[flang] Fix semantic analysis for "forall" targeted by "label"

[peixin]

Summary

As Fortran 2018 3.18, the branch target statement can be
forall-construct-stmt, but cannot be forall-stmt. forall-stmt is
wrapped by Statement in action-stmt and action-stmt can be one
branch target statement. Fix the semantic analysis and add two
regression test cases in lowering.

[jeanPerier]

LGTM

[peixin]

@jeanPerier Do I need to check-pick this to fir-dev?

[jeanPerier]

@jeanPerier Do I need to check-pick this to fir-dev?

Semantics single point of truth is LLVM. We cherry-pick semantic changes from time to time so that end to end testing can benefit from the fixes unit lowering upstreaming is finished.
So, it is nicer if do, but it is not critical (as opposed to all changes to lowering that must be synced back to fir-dev because we still consider it as the source of truth for lowering).

[peixin]

@jeanPerier Got it. Thanks for the explanation. I will leave this in LLVM. It can be cherry-picked together with others from time to time to save our time.

flang/lib/Semantics/resolve-labels.cpp

if (std::is_same_v<A, parser::ActionStmt> ||
       std::is_same_v<A, parser::NonLabelDoStmt> ||
       std::is_same_v<A, parser::EndDoStmt> ||
       std::is_same_v<A, common::Indirection<parser::EndDoStmt>> ||
       std::is_same_v<A, parser::BlockStmt> ||
       std::is_same_v<A, parser::EndBlockStmt> ||
       std::is_same_v<A, parser::CriticalStmt> ||
       std::is_same_v<A, parser::EndCriticalStmt> ||
       std::is_same_v<A, parser::ForallConstructStmt> ||
-      std::is_same_v<A, parser::ForallStmt> ||
       std::is_same_v<A, parser::WhereConstructStmt> ||
       std::is_same_v<A, parser::EndFunctionStmt> ||
       std::is_same_v<A, parser::EndMpSubprogramStmt> ||
       std::is_same_v<A, parser::EndProgramStmt> ||
       std::is_same_v<A, parser::EndSubroutineStmt>) {
     return Legality::always;
   } else {
     return Legality::never;
template <typename A> bool Pre(const parser::Statement<A> &statement) {
     const auto &label = statement.label;
     if (!label) {
       return true;
     }
     using LabeledConstructStmts = std::tuple<parser::AssociateStmt,
         parser::BlockStmt, parser::ChangeTeamStmt, parser::CriticalStmt,
         parser::IfThenStmt, parser::NonLabelDoStmt, parser::SelectCaseStmt,
         parser::SelectRankStmt, parser::SelectTypeStmt,
-        parser::WhereConstructStmt>;
+        parser::ForallConstructStmt, parser::WhereConstructStmt>;
     using LabeledConstructEndStmts = std::tuple<parser::EndAssociateStmt,
         parser::EndBlockStmt, parser::EndChangeTeamStmt,
         parser::EndCriticalStmt, parser::EndDoStmt, parser::EndForallStmt,
         parser::EndIfStmt, parser::EndSelectStmt, parser::EndWhereStmt>;
     using LabeledProgramUnitEndStmts =
         std::tuple<parser::EndFunctionStmt, parser::EndMpSubprogramStmt,
             parser::EndProgramStmt, parser::EndSubroutineStmt>;
     auto targetFlags{ConstructBranchTargetFlags(statement)};

flang/test/Lower/forall/forall-construct-4.f90

+! Test forall lowering
+
+! RUN: bbc -emit-fir %s -o - | FileCheck %s
+
+!*** Test forall targeted by label
+subroutine test4_forall_construct()
+      integer :: a(2) = 1
+100   forall (i=1:2)
+        a(i) = a(i) + 1
+      end forall
+      if (a(1) > 3) goto 200
+      goto 100
+200   return
+end subroutine test4_forall_construct
+
+! CHECK-LABEL: func @_QPtest4_forall_construct
+! CHECK:   cf.br ^bb1
+! CHECK: ^bb1:  // 2 preds: ^bb0, ^bb2
+! CHECK:   %{{.*}} = fir.do_loop
+! CHECK:   cf.cond_br %{{.*}}, ^bb2, ^bb3
+! CHECK: ^bb2:  // pred: ^bb1
+! CHECK:   cf.br ^bb1
+! CHECK: ^bb3:  // pred: ^bb1
+! CHECK:   cf.br ^bb4
+! CHECK: ^bb4:  // pred: ^bb3
+! CHECK:   return
+
+subroutine test4_forall_construct2()
+      integer :: a(2) = 1
+100   forall (i=1:2) a(i) = a(i) + 1
+      if (a(1) > 3) goto 200
+      goto 100
+200   return
+end subroutine test4_forall_construct2
+
+! CHECK-LABEL: func @_QPtest4_forall_construct2
+! CHECK:   cf.br ^bb1
+! CHECK: ^bb1:  // 2 preds: ^bb0, ^bb2
+! CHECK:   %{{.*}} = fir.do_loop
+! CHECK:   cf.cond_br %{{.*}}, ^bb2, ^bb3
+! CHECK: ^bb2:  // pred: ^bb1
+! CHECK:   cf.br ^bb1
+! CHECK: ^bb3:  // pred: ^bb1
+! CHECK:   cf.br ^bb4
+! CHECK: ^bb4:  // pred: ^bb3
+! CHECK:   return