[mlir][llvm] Add externally_initialized support to GlobalOp

This maps the `externally_initialized` flag in `llvm::GlobalVariable` to
`GlobalOp` and adds exported support.

Author: Mogball

mlir/include/mlir/Dialect/LLVMIR/LLVMOps.td

@@ -1122,6 +1122,7 @@ def LLVM_GlobalOp : LLVM_Op<"mlir.global",
     Linkage:$linkage,
     UnitAttr:$dso_local,
     UnitAttr:$thread_local_,
+    UnitAttr:$externally_initialized,
     OptionalAttr<AnyAttr>:$value,
     OptionalAttr<I64Attr>:$alignment,
     DefaultValuedAttr<ConfinedAttr<I32Attr, [IntNonNegative]>, "0">:$addr_space,

mlir/lib/Target/LLVMIR/ModuleTranslation.cpp

@@ -1021,7 +1021,6 @@ LogicalResult ModuleTranslation::convertGlobals() {
     }
 
     auto linkage = convertLinkageToLLVM(op.getLinkage());
-    auto addrSpace = op.getAddrSpace();
 
     // LLVM IR requires constant with linkage other than external or weak
     // external to have initializers. If MLIR does not provide an initializer,
@@ -1037,7 +1036,7 @@ LogicalResult ModuleTranslation::convertGlobals() {
         /*InsertBefore=*/nullptr,
         op.getThreadLocal_() ? llvm::GlobalValue::GeneralDynamicTLSModel
                              : llvm::GlobalValue::NotThreadLocal,
-        addrSpace);
+        op.getAddrSpace(), op.getExternallyInitialized());
 
     if (std::optional<mlir::SymbolRefAttr> comdat = op.getComdat()) {
       auto selectorOp = cast<ComdatSelectorOp>(

mlir/test/Target/LLVMIR/llvmir.mlir

@@ -39,6 +39,9 @@ llvm.mlir.global internal constant @string_const("foobar") : !llvm.array<6 x i8>
 // CHECK: @int_global_undef = internal global i64 undef
 llvm.mlir.global internal @int_global_undef() : i64
 
+// CHECK: @externally_initialized_global = internal externally_initialized global i32 0
+llvm.mlir.global internal @externally_initialized_global(0 : i32) {externally_initialized} : i32
+
 // CHECK: @f8E3M4_global_as_i8 = internal global i8 56
 llvm.mlir.global internal @f8E3M4_global_as_i8(1.5 : f8E3M4) : i8