[flang][OpenMP] Reuse semantic check for "constantness" of alignment

Use ScalarIntConstantExpr in the parse tree instead of ScalarIntExpr.
This will still parse a general expression, but the semantic checker
for expressions will automatically perfom a test for whether the value
is constant or not.

Use that instead of manual checks, it will make diagnostics more uniform.
There is no functional change other than that.

Author: kparzysz

flang/include/flang/Parser/parse-tree.h

@@ -4189,7 +4189,7 @@ struct OmpAffinityClause {
 
 // Ref: 5.2: [174]
 struct OmpAlignClause {
-  WRAPPER_CLASS_BOILERPLATE(OmpAlignClause, ScalarIntExpr);
+  WRAPPER_CLASS_BOILERPLATE(OmpAlignClause, ScalarIntConstantExpr);
 };
 
 // Ref: [4.5:72-81], [5.0:110-119], [5.1:134-143], [5.2:169-170]

flang/lib/Parser/openmp-parsers.cpp

@@ -1085,7 +1085,7 @@ TYPE_PARSER(construct<OmpBindClause>(
     "TEAMS" >> pure(OmpBindClause::Binding::Teams) ||
     "THREAD" >> pure(OmpBindClause::Binding::Thread)))
 
-TYPE_PARSER(construct<OmpAlignClause>(scalarIntExpr))
+TYPE_PARSER(construct<OmpAlignClause>(scalarIntConstantExpr))
 
 TYPE_PARSER(construct<OmpAtClause>(
     "EXECUTION" >> pure(OmpAtClause::ActionTime::Execution) ||

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

@@ -1540,9 +1540,8 @@ void OmpStructureChecker::Leave(const parser::OpenMPRequiresConstruct &) {
 
 void OmpStructureChecker::CheckAlignValue(const parser::OmpClause &clause) {
   if (auto *align{std::get_if<parser::OmpClause::Align>(&clause.u)}) {
-    if (const auto &v{GetIntValue(align->v)}; !v || *v <= 0) {
-      context_.Say(clause.source,
-          "The alignment value should be a constant positive integer"_err_en_US);
+    if (const auto &v{GetIntValue(align->v)}; v && *v <= 0) {
+      context_.Say(clause.source, "The alignment should be positive"_err_en_US);
     }
   }
 }

flang/test/Parser/OpenMP/allocate-align-tree.f90

@@ -26,14 +26,14 @@ end program allocate_align_tree
 !CHECK: | | ExecutionPartConstruct -> ExecutableConstruct -> OpenMPConstruct -> OpenMPExecutableAllocate
 !CHECK-NEXT: | | | Verbatim
 !CHECK-NEXT: | | | OmpObjectList -> OmpObject -> Designator -> DataRef -> Name = 'xarray'
-!CHECK-NEXT: | | | OmpClauseList -> OmpClause -> Align -> OmpAlignClause -> Scalar -> Integer -> Expr = '32_4'
+!CHECK-NEXT: | | | OmpClauseList -> OmpClause -> Align -> OmpAlignClause -> Scalar -> Integer -> Constant -> Expr = '32_4'
 !CHECK-NEXT: | | | | LiteralConstant -> IntLiteralConstant = '32'
 !CHECK-NEXT: | | | OmpClause -> Allocator -> Scalar -> Integer -> Expr = '2_8'
 !CHECK-NEXT: | | | | Designator -> DataRef -> Name = 'omp_large_cap_mem_alloc'
 !CHECK-NEXT: | | | OpenMPDeclarativeAllocate
 !CHECK-NEXT: | | | | Verbatim
 !CHECK-NEXT: | | | | OmpObjectList -> OmpObject -> Designator -> DataRef -> Name = 'j'
-!CHECK-NEXT: | | | | OmpClauseList -> OmpClause -> Align -> OmpAlignClause -> Scalar -> Integer -> Expr = '16_4'
+!CHECK-NEXT: | | | | OmpClauseList -> OmpClause -> Align -> OmpAlignClause -> Scalar -> Integer -> Constant -> Expr = '16_4'
 !CHECK-NEXT: | | | | | LiteralConstant -> IntLiteralConstant = '16'
 !CHECK-NEXT: | | | AllocateStmt
 

flang/test/Semantics/OpenMP/allocate-align01.f90

@@ -11,10 +11,10 @@ program allocate_align_tree
     integer :: z, t, xx
     t = 2
     z = 3
-    !ERROR: The alignment value should be a constant positive integer
+    !ERROR: Must be a constant value
 !$omp allocate(j) align(xx)
     !WARNING: The executable form of the OpenMP ALLOCATE directive has been deprecated, please use ALLOCATORS instead [-Wopen-mp-usage]
-    !ERROR: The alignment value should be a constant positive integer
+    !ERROR: The alignment should be positive
 !$omp allocate(xarray) align(-32) allocator(omp_large_cap_mem_alloc)
     allocate(j(z), xarray(t))
 end program allocate_align_tree