[flang] do not finalize or initialize unused entry dummy (llvm#125482)

Dummy arguments from other entry statement that are not live in the current entry have no backing storage, user code referring to them is not allowed to be reached. The compiler was generating initialization/destruction code for them when INTENT(OUT), causing undefined behaviors.

Author: jeanPerier

flang/lib/Lower/ConvertVariable.cpp

@@ -956,7 +956,15 @@ static void instantiateLocal(Fortran::lower::AbstractConverter &converter,
                              Fortran::lower::SymMap &symMap) {
   assert(!var.isAlias());
   Fortran::lower::StatementContext stmtCtx;
+  // isUnusedEntryDummy must be computed before mapSymbolAttributes.
+  const bool isUnusedEntryDummy =
+      var.hasSymbol() && Fortran::semantics::IsDummy(var.getSymbol()) &&
+      !symMap.lookupSymbol(var.getSymbol()).getAddr();
   mapSymbolAttributes(converter, var, symMap, stmtCtx);
+  // Do not generate code to initialize/finalize/destroy dummy arguments that
+  // are nor part of the current ENTRY. They do not have backing storage.
+  if (isUnusedEntryDummy)
+    return;
   deallocateIntentOut(converter, var, symMap);
   if (needDummyIntentoutFinalization(var))
     finalizeAtRuntime(converter, var, symMap);
@@ -999,7 +1007,6 @@ static void instantiateLocal(Fortran::lower::AbstractConverter &converter,
                "trying to deallocate entity not lowered as allocatable");
         Fortran::lower::genDeallocateIfAllocated(*converterPtr, *mutableBox,
                                                  loc, sym);
-        
       });
     }
   }

flang/test/Lower/entry-statement-init.f90

@@ -0,0 +1,26 @@
+! RUN: bbc -emit-hlfir -o - %s | FileCheck %s
+
+! Test initialization and finalizations of dummy arguments in entry statements.
+
+module m
+  type t
+  end type
+contains
+ subroutine test1(x)
+   class(t), intent(out) :: x
+   entry test1_entry()
+ end subroutine
+ subroutine test2(x)
+   class(t), intent(out) :: x
+   entry test2_entry(x)
+ end subroutine
+end module
+! CHECK-LABEL:   func.func @_QMmPtest1_entry(
+! CHECK-NOT: Destroy
+! CHECK-NOT: Initialize
+! CHECK:           return
+
+! CHECK-LABEL:   func.func @_QMmPtest2_entry(
+! CHECK: Destroy
+! CHECK: Initialize
+! CHECK:           return