[VM DBC compiler and simulator] Support reified generic functions.

runtime/vm/flow_graph_allocator.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #if !defined(DART_PRECOMPILED_RUNTIME)
 
 #include "vm/flow_graph_allocator.h"
 
 #include "vm/bit_vector.h"
 #include "vm/flow_graph.h"
@@ skipping 686 matching lines @@
       ConvertAllUses(range);
       return;
     }
 #endif  // defined(TARGET_ARCH_DBC)
     range->set_assigned_location(
         Location::StackSlot(slot_index, param->base_reg()));
     range->set_spill_slot(Location::StackSlot(slot_index, param->base_reg()));
 
   } else if (defn->IsSpecialParameter()) {
     SpecialParameterInstr* param = defn->AsSpecialParameter();
+    Location loc;
+#if defined(TARGET_ARCH_DBC)
+    intptr_t slot_index = flow_graph_.num_copied_params();
+    ASSERT(-flow_graph_.parsed_function().first_stack_local_index() - 1 ==
+           slot_index);
+    if ((param->kind() == SpecialParameterInstr::kContext) &&
+        (flow_graph_.parsed_function().function_type_arguments() != NULL)) {
+      // The first slot is used for function type arguments, either as their
+      // permanent location or as their temporary location when captured.
+      // So use the next one for the context.
+      slot_index++;

[regis, 2017/08/14 23:29:19]

If I remove this special handling on lines 712-718, i.e. if I never increment
slot_index, all tests pass. I do not understand why the context variable does
not collide with the type argument variable.

[Vyacheslav Egorov (Google), 2017/08/15 12:31:00]

Actually if you change stuff here you need also to change code in
runtime/vm/flow_graph_compiler_dbc.cc line 385 and further. They must match what
happens here. 

I am surprised it passes with storing context into completely different slot. 

Maybe there is no test that exercises both simultaneously?

[regis, 2017/08/15 22:01:53]

That was it. Thanks!
Yes, we have very few tests for generic functions, since only DDC is currently
supporting them.

+    }
+    loc = Location::RegisterLocation(slot_index);
+#else
     if (param->kind() == SpecialParameterInstr::kContext) {
-#if !defined(TARGET_ARCH_DBC)
-      const Register context_reg = CTX;
-#else
-      const intptr_t context_reg = flow_graph_.num_copied_params();
-#endif
+      loc = Location::RegisterLocation(CTX);
+    } else {
+      ASSERT(param->kind() == SpecialParameterInstr::kTypeArgs);
+      loc = Location::StackSlot(flow_graph_.num_copied_params(), FPREG);
+      range->set_assigned_location(loc);
+      range->set_spill_slot(loc);
+    }
+#endif  // defined(TARGET_ARCH_DBC)
 
+    if (loc.IsRegister()) {
       AssignSafepoints(defn, range);
-      range->finger()->Initialize(range);
-      range->set_assigned_location(Location::RegisterLocation(context_reg));
+      range->set_assigned_location(loc);
       if (range->End() > kNormalEntryPos) {
         LiveRange* tail = range->SplitAt(kNormalEntryPos);
         CompleteRange(tail, Location::kRegister);
       }
       ConvertAllUses(range);
       return;
     }
-    ASSERT(param->kind() == SpecialParameterInstr::kTypeArgs);
-#if defined(TARGET_ARCH_DBC)
-    UNIMPLEMENTED();
-#endif
-    const intptr_t slot_index = flow_graph_.num_copied_params();
-    range->set_assigned_location(Location::StackSlot(slot_index, FPREG));
-    range->set_spill_slot(Location::StackSlot(slot_index, FPREG));
   } else {
     ConstantInstr* constant = defn->AsConstant();
     ASSERT(constant != NULL);
     range->set_assigned_location(Location::Constant(constant));
     range->set_spill_slot(Location::Constant(constant));
   }
   AssignSafepoints(defn, range);
   range->finger()->Initialize(range);
   UsePosition* use =
       range->finger()->FirstRegisterBeneficialUse(block->start_pos());
@@ skipping 2272 matching lines @@
       printer.PrintBlocks();
 #endif
     }
     THR_Print("----------------------------------------------\n");
   }
 }
 
 }  // namespace dart
 
 #endif  // !defined(DART_PRECOMPILED_RUNTIME)