[turbofan] simplify gap ordering

src/compiler/register-allocator.cc

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/compiler/linkage.h"
 #include "src/compiler/register-allocator.h"
 #include "src/string-stream.h"
 
 namespace v8 {
 namespace internal {
@@ skipping 1060 matching lines @@
       if (output->IsStackSlot()) {
         DCHECK(output->index() < 0);
         range->SetSpillOperand(output);
         range->SetSpillStartIndex(end);
         assigned = true;
       }
 
       for (auto succ : block->successors()) {
         const InstructionBlock* successor = code()->InstructionBlockAt(succ);
         DCHECK(successor->PredecessorCount() == 1);
-        int gap_index = successor->first_instruction_index() + 1;
+        int gap_index = successor->first_instruction_index();
         DCHECK(code()->IsGapAt(gap_index));
 
         // Create an unconstrained operand for the same virtual register
         // and insert a gap move from the fixed output to the operand.
         UnallocatedOperand* output_copy =
             new (code_zone()) UnallocatedOperand(UnallocatedOperand::ANY);
         output_copy->set_virtual_register(output_vreg);
 
         AddGapMove(gap_index, GapInstruction::START, output, output_copy);
       }
     }
 
     if (!assigned) {
       for (auto succ : block->successors()) {
         const InstructionBlock* successor = code()->InstructionBlockAt(succ);
         DCHECK(successor->PredecessorCount() == 1);
-        int gap_index = successor->first_instruction_index() + 1;
+        int gap_index = successor->first_instruction_index();
         range->SpillAtDefinition(local_zone(), gap_index, output);
         range->SetSpillStartIndex(gap_index);
       }
     }
   }
 }
 
 
 void RegisterAllocator::MeetConstraintsBetween(Instruction* first,
                                                Instruction* second,
@@ skipping 1260 matching lines @@
         InactiveToHandled(range);
         --i;
       }
     }
   }
 }
 
 
 bool RegisterAllocator::IsBlockBoundary(LifetimePosition pos) {
   return pos.IsInstructionStart() &&
-         InstructionAt(pos.InstructionIndex())->IsBlockStart();
+         code()->GetInstructionBlock(pos.InstructionIndex())->code_start() ==
+             pos.InstructionIndex();
 }
 
 
 LiveRange* RegisterAllocator::SplitRangeAt(LiveRange* range,
                                            LifetimePosition pos) {
   DCHECK(!range->IsFixed());
   TraceAlloc("Splitting live range %d at %d\n", range->id(), pos.Value());
 
   if (pos.Value() <= range->Start().Value()) return range;
 
@@ skipping 77 matching lines @@
                                           LifetimePosition until,
                                           LifetimePosition end) {
   CHECK(start.Value() < end.Value());
   auto second_part = SplitRangeAt(range, start);
   if (!AllocationOk()) return;
 
   if (second_part->Start().Value() < end.Value()) {
     // The split result intersects with [start, end[.
     // Split it at position between ]start+1, end[, spill the middle part
     // and put the rest to unhandled.
+    auto third_part_end = end.PrevInstruction().InstructionEnd();
+    if (IsBlockBoundary(end.InstructionStart())) {
+      third_part_end = end.InstructionStart();
+    }
     auto third_part = SplitBetween(
         second_part, Max(second_part->Start().InstructionEnd(), until),
-        end.PrevInstruction().InstructionEnd());
+        third_part_end);
     if (!AllocationOk()) return;
 
     DCHECK(third_part != second_part);
 
     Spill(second_part);
     AddToUnhandledSorted(third_part);
   } else {
     // The split result does not intersect with [start, end[.
     // Nothing to spill. Just put it to unhandled as whole.
     AddToUnhandledSorted(second_part);
@@ skipping 49 matching lines @@
   } else {
     DCHECK(range->Kind() == GENERAL_REGISTERS);
     assigned_registers_->Add(reg);
   }
   range->set_assigned_register(reg, code_zone());
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8