[mlir][llvm] Support importing magic globals

[Dinistro]

Summary

This commit adds support for importing the magic globals "global_ctors"
and "global_dtors" from LLVM IR to the LLVM IR dialect. The import
fails when these globals have a non-null data pointer, as this can
currently not be represented in the corresponding MLIR operations.

[gysit]

mlir/include/mlir/Target/LLVMIR/ModuleImport.h

61

I would probably rename to convertGlobalCtorsAndDtors since most modern functions use convert instead of process. Also let's make it a private method except there is a good reason to not do that.

mlir/lib/Target/LLVMIR/ModuleImport.cpp

324

nit: drop newline

326–327

nit: Let's use braces for multi-line if statements.

577

nit: prio -> priority? and maybe init -> initializer?

596

After creating the GlobalCtorsOp/GlobalDtorsOp also update the globalInsertionOp (cf. line 540 in process global).

598

nit: As this is used twice I would suggest to add a getGlobalCtorVarName() or similar?

604

nit: Let's use mlirModule->getLoc() instead of UnknownLoc since we actually know at least the filename. I plan to change this for the other globals as well (the change has been discussed/suggested in https://reviews.llvm.org/D140768.

mlir/test/Target/LLVMIR/Import/import-failure.ll

41

nit: drop the newline here and below and also add "error" on the check line to make sure the code emits an error. I would probably also match at least the start of the variable.

72

nit: can you comment for the different tests why the import is supposed to fail?

[Dinistro]

address review comments

[Dinistro]

mlir/lib/Target/LLVMIR/ModuleImport.cpp

598

Added a constexpr on the top instead.

[Dinistro]

additional minor fixes

[gysit]

LGTM!

[Dinistro]

Fix error location to point to module loc

mlir/include/mlir/Target/LLVMIR/ModuleImport.h

public:
   LogicalResult initializeImportInterface() { return iface.initializeImport(); }
 
   /// Converts all functions of the LLVM module to MLIR functions.
   LogicalResult convertFunctions();
 
   /// Converts all global variables of the LLVM module to MLIR global variables.
   LogicalResult convertGlobals();
 
+  /// Imports the magic globals "global_ctors" and "global_dtors".
+  LogicalResult processGlobalCtorsAndDtors(llvm::GlobalVariable *globalVar);
+
   /// Stores the mapping between an LLVM value and its MLIR counterpart.
   void mapValue(llvm::Value *llvm, Value mlir) { mapValue(llvm) = mlir; }
 
   /// Provides write-once access to store the MLIR value corresponding to the
   /// given LLVM value.
   Value &mapValue(llvm::Value *value) {
     Value &mlir = valueMapping[value];
     assert(mlir == nullptr &&

mlir/lib/Target/LLVMIR/ModuleImport.cpp

: builder(mlirModule->getContext()), context(mlirModule->getContext()),
       mlirModule(mlirModule), llvmModule(std::move(llvmModule)),
       iface(mlirModule->getContext()),
       typeTranslator(*mlirModule->getContext()),
       debugImporter(std::make_unique<DebugImporter>(mlirModule->getContext())) {
   builder.setInsertionPointToStart(mlirModule.getBody());
 }
 
 LogicalResult ModuleImport::convertGlobals() {
-  for (llvm::GlobalVariable &globalVar : llvmModule->globals())
+  for (llvm::GlobalVariable &globalVar : llvmModule->globals()) {
+    if (globalVar.getName() == "llvm.global_ctors" ||
+        globalVar.getName() == "llvm.global_dtors") {
+
+      if (failed(processGlobalCtorsAndDtors(&globalVar)))
+        return emitError(UnknownLoc::get(context))
+               << "unhandled global variable" << diag(globalVar);
+
+      continue;
+    }
+
     if (!processGlobal(&globalVar))
       return failure();
+  }
   return success();
 }
 
 LogicalResult ModuleImport::convertFunctions() {
   for (llvm::Function &func : llvmModule->functions())
     if (failed(processFunction(&func)))
       return failure();
   return success();
globalOp.setUnnamedAddr(
         convertUnnamedAddrFromLLVM(globalVar->getUnnamedAddr()));
   }
   if (globalVar->hasSection())
     globalOp.setSection(globalVar->getSection());
 
   return globals[globalVar] = globalOp;
 }
 
+LogicalResult
+ModuleImport::processGlobalCtorsAndDtors(llvm::GlobalVariable *globalVar) {
+  if (!globalVar->hasInitializer() || !globalVar->hasAppendingLinkage())
+    return failure();
+  auto *init = dyn_cast<llvm::ConstantArray>(globalVar->getInitializer());
+  if (!init)
+    return failure();
+
+  SmallVector<Attribute> funcs;
+  SmallVector<int32_t> prios;
+  for (llvm::Value *operand : init->operands()) {
+    auto *aggregate = dyn_cast<llvm::ConstantAggregate>(operand);
+    if (!aggregate || aggregate->getNumOperands() != 3)
+      return failure();
+
+    auto *prio = dyn_cast<llvm::ConstantInt>(aggregate->getOperand(0));
+    auto *func = dyn_cast<llvm::Function>(aggregate->getOperand(1));
+    auto *data = dyn_cast<llvm::Constant>(aggregate->getOperand(2));
+    if (!prio || !func || !data)
+      return failure();
+
+    // global_ctros and global_dtors with non-null data field are not supported
+    // in MLIR.
+    if (!data->isNullValue())
+      return failure();
+
+    funcs.push_back(FlatSymbolRefAttr::get(context, func->getName()));
+    prios.push_back(prio->getValue().getZExtValue());
+  }
+
+  OpBuilder::InsertionGuard guard(builder);
+  if (!globalInsertionOp)
+    builder.setInsertionPointToStart(mlirModule.getBody());
+  else
+    builder.setInsertionPointAfter(globalInsertionOp);
+
+  if (globalVar->getName() == "llvm.global_ctors") {
+    builder.create<LLVM::GlobalCtorsOp>(UnknownLoc::get(context),
+                                        builder.getArrayAttr(funcs),
+                                        builder.getI32ArrayAttr(prios));
+    return success();
+  }
+  builder.create<LLVM::GlobalDtorsOp>(UnknownLoc::get(context),
+                                      builder.getArrayAttr(funcs),
+                                      builder.getI32ArrayAttr(prios));
+  return success();
+}
+
 SetVector<llvm::Constant *>
 ModuleImport::getConstantsToConvert(llvm::Constant *constant) {
   // Traverse the constant dependencies in post order.
   SmallVector<llvm::Constant *> workList;
   SmallVector<llvm::Constant *> orderedList;
   workList.push_back(constant);
   while (!workList.empty()) {
     llvm::Constant *current = workList.pop_back_val();

mlir/test/Target/LLVMIR/Import/global-variables.ll

 ; CHECK-SAME:  (dense<[{{\[}}[1, 2], [3, 4]]]> : tensor<1x2x2xi32>)
 ; CHECK-SAME:  {addr_space = 0 : i32, dso_local} : !llvm.array<1 x array<2 x array<2 x i32>>>
 @nested_array_constant3 = internal constant [1 x [2 x [2 x i32]]] [[2 x [2 x i32]] [[2 x i32] [i32 1, i32 2], [2 x i32] [i32 3, i32 4]]]
 
 ; CHECK: llvm.mlir.global internal constant @nested_array_vector
 ; CHECK-SAME:  (dense<[{{\[}}[1, 2], [3, 4]]]> : vector<1x2x2xi32>)
 ; CHECK-SAME:   {addr_space = 0 : i32, dso_local} : !llvm.array<1 x array<2 x vector<2xi32>>>
 @nested_array_vector = internal constant [1 x [2 x <2 x i32>]] [[2 x <2 x i32>] [<2 x i32> <i32 1, i32 2>, <2 x i32> <i32 3, i32 4>]]
+
+; // -----
+
+; CHECK-DAG: llvm.mlir.global_ctors {ctors = [@foo, @bar], priorities = [0 : i32, 42 : i32]}
+; CHECK-DAG: llvm.mlir.global_dtors {dtors = [@foo], priorities = [0 : i32]}
[e-mail]_ctors = appending global [2 x { i32, ptr, ptr }] [{ i32, ptr, ptr } { i32 0, ptr @foo, ptr null }, { i32, ptr, ptr } { i32 42, ptr @bar, ptr null }]
[e-mail]_dtors = appending global [1 x { i32, ptr, ptr }] [{ i32, ptr, ptr } { i32 0, ptr @foo, ptr null }]
+
+define void @foo() {
+  ret void
+}
+
+define void @bar() {
+  ret void
+}

mlir/test/Target/LLVMIR/Import/import-failure.ll

 
 declare void @llvm.gcroot(ptr %arg0, ptr %arg1)
 
 ; CHECK: unhandled intrinsic call void @llvm.gcroot(ptr %arg0, ptr %arg1)
 define void @unhandled_intrinsic(ptr %arg0, ptr %arg1) {
   call void @llvm.gcroot(ptr %arg0, ptr %arg1)
   ret void
 }
+
+; // -----
+
+; CHECK: unhandled global variable
+
[e-mail]_ctors = global [1 x { i32, ptr, ptr }] [{ i32, ptr, ptr } { i32 0, ptr @foo, ptr null }]
+
+define void @foo() {
+  ret void
+}
+
+; // -----
+
+; CHECK: unhandled global variable
+
[e-mail]_ctors = appending global [1 x { i32, ptr }] [{ i32, ptr } { i32 0, ptr @foo }]
+
+define void @foo() {
+  ret void
+}
+
+; // -----
+
+; CHECK: unhandled global variable
+
[e-mail]_ctors = appending global [1 x { i32, ptr, ptr }] [{ i32, ptr, ptr } { i32 0, ptr @foo, ptr @foo }]
+
+define void @foo() {
+  ret void
+}
+
+; // -----
+
+; CHECK: unhandled global variable
+
[e-mail]_ctors = appending global [1 x { ptr, i32, ptr }] [{ ptr, i32, ptr } { ptr @foo, i32 0, ptr null }]
+
+define void @foo() {
+  ret void
+}