[Flang][MLIR] Alter Fir.GlobalOp to print and lower external attributes

Fir.GlobalOp's currently do not respect attributes that
are applied to them, this change will do two things:

- Allow lowering of arbitrary attributes applied to
Fir.GlobalOp's to LLVMGlobalOp's during CodeGen
- Allow printing and parsing of arbitrarily applied attributes

This allows applying other dialects attributes (or other
fir attributes) to fir.GlobalOps on the fly and have them
exist in the resulting LLVM dialect IR or FIR IR.

Reviewer: jeanPerier

Differential Revision: https://reviews.llvm.org/D148352

flang/lib/Optimizer/CodeGen/CodeGen.cpp

@@ -2855,6 +2855,16 @@ struct GlobalOpConversion : public FIROpConversion<fir::GlobalOp> {
     auto isConst = global.getConstant().has_value();
     auto g = rewriter.create<mlir::LLVM::GlobalOp>(
         loc, tyAttr, isConst, linkage, global.getSymName(), initAttr);
+
+    // Apply all non-Fir::GlobalOp attributes to the LLVM::GlobalOp, preserving
+    // them; whilst taking care not to apply attributes that are lowered in
+    // other ways.
+    llvm::SmallDenseSet<llvm::StringRef> elidedAttrsSet(
+        global.getAttributeNames().begin(), global.getAttributeNames().end());
+    for (auto &attr : global->getAttrs())
+      if (!elidedAttrsSet.contains(attr.getName().strref()))
+        g->setAttr(attr.getName(), attr.getValue());
+
     auto &gr = g.getInitializerRegion();
     rewriter.inlineRegionBefore(global.getRegion(), gr, gr.end());
     if (!gr.empty()) {

flang/lib/Optimizer/Dialect/FIROps.cpp

@@ -1308,6 +1308,9 @@ mlir::ParseResult fir::GlobalOp::parse(mlir::OpAsmParser &parser,
     simpleInitializer = true;
   }
 
+  if (parser.parseOptionalAttrDict(result.attributes))
+    return mlir::failure();
+
   if (succeeded(parser.parseOptionalKeyword("constant"))) {
     // if "constant" keyword then mark this as a constant, not a variable
     result.addAttribute("constant", builder.getUnitAttr());
@@ -1342,6 +1345,7 @@ void fir::GlobalOp::print(mlir::OpAsmPrinter &p) {
   p.printAttributeWithoutType(getSymrefAttr());
   if (auto val = getValueOrNull())
     p << '(' << val << ')';
+  p.printOptionalAttrDict((*this)->getAttrs(), (*this).getAttributeNames());
   if (getOperation()->getAttr(fir::GlobalOp::getConstantAttrNameStr()))
     p << " constant";
   if (getOperation()->getAttr(getTargetAttrName()))

flang/test/Fir/global-attributes.fir

@@ -0,0 +1,17 @@
+// RUN: fir-opt --fir-to-llvm-ir %s | FileCheck %s
+// RUN: tco --fir-to-llvm-ir %s | FileCheck %s
+// RUN: fir-opt %s | FileCheck %s --check-prefix=READ-OUT
+// RUN: tco --emit-fir %s | FileCheck %s --check-prefix=READ-OUT
+
+// CHECK: llvm.mlir.global external @_QMtest_0Edata_int() {{{.*}}test = "string_attribute_maintained"{{.*}}} : i32 {
+// CHECK: [[CST0:%.*]] = llvm.mlir.constant(10 : i32) : i32
+// CHECK: llvm.return [[CST0]] : i32
+// CHECK: }
+// READ-OUT: fir.global @_QMtest_0Edata_int {test = "string_attribute_maintained"} : i32 {
+// READ-OUT: %c10_i32 = arith.constant 10 : i32
+// READ-OUT: fir.has_value %c10_i32 : i32
+// READ-OUT: }
+fir.global @_QMtest_0Edata_int {test = "string_attribute_maintained"} : i32 {
+  %c10_i32 = arith.constant 10 : i32
+  fir.has_value %c10_i32 : i32
+}