[flang][Semantics] Fix updating flags of threadprivate symbols in presence of default clause (#78283)

Current semantic checks of default clause incorrectly update symbol
flags related to threadprivate symbols. This patch adds an additional
check to skip such updation should a symbol be already declared
threadprivate.

Fixes #78282

Author: NimishMishra

flang/lib/Semantics/resolve-directives.cpp

@@ -2021,6 +2021,11 @@ void OmpAttributeVisitor::Post(const parser::Name &name) {
         }
       }
     }
+
+    if (Symbol * found{currScope().FindSymbol(name.source)}) {
+      if (found->test(semantics::Symbol::Flag::OmpThreadprivate))
+        return;
+    }
     std::vector<Symbol *> defaultDSASymbols;
     for (int dirDepth{0}; dirDepth < (int)dirContext_.size(); ++dirDepth) {
       DirContext &dirContext = dirContext_[dirDepth];

flang/test/Lower/OpenMP/default-clause.f90

@@ -383,3 +383,32 @@ subroutine skipped_default_clause_checks()
           iii=it(11)
        !$omp end parallel
 end subroutine
+
+!CHECK: func.func @_QPthreadprivate_with_default() {
+!CHECK: %[[VAR_I:.*]] = fir.alloca i32 {bindc_name = "i", uniq_name = "_QFthreadprivate_with_defaultEi"}
+!CHECK: %[[VAR_I_DECLARE:.*]] = hlfir.declare %[[VAR_I]] {uniq_name = "_QFthreadprivate_with_defaultEi"} : (!fir.ref<i32>) -> (!fir.ref<i32>, !fir.ref<i32>)
+!CHECK: %[[BLK_ADDR:.*]] = fir.address_of(@blk_) : !fir.ref<!fir.array<4xi8>>
+!CHECK: %[[BLK_THREADPRIVATE_OUTER:.*]] = omp.threadprivate %[[BLK_ADDR]] : !fir.ref<!fir.array<4xi8>> -> !fir.ref<!fir.array<4xi8>>
+!CHECK: %[[CONVERT:.*]] = fir.convert %[[BLK_THREADPRIVATE_OUTER]] : (!fir.ref<!fir.array<4xi8>>) -> !fir.ref<!fir.array<?xi8>>
+!CHECK: %[[VAR_C:.*]] = arith.constant 0 : index
+!CHECK: %[[BLK_REF:.*]] = fir.coordinate_of %[[CONVERT]], %[[VAR_C]] : (!fir.ref<!fir.array<?xi8>>, index) -> !fir.ref<i8>
+!CHECK: %[[CONVERT:.*]] = fir.convert %[[BLK_REF]] : (!fir.ref<i8>) -> !fir.ref<i32>
+!CHECK: %[[VAR_X_DECLARE:.*]] = hlfir.declare %[[CONVERT]] {uniq_name = "_QFthreadprivate_with_defaultEx"} : (!fir.ref<i32>) -> (!fir.ref<i32>, !fir.ref<i32>)
+!CHECK: omp.parallel {
+!CHECK:   %[[BLK_THREADPRIVATE_INNER:.*]] = omp.threadprivate %[[BLK_ADDR]] : !fir.ref<!fir.array<4xi8>> -> !fir.ref<!fir.array<4xi8>>
+!CHECK:   %[[CONVERT_INNER:.*]] = fir.convert %[[BLK_THREADPRIVATE_INNER]] : (!fir.ref<!fir.array<4xi8>>) -> !fir.ref<!fir.array<?xi8>>
+!CHECK:   %[[VAR_C_INNER:.*]] = arith.constant 0 : index
+!CHECK:   %[[BLK_REF_INNER:.*]] = fir.coordinate_of %[[CONVERT_INNER]], %[[VAR_C_INNER]] : (!fir.ref<!fir.array<?xi8>>, index) -> !fir.ref<i8>
+!CHECK:   %[[CONVERT_INNER:.*]] = fir.convert %[[BLK_REF_INNER]] : (!fir.ref<i8>) -> !fir.ref<i32>
+!CHECK:   %[[VAR_X_DECLARE_INNER:.*]] = hlfir.declare %[[CONVERT_INNER]] {uniq_name = "_QFthreadprivate_with_defaultEx"} : (!fir.ref<i32>) -> (!fir.ref<i32>, !fir.ref<i32>)
+subroutine threadprivate_with_default
+        integer :: x
+        common /blk/ x 
+        !$omp threadprivate (/blk/)
+
+        !$omp parallel do default(private)
+           do i = 1, 4
+              x = 4
+           end do
+        !$omp end parallel do
+end subroutine