinOp::Add;
230   case LLVM::AtomicBinOp::sub:
231     return llvm::AtomicRMWInst::BinOp::Sub;
232   case LLVM::AtomicBinOp::_and:
233     return llvm::AtomicRMWInst::BinOp::And;
234   case LLVM::AtomicBinOp::nand:
235     return llvm::AtomicRMWInst::BinOp::Nand;
236   case LLVM::AtomicBinOp::_or:
237     return llvm::AtomicRMWInst::BinOp::Or;
238   case LLVM::AtomicBinOp::_xor:
239     return llvm::AtomicRMWInst::BinOp::Xor;
240   case LLVM::AtomicBinOp::max:
241     return llvm::AtomicRMWInst::BinOp::Max;
242   case LLVM::AtomicBinOp::min:
243     return llvm::AtomicRMWInst::BinOp::Min;
244   case LLVM::AtomicBinOp::umax:
245     return llvm::AtomicRMWInst::BinOp::UMax;
246   case LLVM::AtomicBinOp::umin:
247     return llvm::AtomicRMWInst::BinOp::UMin;
248   case LLVM::AtomicBinOp::fadd:
249     return llvm::AtomicRMWInst::BinOp::FAdd;
250   case LLVM::AtomicBinOp::fsub:
251     return llvm::AtomicRMWInst::BinOp::FSub;
252   }
253   llvm_unreachable("incorrect atomic binary operator");
254 }
255 
256 static llvm::AtomicOrdering getLLVMAtomicOrdering(AtomicOrdering ordering) {
257   switch (ordering) {
258   case LLVM::AtomicOrdering::not_atomic:
259     return llvm::AtomicOrdering::NotAtomic;
260   case LLVM::AtomicOrdering::unordered:
261     return llvm::AtomicOrdering::Unordered;
262   case LLVM::AtomicOrdering::monotonic:
263     return llvm::AtomicOrdering::Monotonic;
264   case LLVM::AtomicOrdering::acquire:
265     return llvm::AtomicOrdering::Acquire;
266   case LLVM::AtomicOrdering::release:
267     return llvm::AtomicOrdering::Release;
268   case LLVM::AtomicOrdering::acq_rel:
269     return llvm::AtomicOrdering::AcquireRelease;
270   case LLVM::AtomicOrdering::seq_cst:
271     return llvm::AtomicOrdering::SequentiallyConsistent;
272   }
273   llvm_unreachable("incorrect atomic ordering");
274 }
275 
276 ModuleTranslation::ModuleTranslation(Operation *module,
277                                      std::unique_ptr<llvm::Module> llvmModule)
278     : mlirModule(module), llvmModule(std::move(llvmModule)),
279       debugTranslation(
280           std::make_unique<DebugTranslation>(module, *this->llvmModule)),
281       ompDialect(
282           module->getContext()->getRegisteredDialect<omp::OpenMPDialect>()) {
283   assert(satisfiesLLVMModule(mlirModule) &&
284          "mlirModule should honor LLVM's module semantics.");
285 }
286 ModuleTranslation::~ModuleTranslation() {}
287 
288 /// Given a single MLIR operation, create the corresponding LLVM IR operation
289 /// using the `builder`.  LLVM IR Builder does not have a generic interface so
290 /// this has to be a long chain of `if`s calling different functions with a
291 /// different number of arguments.
292 LogicalResult ModuleTranslation::convertOperation(Operation &opInst,
293                                                   llvm::IRBuilder<> &builder) {
294   auto extractPosition = [](ArrayAttr attr) {
295     SmallVector<unsigned, 4> position;
296     position.reserve(attr.size());
297     for (Attribute v : attr)
298       position.push_back(v.cast<IntegerAttr>().getValue().getZExtValue());
299     return position;
300   };
301 
302 #include "mlir/Dialect/LLVMIR/LLVMConversions.inc"
303 
304   // Emit function calls.  If the "callee" attribute is present, this is a
305   // direct function call and we also need to look up the remapped function
306   // itself.  Otherwise, this is an indirect call and the callee is the first
307   // operand, look it up as a normal value.  Return the llvm::Value representing
308   // the function result, which may be of llvm::VoidTy type.
309   auto convertCall = [this, &builder](Operation &op) -> llvm::Value * {
310     auto operands = lookupValues(op.getOperands());
311     ArrayRef<llvm::Value *> operandsRef(operands);
312     if (auto attr = op.getAttrOfType<FlatSymbolRefAttr>("callee")) {
313       return builder.CreateCall(functionMapping.lookup(attr.getValue()),
314                                 operandsRef);
315     } else {
316       return builder.CreateCall(operandsRef.front(), operandsRef.drop_front());
317     }
318   };
319 
320   // Emit calls.  If the called function has a result, remap the corresponding
321   // value.  Note that LLVM IR dialect CallOp has either 0 or 1 result.
322   if (isa<LLVM::CallOp>(opInst)) {
323     llvm::Value *result = convertCall(opInst);
324     if (opInst.getNumResults() != 0) {
325       valueMapping[opInst.getResult(0)] = result;
326       return success();
327     }
328     // Check that LLVM call returns void for 0-result functions.
329     return success(result->getType()->isVoidTy());
330   }
331 
332   if (auto invOp = dyn_cast<LLVM::InvokeOp>(opInst)) {
333     auto operands = lookupValues(opInst.getOperands());
334     ArrayRef<llvm::Value *> operandsRef(operands);
335     if (auto attr = opInst.getAttrOfType<FlatSymbolRefAttr>("callee"))
336       builder.CreateInvoke(functionMapping.lookup(attr.getValue()),
337                            blockMapping[invOp.getSuccessor(0)],
338                            blockMapping[invOp.getSuccessor(1)], operandsRef);
339     else
340       builder.CreateInvoke(
341           operandsRef.front(), blockMapping[invOp.getSuccessor(0)],
342           blockMapping[invOp.getSuccessor(1)], operandsRef.drop_front());
343     return success();
344   }
345 
346   if (auto lpOp = dyn_cast<LLVM::LandingpadOp>(opInst)) {
347     llvm::Type *ty = lpOp.getType().dyn_cast<LLVMType>().getUnderlyingType();
348     llvm::LandingPadInst *lpi =
349         builder.CreateLandingPad(ty, lpOp.getNumOperands());
350 
351     // Add clauses
352     for (auto operand : lookupValues(lpOp.getOperands())) {
353       // All operands should be constant - checked by verifier
354       if (auto constOperand = dyn_cast<llvm::Constant>(operand))
355         lpi->addClause(constOperand);
356     }
357     valueMapping[lpOp.getResult()] = lpi;
358     return success();
359   }
360 
361   // Emit branches.  We need to look up the remapped blocks and ignore the block
362   // arguments that were transformed into PHI nodes.
363   if (auto brOp = dyn_cast<LLVM::BrOp>(opInst)) {
364     builder.CreateBr(blockMapping[brOp.getSuccessor()]);
365     return success();
366   }
367   if (auto condbrOp = dyn_cast<LLVM::CondBrOp>(opInst)) {
368     builder.CreateCondBr(valueMapping.lookup(condbrOp.getOperand(0)),
369                          blockMapping[condbrOp.getSuccessor(0)],
370                          blockMapping[condbrOp.getSuccessor(1)]);
371     return success();
372   }
373 
374   // Emit addressof.  We need to look up the global value referenced by the
375   // operation and store it in the MLIR-to-LLVM value mapping.  This does not
376   // emit any LLVM instruction.
377   if (auto addressOfOp = dyn_cast<LLVM::AddressOfOp>(opInst)) {
378     LLVM::GlobalOp global = addressOfOp.getGlobal();
379     // The verifier should not have allowed this.
380     assert(global && "referencing an undefined global");
381 
382     valueMapping[addressOfOp.getResult()] = globalsMapping.lookup(global);
383     return success();
384   }
385 
386   if (opInst.getDialect() == ompDialect) {
387     if (!ompBuilder) {
388       ompBuilder = std::make_unique<llvm::OpenMPIRBuilder>(*llvmModule);
389       ompBuilder->initialize();
390     }
391 
392     if (isa<omp::BarrierOp>(opInst)) {
393       ompBuilder->CreateBarrier(builder.saveIP(), llvm::omp::OMPD_barrier);
394       return success();
395     }
396     return opInst.emitError("unsupported OpenMP operation: ")
397            << opInst.getName();
398   }
399 
400   return opInst.emitError("unsupported or non-LLVM operation: ")
401          << opInst.getName();
402 }
403 
404 /// Convert block to LLVM IR.  Unless `ignoreArguments` is set, emit PHI nodes
405 /// to define values corresponding to the MLIR block arguments.  These nodes
406 /// are not connected to the source basic blocks, which may not exist yet.
407 LogicalResult ModuleTranslation::convertBlock(Block &bb, bool ignoreArguments) {
408   llvm::IRBuilder<> builder(blockMapping[&bb]);
409   auto *subprogram = builder.GetInsertBlock()->getParent()->getSubprogram();
410 
411   // Before traversing operations, make block arguments available through
412   // value remapping and PHI nodes, but do not add incoming edges for the PHI
413   // nodes just yet: those values may be defined by this or following blocks.
414   // This step is omitted if "ignoreArguments" is set.  The arguments of the
415   // first block have been already made available through the remapping of
416   // LLVM function arguments.
417   if (!ignoreArguments) {
418     auto predecessors = bb.getPredecessors();
419     unsigned numPredecessors =
420         std::distance(predecessors.begin(), predecessors.end());
421     for (auto arg : bb.getArguments()) {
422       auto wrappedType = arg.getType().dyn_cast<LLVM::LLVMType>();
423       if (!wrappedType)
424         return emitError(bb.front().getLoc(),
425                          "block argument does not have an LLVM type");
426       llvm::Type *type = wrappedType.getUnderlyingType();
427       llvm::PHINode *phi = builder.CreatePHI(type, numPredecessors);
428       valueMapping[arg] = phi;
429     }
430   }
431 
432   // Traverse operations.
433   for (auto &op : bb) {
434     // Set the current debug location within the builder.
435     builder.SetCurrentDebugLocation(
436         debugTranslation->translateLoc(op.getLoc(), subprogram));
437 
438     if (failed(convertOperation(op, builder)))
439       return failure();
440   }
441 
442   return success();
443 }
444 
445 /// Create named global variables that correspond to llvm.mlir.global
446 /// definitions.
447 LogicalResult ModuleTranslation::convertGlobals() {
448   for (auto op : getModuleBody(mlirModule).getOps<LLVM::GlobalOp>()) {
449     llvm::Type *type = op.getType().getUnderlyingType();
450     llvm::Constant *cst = llvm::UndefValue::get(type);
451     if (op.getValueOrNull()) {
452       // String attributes are treated separately because they cannot appear as
453       // in-function constants and are thus not supported by getLLVMConstant.
454       if (auto strAttr = op.getValueOrNull().dyn_cast_or_null<StringAttr>()) {
455         cst = llvm::ConstantDataArray::getString(
456             llvmModule->getContext(), strAttr.getValue(), /*AddNull=*/false);
457         type = cst->getType();
458       } else if (!(cst = getLLVMConstant(type, op.getValueOrNull(),
459                                          op.getLoc()))) {
460         return failure();
461       }
462     } else if (Block *initializer = op.getInitializerBlock()) {
463       llvm::IRBuilder<> builder(llvmModule->getContext());
464       for (auto &op : initializer->without_terminator()) {
465         if (failed(convertOperation(op, builder)) ||
466             !isa<llvm::Constant>(valueMapping.lookup(op.getResult(0))))
467           return emitError(op.getLoc(), "unemittable constant value");
468       }
469       ReturnOp ret = cast<ReturnOp>(initializer->getTerminator());
470       cst = cast<llvm::Constant>(valueMapping.lookup(ret.getOperand(0)));
471     }
472 
473     auto linkage = convertLinkageToLLVM(op.linkage());
474     bool anyExternalLinkage =
475         ((linkage == llvm::GlobalVariable::ExternalLinkage &&
476           isa<llvm::UndefValue>(cst)) ||
477          linkage == llvm::GlobalVariable::ExternalWeakLinkage);
478     auto addrSpace = op.addr_space().getLimitedValue();
479     auto *var = new llvm::GlobalVariable(
480         *llvmModule, type, op.constant(), linkage,
481         anyExternalLinkage ? nullptr : cst, op.sym_name(),
482         /*InsertBefore=*/nullptr, llvm::GlobalValue::NotThreadLocal, addrSpace);
483 
484     globalsMapping.try_emplace(op, var);
485   }
486 
487   return success();
488 }
489 
490 /// Get the SSA value passed to the current block from the terminator operation
491 /// of its predecessor.
492 static Value getPHISourceValue(Block *current, Block *pred,
493                                unsigned numArguments, unsigned index) {
494   auto &terminator = *pred->getTerminator();
495   if (isa<LLVM::BrOp>(terminator)) {
496     return terminator.getOperand(index);
497   }
498 
499   // For conditional branches, we need to check if the current block is reached
500   // through the "true" or the "false" branch and take the relevant operands.
501   auto condBranchOp = dyn_cast<LLVM::CondBrOp>(terminator);
502   assert(condBranchOp &&
503          "only branch operations can be terminators of a block that "
504          "has successors");
505   assert((condBranchOp.getSuccessor(0) != condBranchOp.getSuccessor(1)) &&
506          "successors with arguments in LLVM conditional branches must be "
507          "different blocks");
508 
509   return condBranchOp.getSuccessor(0) == current
510              ? condBranchOp.trueDestOperands()[index]
511              : condBranchOp.falseDestOperands()[index];
512 }
513 
514 void ModuleTranslation::connectPHINodes(LLVMFuncOp func) {
515   // Skip the first block, it cannot be branched to and its arguments correspond
516   // to the arguments of the LLVM function.
517   for (auto it = std::next(func.begin()), eit = func.end(); it != eit; ++it) {
518     Block *bb = &*it;
519     llvm::BasicBlock *llvmBB = blockMapping.lookup(bb);
520     auto phis = llvmBB->phis();
521     auto numArguments = bb->getNumArguments();
522     assert(numArguments == std::distance(phis.begin(), phis.end()));
523     for (auto &numberedPhiNode : llvm::enumerate(phis)) {
524       auto &phiNode = numberedPhiNode.value();
525       unsigned index = numberedPhiNode.index();
526       for (auto *pred : bb->getPredecessors()) {
527         phiNode.addIncoming(valueMapping.lookup(getPHISourceValue(
528                                 bb, pred, numArguments, index)),
529                             blockMapping.lookup(pred));
530       }
531     }
532   }
533 }
534 
535 // TODO(mlir-team): implement an iterative version
536 static void topologicalSortImpl(llvm::SetVector<Block *> &blocks, Block *b) {
537   blocks.insert(b);
538   for (Block *bb : b->getSuccessors()) {
539     if (blocks.count(bb) == 0)
540       topologicalSortImpl(blocks, bb);
541   }
542 }
543 
544 /// Sort function blocks topologically.
545 static llvm::SetVector<Block *> topologicalSort(LLVMFuncOp f) {
546   // For each blocks that has not been visited yet (i.e. that has no
547   // predecessors), add it to the list and traverse its successors in DFS
548   // preorder.
549   llvm::SetVector<Block *> blocks;
550   for (Block &b : f.getBlocks()) {
551     if (blocks.count(&b) == 0)
552       topologicalSortImpl(blocks, &b);
553   }
554   assert(blocks.size() == f.getBlocks().size() && "some blocks are not sorted");
555 
556   return blocks;
557 }
558 
559 LogicalResult ModuleTranslation::convertOneFunction(LLVMFuncOp func) {
560   // Clear the block and value mappings, they are only relevant within one
561   // function.
562   blockMapping.clear();
563   valueMapping.clear();
564   llvm::Function *llvmFunc = functionMapping.lookup(func.getName());
565 
566   // Translate the debug information for this function.
567   debugTranslation->translate(func, *llvmFunc);
568 
569   // Add function arguments to the value remapping table.
570   // If there was noalias info then we decorate each argument accordingly.
571   unsigned int argIdx = 0;
572   for (auto kvp : llvm::zip(func.getArguments(), llvmFunc->args())) {
573     llvm::Argument &llvmArg = std::get<1>(kvp);
574     BlockArgument mlirArg = std::get<0>(kvp);
575 
576     if (auto attr = func.getArgAttrOfType<BoolAttr>(argIdx, "llvm.noalias")) {
577       // NB: Attribute already verified to be boolean, so check if we can indeed
578       // attach the attribute to this argument, based on its type.
579       auto argTy = mlirArg.getType().dyn_cast<LLVM::LLVMType>();
580       if (!argTy.getUnderlyingType()->isPointerTy())
581         return func.emitError(
582             "llvm.noalias attribute attached to LLVM non-pointer argument");
583       if (attr.getValue())
584         llvmArg.addAttr(llvm::Attribute::AttrKind::NoAlias);
585     }
586     valueMapping[mlirArg] = &llvmArg;
587     argIdx++;
588   }
589 
590   // Check the personality and set it.
591   if (func.personality().hasValue()) {
592     llvm::Type *ty = llvm::Type::getInt8PtrTy(llvmFunc->getContext());
593     if (llvm::Constant *pfunc =
594             getLLVMConstant(ty, func.personalityAttr(), func.getLoc()))
595       llvmFunc->setPersonalityFn(pfunc);
596   }
597 
598   // First, create all blocks so we can jump to them.
599   llvm::LLVMContext &llvmContext = llvmFunc->getContext();
600   for (auto &bb : func) {
601     auto *llvmBB = llvm::BasicBlock::Create(llvmContext);
602     llvmBB->insertInto(llvmFunc);
603     blockMapping[&bb] = llvmBB;
604   }
605 
606   // Then, convert blocks one by one in topological order to ensure defs are
607   // converted before uses.
608   auto blocks = topologicalSort(func);
609   for (auto indexedBB : llvm::enumerate(blocks)) {
610     auto *bb = indexedBB.value();
611     if (failed(convertBlock(*bb, /*ignoreArguments=*/indexedBB.index() == 0)))
612       return failure();
613   }
614 
615   // Finally, after all blocks have been traversed and values mapped, connect
616   // the PHI nodes to the results of preceding blocks.
617   connectPHINodes(func);
618   return success();
619 }
620 
621 LogicalResult ModuleTranslation::checkSupportedModuleOps(Operation *m) {
622   for (Operation &o : getModuleBody(m).getOperations())
623     if (!isa<LLVM::LLVMFuncOp>(&o) && !isa<LLVM::GlobalOp>(&o) &&
624         !o.isKnownTerminator())
625       return o.emitOpError("unsupported module-level operation");
626   return success();
627 }
628 
629 LogicalResult ModuleTranslation::convertFunctions() {
630   // Declare all functions first because there may be function calls that form a
631   // call graph with cycles.
632   for (auto function : getModuleBody(mlirModule).getOps<LLVMFuncOp>()) {
633     llvm::FunctionCallee llvmFuncCst = llvmModule->getOrInsertFunction(
634         function.getName(),
635         cast<llvm::FunctionType>(function.getType().getUnderlyingType()));
636     assert(isa<llvm::Function>(llvmFuncCst.getCallee()));
637     functionMapping[function.getName()] =
638         cast<llvm::Function>(llvmFuncCst.getCallee());
639   }
640 
641   // Convert functions.
642   for (auto function : getModuleBody(mlirModule).getOps<LLVMFuncOp>()) {
643     // Ignore external functions.
644     if (function.isExternal())
645       continue;
646 
647     if (failed(convertOneFunction(function)))
648       return failure();
649   }
650 
651   return success();
652 }
653 
654 /// A helper to look up remapped operands in the value remapping table.`
655 SmallVector<llvm::Value *, 8>
656 ModuleTranslation::lookupValues(ValueRange values) {
657   SmallVector<llvm::Value *, 8> remapped;
658   remapped.reserve(values.size());
659   for (Value v : values) {
660     assert(valueMapping.count(v) && "referencing undefined value");
661     remapped.push_back(valueMapping.lookup(v));
662   }
663   return remapped;
664 }
665 
666 std::unique_ptr<llvm::Module>
667 ModuleTranslation::prepareLLVMModule(Operation *m) {
668   auto *dialect = m->getContext()->getRegisteredDialect<LLVM::LLVMDialect>();
669   assert(dialect && "LLVM dialect must be registered");
670 
671   auto llvmModule = llvm::CloneModule(dialect->getLLVMModule());
672   if (!llvmModule)
673     return nullptr;
674 
675   llvm::LLVMContext &llvmContext = llvmModule->getContext();
676   llvm::IRBuilder<> builder(llvmContext);
677 
678   // Inject declarations for `malloc` and `free` functions that can be used in
679   // memref allocation/deallocation coming from standard ops lowering.
680   llvmModule->getOrInsertFunction("malloc", builder.getInt8PtrTy(),
681                                   builder.getInt64Ty());
682   llvmModule->getOrInsertFunction("free", builder.getVoidTy(),
683                                   builder.getInt8PtrTy());
684 
685   return llvmModule;
686 }
687