[flang][hlfir] Fixed symbol lookup for character returns.

[vzakhari]

Summary

Symbols corresponding to entries returning character results
must be mapped to EmboxCharOp, first, before we can map them
to DeclareOp. The code may be reworked after HLFIR is enabled
by default, but right now it seems like an acceptable solution to me.

[jeanPerier]

Thanks, that looks good to me. Long term, we could maybe use a different map to store the MLIR block argument until they the specification are lowered and symbols can be fully mapped, but right now this would indeed be a sizable change with little reward.

[vzakhari]

Thank you, Jean!

flang/lib/Lower/Bridge.cpp

if (lowerToHighLevelFIR()) {
         auto exv =
             hlfir::translateToExtendedValue(toLocation(), *builder, *var);
         return exv.match(
             [](mlir::Value x) -> Fortran::lower::SymbolBox {
               return Fortran::lower::SymbolBox::Intrinsic{x};
             },
             [](auto x) -> Fortran::lower::SymbolBox { return x; });
       }
+
+      // Entry character result represented as an argument pair
+      // needs to be represented in the symbol table even before
+      // we can create DeclareOp for it. The temporary mapping
+      // is EmboxCharOp that conveys the address and length information.
+      // After mapSymbolAttributes is done, the mapping is replaced
+      // with the new DeclareOp, and the following table lookups
+      // do not reach here.
+      if (sym.IsFuncResult())
+        if (const Fortran::semantics::DeclTypeSpec *declTy = sym.GetType())
+          if (declTy->category() ==
+              Fortran::semantics::DeclTypeSpec::Category::Character)
+            return symMap->lookupSymbol(sym);
+
       // Procedure dummies are not mapped with an hlfir.declare because
       // they are not "variable" (cannot be assigned to), and it would
       // make hlfir.declare more complex than it needs to to allow this.
       // Do a regular lookup.
       if (Fortran::semantics::IsProcedure(sym))
         return symMap->lookupSymbol(sym);
       return {};
     }

flang/test/Lower/HLFIR/function-return.f90

character(5) function char_array_return()
   dimension :: char_array_return(10)
   char_array_return = "hello"
 end function
 ! CHECK-LABEL: func.func @_QPchar_array_return() -> !fir.array<10x!fir.char<1,5>> {
 ! CHECK:  %[[VAL_2:.*]] = fir.alloca !fir.array<10x!fir.char<1,5>>
 ! CHECK:  %[[VAL_4:.*]]:2 = hlfir.declare %[[VAL_2]]{{.*}} {uniq_name = "_QFchar_array_returnEchar_array_return"} : (!fir.ref<!fir.array<10x!fir.char<1,5>>>, !fir.shape<1>, index) -> (!fir.ref<!fir.array<10x!fir.char<1,5>>>, !fir.ref<!fir.array<10x!fir.char<1,5>>>)
 ! CHECK:  %[[VAL_5:.*]] = fir.load %[[VAL_4]]#1 : !fir.ref<!fir.array<10x!fir.char<1,5>>>
 ! CHECK:  return %[[VAL_5]] : !fir.array<10x!fir.char<1,5>>
+
+character*(*) function char_var_len_return()
+  character*(*) char_var_len_return2
+  entry char_var_len_return2
+end function char_var_len_return
+! CHECK-LABEL:   func.func @_QPchar_var_len_return(
+! CHECK-SAME:                                      %[[VAL_0:.*]]: !fir.ref<!fir.char<1,?>>,
+! CHECK-SAME:                                      %[[VAL_1:.*]]: index) -> !fir.boxchar<1> {
+! CHECK:           %[[VAL_2:.*]]:2 = hlfir.declare %[[VAL_0]] typeparams %[[VAL_1]] {uniq_name = "_QFchar_var_len_returnEchar_var_len_return"} : (!fir.ref<!fir.char<1,?>>, index) -> (!fir.boxchar<1>, !fir.ref<!fir.char<1,?>>)
+! CHECK:           %[[VAL_3:.*]]:2 = hlfir.declare %[[VAL_0]] typeparams %[[VAL_1]] {uniq_name = "_QFchar_var_len_returnEchar_var_len_return2"} : (!fir.ref<!fir.char<1,?>>, index) -> (!fir.boxchar<1>, !fir.ref<!fir.char<1,?>>)
+! CHECK:           cf.br ^bb1
+! CHECK:         ^bb1:
+! CHECK:           %[[VAL_4:.*]] = fir.emboxchar %[[VAL_2]]#1, %[[VAL_1]] : (!fir.ref<!fir.char<1,?>>, index) -> !fir.boxchar<1>
+! CHECK:           return %[[VAL_4]] : !fir.boxchar<1>
+! CHECK:         }
+
+! CHECK-LABEL:   func.func @_QPchar_var_len_return2(
+! CHECK-SAME:                                       %[[VAL_0:.*]]: !fir.ref<!fir.char<1,?>>,
+! CHECK-SAME:                                       %[[VAL_1:.*]]: index) -> !fir.boxchar<1> {
+! CHECK:           %[[VAL_2:.*]]:2 = hlfir.declare %[[VAL_0]] typeparams %[[VAL_1]] {uniq_name = "_QFchar_var_len_returnEchar_var_len_return"} : (!fir.ref<!fir.char<1,?>>, index) -> (!fir.boxchar<1>, !fir.ref<!fir.char<1,?>>)
+! CHECK:           %[[VAL_3:.*]]:2 = hlfir.declare %[[VAL_0]] typeparams %[[VAL_1]] {uniq_name = "_QFchar_var_len_returnEchar_var_len_return2"} : (!fir.ref<!fir.char<1,?>>, index) -> (!fir.boxchar<1>, !fir.ref<!fir.char<1,?>>)
+! CHECK:           cf.br ^bb1
+! CHECK:         ^bb1:
+! CHECK:           %[[VAL_4:.*]] = fir.emboxchar %[[VAL_3]]#1, %[[VAL_1]] : (!fir.ref<!fir.char<1,?>>, index) -> !fir.boxchar<1>
+! CHECK:           return %[[VAL_4]] : !fir.boxchar<1>
+! CHECK:         }