[Flang][OpenMP] Add some semantic checks for Linear clause (#111354)

This PR adds all the missing semantics for the Linear clause based on
the OpenMP 5.2 restrictions. The restriction details are mentioned
below.

OpenMP 5.2:
5.4.6 linear Clause restrictions
- A linear-modifier may be specified as ref or uval only on a declare
simd directive.
- If linear-modifier is not ref, all list items must be of type integer.
- If linear-modifier is ref or uval, all list items must be dummy
arguments without the VALUE attribute.
- List items must not be Cray pointers or variables that have the
POINTER attribute. Cray pointer support has been deprecated.
- If linear-modifier is ref, list items must be polymorphic variables,
assumed-shape arrays, or variables with the ALLOCATABLE attribute.
- A common block name must not appear in a linear clause.
- The list-item cannot appear more than once

4.4.4 ordered Clause restriction
- If n is explicitly specified, a linear clause must not be specified on
the same directive.

5.11 aligned Clause restriction
- Each list item must have C_PTR or Cray pointer type or have the
POINTER or ALLOCATABLE attribute. Cray pointer support has been
deprecated.

Author: Thirumalai-Shaktivel

flang/lib/Semantics/check-omp-structure.cpp

@@ -411,6 +411,19 @@ void OmpStructureChecker::CheckMultListItems() {
     CheckMultipleOccurrence(
         listVars, nontempNameList, clause->source, "NONTEMPORAL");
   }
+
+  // Linear clause
+  for (auto [_, clause] : FindClauses(llvm::omp::Clause::OMPC_linear)) {
+    const auto &linearClause{std::get<parser::OmpClause::Linear>(clause->u)};
+    std::list<parser::Name> nameList;
+    common::visit(
+        [&](const auto &u) {
+          std::copy(
+              u.names.begin(), u.names.end(), std::back_inserter(nameList));
+        },
+        linearClause.v.u);
+    CheckMultipleOccurrence(listVars, nameList, clause->source, "LINEAR");
+  }
 }
 
 bool OmpStructureChecker::HasInvalidWorksharingNesting(
@@ -2714,12 +2727,12 @@ void OmpStructureChecker::Leave(const parser::OmpClauseList &) {
         }
       }
     }
-
-    // Sema checks related to presence of multiple list items within the same
-    // clause
-    CheckMultListItems();
   } // SIMD
 
+  // Semantic checks related to presence of multiple list items within the same
+  // clause
+  CheckMultListItems();
+
   // 2.7.3 Single Construct Restriction
   if (GetContext().directive == llvm::omp::Directive::OMPD_end_single) {
     CheckNotAllowedIfClause(
@@ -3607,16 +3620,95 @@ void OmpStructureChecker::Enter(const parser::OmpClause::If &x) {
 void OmpStructureChecker::Enter(const parser::OmpClause::Linear &x) {
   CheckAllowedClause(llvm::omp::Clause::OMPC_linear);
 
+  parser::CharBlock source{GetContext().clauseSource};
   // 2.7 Loop Construct Restriction
   if ((llvm::omp::allDoSet | llvm::omp::allSimdSet)
           .test(GetContext().directive)) {
     if (std::holds_alternative<parser::OmpLinearClause::WithModifier>(x.v.u)) {
-      context_.Say(GetContext().clauseSource,
+      context_.Say(source,
           "A modifier may not be specified in a LINEAR clause "
           "on the %s directive"_err_en_US,
           ContextDirectiveAsFortran());
+      return;
+    }
+  }
+
+  // OpenMP 5.2: Ordered clause restriction
+  if (const auto *clause{
+          FindClause(GetContext(), llvm::omp::Clause::OMPC_ordered)}) {
+    const auto &orderedClause{std::get<parser::OmpClause::Ordered>(clause->u)};
+    if (orderedClause.v) {
+      return;
     }
   }
+
+  auto checkForValidLinearClause_01 = [&](const parser::Name &name,
+                                          bool is_ref) {
+    std::string listItemName{name.ToString()};
+    if (!is_ref && !name.symbol->GetType()->IsNumeric(TypeCategory::Integer)) {
+      context_.Say(source,
+          "The list item `%s` specified with other than linear-modifier `REF` must be of type INTEGER"_err_en_US,
+          listItemName);
+    }
+    if (GetContext().directive == llvm::omp::Directive::OMPD_declare_simd &&
+        !IsDummy(*name.symbol)) {
+      context_.Say(source,
+          "The list item `%s` must be a dummy argument"_err_en_US,
+          listItemName);
+    }
+    if (IsPointer(*name.symbol) ||
+        name.symbol->test(Symbol::Flag::CrayPointer)) {
+      context_.Say(source,
+          "The list item `%s` in a LINEAR clause must not be Cray Pointer or a variable with POINTER attribute"_err_en_US,
+          listItemName);
+    }
+    if (FindCommonBlockContaining(*name.symbol)) {
+      context_.Say(source,
+          "'%s' is a common block name and must not appear in an LINEAR clause"_err_en_US,
+          listItemName);
+    }
+  };
+
+  auto checkForValidLinearClause_02 = [&](const parser::Name &name,
+                                          const parser::OmpLinearModifier::Value
+                                              &modifierValue) {
+    std::string listItemName{name.ToString()};
+    checkForValidLinearClause_01(
+        name, (modifierValue == parser::OmpLinearModifier::Value::Ref));
+    if (modifierValue != parser::OmpLinearModifier::Value::Val &&
+        IsDummy(*name.symbol) && IsValue(*name.symbol)) {
+      context_.Say(source,
+          "The list item `%s` specified with the linear-modifier `REF` or `UVAL` must be a dummy argument without `VALUE` attribute"_err_en_US,
+          listItemName);
+    }
+    if (modifierValue == parser::OmpLinearModifier::Value::Ref &&
+        !(IsAllocatable(*name.symbol) || IsAssumedShape(*name.symbol) ||
+            IsPolymorphic(*name.symbol))) {
+      context_.Say(source,
+          "The list item `%s` specified with the linear-modifier `REF` must be polymorphic variable, assumed-shape array, or a variable with the `ALLOCATABLE` attribute"_err_en_US,
+          listItemName);
+    }
+  };
+
+  // OpenMP 5.2: Linear clause Restrictions
+  common::visit(
+      common::visitors{
+          [&](const parser::OmpLinearClause::WithoutModifier &withoutModifier) {
+            for (const auto &name : withoutModifier.names) {
+              if (name.symbol) {
+                checkForValidLinearClause_01(name, false);
+              }
+            }
+          },
+          [&](const parser::OmpLinearClause::WithModifier &withModifier) {
+            for (const auto &name : withModifier.names) {
+              if (name.symbol) {
+                checkForValidLinearClause_02(name, withModifier.modifier.v);
+              }
+            }
+          },
+      },
+      x.v.u);
 }
 
 void OmpStructureChecker::CheckAllowedMapTypes(

flang/test/Examples/omp-declarative-directive.f90

@@ -7,7 +7,7 @@
 ! 2.8.2 declare-simd
 
 subroutine declare_simd_1(a, b)
-  real(8), intent(inout) :: a, b
+  real(8), intent(inout), allocatable :: a, b
   !$omp declare simd(declare_simd_1) aligned(a)
   a = 3.14 + b
 end subroutine declare_simd_1

flang/test/Semantics/OpenMP/declarative-directive01.f90

@@ -23,6 +23,7 @@ end subroutine requires_2
 
 subroutine declare_simd_1(a, b)
   real(8), intent(inout) :: a, b
+  !ERROR: 'a' in ALIGNED clause must be of type C_PTR, POINTER or ALLOCATABLE
   !$omp declare simd(declare_simd_1) aligned(a)
   a = 3.14 + b
 end subroutine declare_simd_1

flang/test/Semantics/OpenMP/linear-clause01.f90

@@ -0,0 +1,45 @@
+! REQUIRES: openmp_runtime
+! RUN: %python %S/../test_errors.py %s %flang_fc1 %openmp_flags
+! OpenMP Version 5.2
+! Various checks for the linear clause
+! 5.4.6 `linear` Clause
+
+! Case 1
+subroutine linear_clause_01(arg)
+    integer, intent(in) :: arg(:)
+    !ERROR: A modifier may not be specified in a LINEAR clause on the DO directive
+    !$omp do linear(uval(arg))
+    do i = 1, 5
+        print *, arg(i)
+    end do
+end subroutine linear_clause_01
+
+! Case 2
+subroutine linear_clause_02(arg_01, arg_02)
+    !ERROR: The list item `arg_01` specified with other than linear-modifier `REF` must be of type INTEGER
+    !$omp declare simd linear(val(arg_01))
+    real, intent(in) :: arg_01(:)
+
+    !ERROR: The list item `arg_02` specified with the linear-modifier `REF` or `UVAL` must be a dummy argument without `VALUE` attribute
+    !$omp declare simd linear(uval(arg_02))
+    integer, value, intent(in) :: arg_02
+
+    !ERROR: The list item `var` must be a dummy argument
+    !ERROR: The list item `var` in a LINEAR clause must not be Cray Pointer or a variable with POINTER attribute
+    !$omp declare simd linear(uval(var))
+    integer, pointer :: var
+end subroutine linear_clause_02
+
+! Case 3
+subroutine linear_clause_03(arg)
+    integer, intent(in) :: arg
+    !ERROR: The list item `arg` specified with the linear-modifier `REF` must be polymorphic variable, assumed-shape array, or a variable with the `ALLOCATABLE` attribute
+    !ERROR: List item 'arg' present at multiple LINEAR clauses
+    !$omp declare simd linear(ref(arg)) linear(arg)
+
+    integer :: i
+    common /cc/ i
+    !ERROR: The list item `i` must be a dummy argument
+    !ERROR: 'i' is a common block name and must not appear in an LINEAR clause
+    !$omp declare simd linear(i)
+end subroutine linear_clause_03