[turbofan] put gaps before instructions

src/compiler/register-allocator.cc

Index: src/compiler/register-allocator.cc
diff --git a/src/compiler/register-allocator.cc b/src/compiler/register-allocator.cc
index a9cdf51b5636d7d2d0f484c6e2e36875e89cf3c9..61afa54d0a04374428e07fa348af3dd0ccb4f54f 100644
--- a/src/compiler/register-allocator.cc
+++ b/src/compiler/register-allocator.cc
@@ -1078,9 +1078,8 @@ void RegisterAllocator::ProcessPhis(const InstructionBlock* block) {
     auto output = phi->output();
     int phi_vreg = phi->virtual_register();
     LiveRange* live_range = LiveRangeFor(phi_vreg);
-    BlockStartInstruction* block_start =
-        code()->GetBlockStart(block->rpo_number());
-    block_start->GetOrCreateParallelMove(GapInstruction::BEFORE, code_zone())
+    GapInstruction* gap = code()->GapAt(block->code_start() + 1);
+    gap->GetOrCreateParallelMove(GapInstruction::BEFORE, code_zone())
         ->AddMove(output, live_range->GetSpillOperand(), code_zone());
     live_range->SetSpillStartIndex(block->first_instruction_index());
   }
@@ -1346,14 +1345,11 @@ void RegisterAllocator::ResolveControlFlow(const InstructionBlock* block,
   if (pred_op->Equals(cur_op)) return;
   GapInstruction* gap = nullptr;
   if (block->PredecessorCount() == 1) {
-    gap = code()->GapAt(block->first_instruction_index());
+    gap = code()->GapAt(block->first_instruction_index() + 1);
   } else {
     DCHECK(pred->SuccessorCount() == 1);
     gap = GetLastGap(pred);
-
-    Instruction* branch = InstructionAt(pred->last_instruction_index());
-    DCHECK(!branch->HasPointerMap());
-    USE(branch);
+    DCHECK(!InstructionAt(pred->last_instruction_index())->HasPointerMap());
   }
   gap->GetOrCreateParallelMove(GapInstruction::START, code_zone())
       ->AddMove(pred_op, cur_op, code_zone());