[flang] Use 0 for unknown function pointer result length. (llvm#97035)

Author: vzakhari

flang/lib/Lower/ConvertProcedureDesignator.cpp

@@ -89,9 +89,15 @@ fir::ExtendedValue Fortran::lower::convertProcedureDesignator(
             fir::factory::genMaxWithZero(builder, loc, rawLen);
       }
     }
+    // The caller of the function pointer will have to allocate
+    // the function result with the character length specified
+    // by the boxed value. If the result length cannot be
+    // computed statically, set it to zero (we used to use -1,
+    // but this could cause assertions in LLVM after inlining
+    // exposed alloca of size -1).
     if (!funcPtrResultLength)
       funcPtrResultLength = builder.createIntegerConstant(
-          loc, builder.getCharacterLengthType(), -1);
+          loc, builder.getCharacterLengthType(), 0);
     return fir::CharBoxValue{funcPtr, funcPtrResultLength};
   }
   return funcPtr;

flang/test/Lower/HLFIR/procedure-pointer.f90

@@ -128,7 +128,7 @@ subroutine  sub4()
 ! CHECK: fir.store %[[VAL_2]] to %[[VAL_0]] : !fir.ref<!fir.boxproc<(!fir.ref<i32>) -> !fir.box<!fir.ptr<!fir.char<1,?>>>>>
 ! CHECK: %[[VAL_3:.*]]:2 = hlfir.declare %[[VAL_0]] {fortran_attrs = #fir.var_attrs<pointer>, uniq_name = "_QFsub4Ep2"} : (!fir.ref<!fir.boxproc<(!fir.ref<i32>) -> !fir.box<!fir.ptr<!fir.char<1,?>>>>>) -> (!fir.ref<!fir.boxproc<(!fir.ref<i32>) -> !fir.box<!fir.ptr<!fir.char<1,?>>>>>, !fir.ref<!fir.boxproc<(!fir.ref<i32>) -> !fir.box<!fir.ptr<!fir.char<1,?>>>>>)
 ! CHECK: %[[VAL_4:.*]] = fir.address_of(@_QPchar_func) : (!fir.ref<i32>) -> !fir.box<!fir.ptr<!fir.char<1,?>>>
-! CHECK: %[[VAL_12:.*]] = arith.constant -1 : index
+! CHECK: %[[VAL_12:.*]] = arith.constant 0 : index
 ! CHECK: %[[VAL_5:.*]] = fir.emboxproc %[[VAL_4]] : ((!fir.ref<i32>) -> !fir.box<!fir.ptr<!fir.char<1,?>>>) -> !fir.boxproc<() -> ()>
 ! CHECK: %[[VAL_6:.*]] = fir.convert %[[VAL_12]] : (index) -> i64
 ! CHECK: %[[VAL_7:.*]] = fir.undefined tuple<!fir.boxproc<() -> ()>, i64>
@@ -375,7 +375,7 @@ subroutine takes_opt_proc_ptr(p)
 
 ! CHECK-LABEL: fir.global internal @_QFsub1Ep7 : !fir.boxproc<(!fir.ref<i32>) -> !fir.box<!fir.ptr<!fir.char<1,?>>>> {
 ! CHECK: %[[VAL_0:.*]] = fir.address_of(@_QPchar_func) : (!fir.ref<i32>) -> !fir.box<!fir.ptr<!fir.char<1,?>>>
-! CHECK: %[[VAL_11:.*]] = arith.constant -1 : index
+! CHECK: %[[VAL_11:.*]] = arith.constant 0 : index
 ! CHECK: %[[VAL_1:.*]] = fir.emboxproc %[[VAL_0]] : ((!fir.ref<i32>) -> !fir.box<!fir.ptr<!fir.char<1,?>>>) -> !fir.boxproc<() -> ()>
 ! CHECK: %[[VAL_2:.*]] = fir.convert %[[VAL_11]] : (index) -> i64
 ! CHECK: %[[VAL_3:.*]] = fir.undefined tuple<!fir.boxproc<() -> ()>, i64>

flang/test/Lower/dummy-procedure-character.f90

@@ -82,7 +82,7 @@ function bar4(n)
     end function
   end interface
 ! CHECK:  %[[VAL_0:.*]] = fir.address_of(@_QPbar4) : (!fir.ref<!fir.char<1,?>>, index, !fir.ref<i32>) -> !fir.boxchar<1>
-! CHECK:  %[[VAL_1:.*]] = arith.constant -1 : index
+! CHECK:  %[[VAL_1:.*]] = arith.constant 0 : index
 ! CHECK:  %[[VAL_2:.*]] = fir.emboxproc %[[VAL_0]] : ((!fir.ref<!fir.char<1,?>>, index, !fir.ref<i32>) -> !fir.boxchar<1>) -> !fir.boxproc<() -> ()>
 ! CHECK:  %[[VAL_3:.*]] = fir.convert %[[VAL_1]] : (index) -> i64
 ! CHECK:  %[[VAL_4:.*]] = fir.undefined tuple<!fir.boxproc<() -> ()>, i64>
@@ -97,7 +97,7 @@ subroutine cannot_compute_len_yet_2()
   character(*) :: bar5
   external :: bar5
 ! CHECK:  %[[VAL_0:.*]] = fir.address_of(@_QPbar5) : (!fir.ref<!fir.char<1,?>>, index) -> !fir.boxchar<1>
-! CHECK:  %[[VAL_1:.*]] = arith.constant -1 : index
+! CHECK:  %[[VAL_1:.*]] = arith.constant 0 : index
 ! CHECK:  %[[VAL_2:.*]] = fir.emboxproc %[[VAL_0]] : ((!fir.ref<!fir.char<1,?>>, index) -> !fir.boxchar<1>) -> !fir.boxproc<() -> ()>
 ! CHECK:  %[[VAL_3:.*]] = fir.convert %[[VAL_1]] : (index) -> i64
 ! CHECK:  %[[VAL_4:.*]] = fir.undefined tuple<!fir.boxproc<() -> ()>, i64>