[flang] Make sure derived-type finalization is done before return

[clementval]

Summary

Finalization needs to be done before the terminator. In case
of end program, this was done after it and trigger a verifier error.
This patch fixes this case.

[jeanPerier]

Would it also work to make genFIR(const Fortran::parser::EndProgramStmt &) { genExitRoutine(); } a no-op and centralize dealing with exits in endNewFunction ?
That way, it seems it would not be needed to do any special case (EndSubroutineStmt and the others are all nops I think).

BTW, there is a genExitRoutine call in case of early returns (Fortran::parser::ReturnStmt) here: https://github.com/llvm/llvm-project/blob/main/flang/lib/Lower/Bridge.cpp#L3062
Does it fits with finalizations ?

[jeanPerier]

Approving this fix for now since this is fixing regressions, my suggestion can be revisited/tested in another patch.

[clementval]

In D143055#4096312, @jeanPerier wrote:

Would it also work to make genFIR(const Fortran::parser::EndProgramStmt &) { genExitRoutine(); } a no-op and centralize dealing with exits in endNewFunction ?
That way, it seems it would not be needed to do any special case (EndSubroutineStmt and the others are all nops I think).

Yes it works and make things simpler. I have made a new diff here D143065.

BTW, there is a genExitRoutine call in case of early returns (Fortran::parser::ReturnStmt) here: https://github.com/llvm/llvm-project/blob/main/flang/lib/Lower/Bridge.cpp#L3062
Does it fits with finalizations ?

We need a bridge.fctCtx().finalizeAndKeep(); before generating the return. It's added to the same patch

flang/lib/Lower/Bridge.cpp

void maybeStartBlock(mlir::Block *newBlock) {
     if (newBlock)
       startBlock(newBlock);
   }
 
   /// Finish translation of a function.
   void endNewFunction(Fortran::lower::pft::FunctionLikeUnit &funit) {
     setCurrentPosition(Fortran::lower::pft::stmtSourceLoc(funit.endStmt));
     if (funit.isMainProgram()) {
+      if (!blockIsUnterminated()) {
+        auto insertPt = builder->saveInsertionPoint();
+        mlir::Block *currentBlock = builder->getBlock();
+        builder->setInsertionPoint(&currentBlock->back());
+        bridge.fctCtx().finalizeAndPop();
+        builder->restoreInsertionPoint(insertPt);
+      } else {
         bridge.fctCtx().finalizeAndPop();
         genExitRoutine();
+      }
     } else {
       genFIRProcedureExit(funit, funit.getSubprogramSymbol());
     }
     funit.finalBlock = nullptr;
     LLVM_DEBUG(llvm::dbgs() << "\n[bridge - endNewFunction";
                if (auto *sym = funit.scope->symbol()) llvm::dbgs()
                << " " << sym->name();
                llvm::dbgs() << "] generated IR:\n\n"

flang/test/Lower/derived-type-finalization.f90

 ! CHECK-LABEL: func.func @_QMderived_type_finalizationPtest_finalize_intent_out(
 ! CHECK-SAME: %[[T:.*]]: !fir.ref<!fir.type<_QMderived_type_finalizationTt1{a:i32}>> {fir.bindc_name = "t"}) {
 ! CHECK: %[[EMBOX:.*]] = fir.embox %[[T]] : (!fir.ref<!fir.type<_QMderived_type_finalizationTt1{a:i32}>>) -> !fir.box<!fir.type<_QMderived_type_finalizationTt1{a:i32}>>
 ! CHECK: %[[BOX_NONE:.*]] = fir.convert %[[EMBOX]] : (!fir.box<!fir.type<_QMderived_type_finalizationTt1{a:i32}>>) -> !fir.box<none>
 ! CHECK: %{{.*}} = fir.call @_FortranADestroy(%[[BOX_NONE]]) {{.*}}: (!fir.box<none>) -> none
 ! CHECK: return
 
 end module
+
+program p
+  use derived_type_finalization
+  type(t1) :: t
+  print *, 'end of program'
+end program
+
+! CHECK-LABEL: func.func @_QQmain() {
+! CHECK: %[[T:.*]] = fir.alloca !fir.type<_QMderived_type_finalizationTt1{a:i32}> {bindc_name = "t", uniq_name = "_QFEt"}
+! CHECK: %[[EMBOX:.*]] = fir.embox %[[T]] : (!fir.ref<!fir.type<_QMderived_type_finalizationTt1{a:i32}>>) -> !fir.box<!fir.type<_QMderived_type_finalizationTt1{a:i32}>>
+! CHECK: %[[BOX_NONE:.*]] = fir.convert %[[EMBOX]] : (!fir.box<!fir.type<_QMderived_type_finalizationTt1{a:i32}>>) -> !fir.box<none>
+! CHECK: %{{.*}} = fir.call @_FortranADestroy(%[[BOX_NONE]]) {{.*}} : (!fir.box<none>) -> none
+! CHECK: return