[MLIR][mlir-link] Don't crash when structor list to link is empty

Author: frabert

mlir/include/mlir/Dialect/LLVMIR/LLVMLinkerInterface.h

@@ -39,8 +39,8 @@ class LLVMSymbolLinkerInterface
       if (auto found = append.find("llvm.global_ctors"); found != append.end())
         toLink = append.find("llvm.global_ctors")->second;
     } else if constexpr (std::is_same<LLVM::GlobalDtorsOp, structor_t>()) {
-      if (auto found = append.find("llvm.global_ctors"); found != append.end())
-        toLink = append.find("llvm.global_ctors")->second;
+      if (auto found = append.find("llvm.global_dtors"); found != append.end())
+        toLink = append.find("llvm.global_dtors")->second;
     }
 
     std::vector<Attribute> newStructorList;
@@ -82,12 +82,19 @@ class LLVMSymbolLinkerInterface
       }
     }
 
-    auto cloned = state.clone(toLink.back());
+    auto ctx = state.getDestinationOp()->getContext();
     auto newStructorsAttr =
-        mlir::ArrayAttr::get(cloned->getContext(), newStructorList);
+        mlir::ArrayAttr::get(ctx, newStructorList);
     auto newPrioritiesAttr =
-        mlir::ArrayAttr::get(cloned->getContext(), newPriorities);
-    auto newDataAttr = mlir::ArrayAttr::get(cloned->getContext(), newData);
+        mlir::ArrayAttr::get(ctx, newPriorities);
+    auto newDataAttr = mlir::ArrayAttr::get(ctx, newData);
+
+    Operation *cloned;
+    if (toLink.empty()) {
+      cloned = state.create<structor_t>(UnknownLoc::get(ctx), newStructorsAttr, newPrioritiesAttr, newDataAttr);
+    } else {
+      cloned = state.clone(toLink.back());
+    }
 
     if constexpr (std::is_same<LLVM::GlobalCtorsOp, structor_t>()) {
       auto ctor = cast<LLVM::GlobalCtorsOp>(cloned);

mlir/include/mlir/Linker/LinkerInterface.h

@@ -55,6 +55,11 @@ class LinkState {
   }
   SymbolUserMap &getSymbolUserMap(ModuleOp mod);
 
+  template<typename Op, typename... Args>
+  auto create(Location location, Args&&... args) {
+    return builder.create<Op>(location, std::forward<Args>(args)...);
+  }
+
 private:
   // Private constructor used by nest()
   LinkState(ModuleOp dst, std::shared_ptr<IRMapping> mapping)

mlir/test/mlir-link/global-structors-b.mlir

@@ -0,0 +1,20 @@
+// RUN: mlir-link -sort-symbols -split-input-file %s | FileCheck %s
+
+// CHECK: llvm.func internal @foo
+// CHECK: llvm.mlir.global_ctors ctors = [@foo]
+
+llvm.comdat @__llvm_global_comdat {
+    llvm.comdat_selector @foo any
+}
+
+llvm.mlir.global_ctors ctors = [@foo], priorities = [65535 : i32], data = [#llvm.zero]
+llvm.func internal @foo() -> i32 {
+  %0 = llvm.mlir.constant(0 : i32) : i32
+  llvm.return %0 : i32
+}
+
+// -----
+
+llvm.comdat @__llvm_global_comdat {
+    llvm.comdat_selector @bar any
+}