[Flang] Don't crash when BOZ literals are on the rhs of an assignment

[PeteSteinfeld]

Summary

For BOZ literals, the rhsType will be empty. Check for that before
trying to access its value.

[clementval]

flang/lib/Lower/Bridge.cpp

2878–2879

Thanks for the fix Pete. Can we combine this in a single if?

[PeteSteinfeld]

Combining two "if"s into a single one as per @clementval's suggestion.

[clementval]

flang/lib/Lower/Bridge.cpp

2864–2865

The rhsType check should only apply to the rhsType->IsPolymorphic() || rhsType->IsUnlimitedPolymorphic() part. If lhsType is polymorphic but the rhsType is typeless, we still want to lower to the assign runtime function.

[PeteSteinfeld]

Responding to more guidance from @clementval.

[PeteSteinfeld]

flang/lib/Lower/Bridge.cpp

2864–2865

Thanks, @clementval!

[clementval]

LGTM

[jeanPerier]

LGTM

flang/lib/Lower/Bridge.cpp

std::visit(
               assert(lhsType && "lhs cannot be typeless");
               std::optional<Fortran::evaluate::DynamicType> rhsType =
                   assign.rhs.GetType();
 
               // Assignment to/from polymorphic entities are done with the
               // runtime.
               if (lhsType->IsPolymorphic() ||
                   lhsType->IsUnlimitedPolymorphic() ||
-                  rhsType->IsPolymorphic() ||
-                  rhsType->IsUnlimitedPolymorphic()) {
+                  (rhsType && (rhsType->IsPolymorphic() ||
+                               rhsType->IsUnlimitedPolymorphic()))) {
                 mlir::Value lhs;
                 if (Fortran::lower::isWholeAllocatable(assign.lhs))
                   lhs = genExprMutableBox(loc, assign.lhs).getAddr();
                 else
                   lhs = fir::getBase(genExprBox(loc, assign.lhs, stmtCtx));
                 mlir::Value rhs =
                     fir::getBase(genExprBox(loc, assign.rhs, stmtCtx));
                 fir::runtime::genAssign(*builder, loc, lhs, rhs);
                 return;
               }
 
               // Note: No ad-hoc handling for pointers is required here. The
               // target will be assigned as per 2018 10.2.1.3 p2. genExprAddr
               // on a pointer returns the target address and not the address of
               // the pointer variable.
 
               if (assign.lhs.Rank() > 0 || explicitIterationSpace()) {
                 if (isDerivedCategory(lhsType->category()) &&
                     Fortran::semantics::IsFinalizable(
                         lhsType->GetDerivedTypeSpec()))
                   TODO(loc, "derived-type finalization with array assignment");
                 // Array assignment