Handle the case of redeclared COMMON block

Author: eugeneepshteyn

flang/include/flang/Semantics/symbol.h

@@ -884,7 +884,7 @@ class Symbol {
   const Details &details() const { return details_; }
   // Assign the details of the symbol from one of the variants.
   // Only allowed in certain cases.
-  void set_details(Details &&);
+  void set_details(Details &&, bool force = false);
 
   // Can the details of this symbol be replaced with the given details?
   bool CanReplaceDetails(const Details &details) const;

flang/lib/Semantics/scope.cpp

@@ -145,6 +145,21 @@ void Scope::add_crayPointer(const SourceName &name, Symbol &pointer) {
 
 Symbol &Scope::MakeCommonBlock(SourceName name, SourceName location) {
   if (auto *cb{FindCB(name)}) {
+    if (cb->has<UseDetails>()) {
+      // COMMON blocks could be re-declared. Example:
+      //    module test
+      //      integer :: a
+      //      common /blk/ a
+      //    end module test
+      //    program main
+      //      use test          ! Initially get /blk/ with UseDetails
+      //      integer :: a1
+      //      common /blk/ a1   ! Update with CommonBlockDetails
+      //    end program main
+      // Reset details with real COMMON block details.
+      cb->set_details(CommonBlockDetails{name.empty() ? location : name},
+          /*force*/true);
+    }
     return *cb;
   } else {
     Symbol &symbol{MakeSymbol(

flang/lib/Semantics/symbol.cpp

@@ -317,8 +317,10 @@ std::string DetailsToString(const Details &details) {
 
 std::string Symbol::GetDetailsName() const { return DetailsToString(details_); }
 
-void Symbol::set_details(Details &&details) {
-  CHECK(CanReplaceDetails(details));
+void Symbol::set_details(Details &&details, bool force) {
+  if (!force) {
+    CHECK(CanReplaceDetails(details));
+  }
   details_ = std::move(details);
 }