[flang] Set initial size and type code for unlimited polymorphic descriptor

[clementval]

Summary

Initialization of unlimited polymorphic descriptor was raising an error.
This patch sets a default size and type code for unlimited polymoprhic descriptor
that will be updated once allocated/assigned.

[PeteSteinfeld]

All builds and tests correctly and looks good.

flang/lib/Optimizer/CodeGen/CodeGen.cpp

std::tuple<mlir::Value, mlir::Value> getSizeAndTypeCode(
     }
     // Reference type.
     if (fir::isa_ref_type(boxEleTy)) {
       auto ptrTy = mlir::LLVM::LLVMPointerType::get(
           mlir::LLVM::LLVMVoidType::get(rewriter.getContext()));
       mlir::Value size = genTypeStrideInBytes(loc, i64Ty, rewriter, ptrTy);
       return {size, this->genConstantOffset(loc, rewriter, CFI_type_cptr)};
     }
+    // Unlimited polymorphic or assumed type. Use 0 and CFI_type_other since the
+    // information is not none at this point.
+    if (boxEleTy.isa<mlir::NoneType>())
+      return {rewriter.create<mlir::LLVM::ConstantOp>(loc, i64Ty, 0),
+              this->genConstantOffset(loc, rewriter, CFI_type_other)};
     fir::emitFatalError(loc, "unhandled type in fir.box code generation");
   }
 
   /// Basic pattern to write a field in the descriptor
   mlir::Value insertField(mlir::ConversionPatternRewriter &rewriter,
                           mlir::Location loc, mlir::Value dest,
                           llvm::ArrayRef<std::int64_t> fldIndexes,
                           mlir::Value value, bool bitcast = false) const {

flang/test/Fir/polymorphic.fir

+// RUN: tco %s | FileCheck %s
+
+// Test code gen for unlimited polymorphic type descriptor.
+
+func.func @_QMpolymorphic_testPtest_allocate_unlimited_polymorphic_non_derived() {
+  %0 = fir.alloca !fir.class<!fir.ptr<none>> {bindc_name = "u", uniq_name = "_QMpolymorphic_testFtest_allocate_unlimited_polymorphic_non_derivedEu"}
+  %1 = fir.zero_bits !fir.ptr<none>
+  %2 = fir.embox %1 : (!fir.ptr<none>) -> !fir.class<!fir.ptr<none>>
+  fir.store %2 to %0 : !fir.ref<!fir.class<!fir.ptr<none>>>
+  return
+}
+
+// CHECK-LABEL: define void @_QMpolymorphic_testPtest_allocate_unlimited_polymorphic_non_derived() {
+// CHECK:   %[[MEM:.*]] = alloca { ptr, i64, i32, i8, i8, i8, i8 }
+// CHECK:   %[[DESC:.*]] = alloca { ptr, i64, i32, i8, i8, i8, i8 }, i64 1
+// CHECK:   store { ptr, i64, i32, i8, i8, i8, i8 } { ptr null, i64 0, i32 20180515, i8 0, i8 -1, i8 1, i8 0 }, ptr %[[MEM]]
+// CHECK:   %[[LOADED:.*]] = load { ptr, i64, i32, i8, i8, i8, i8 }, ptr %[[MEM]], align 8
+// CHECK:   store { ptr, i64, i32, i8, i8, i8, i8 } %[[LOADED]], ptr %[[DESC]]
+// CHECK:   ret void
+// CHECK: }