Add support for fixed parameters in the register allocator.

runtime/vm/flow_graph_allocator.cc

Index: runtime/vm/flow_graph_allocator.cc
diff --git a/runtime/vm/flow_graph_allocator.cc b/runtime/vm/flow_graph_allocator.cc
index ec48c20003803d5cb19a44a57421b8dd1584367a..0dae11236cd140eafc208a4b5251cdc425118cc9 100644
--- a/runtime/vm/flow_graph_allocator.cc
+++ b/runtime/vm/flow_graph_allocator.cc
@@ -139,6 +139,17 @@ void FlowGraphAllocator::ComputeInitialSets() {
     }
   }
 
+  // Process incomming parameters.

[srdjan, 2012/07/26 00:33:56]

s/incomming/incoming/

[Vyacheslav Egorov (Google), 2012/07/26 11:33:53]

Done.

+  GraphEntryInstr* graph_entry = postorder_[block_count - 1]->AsGraphEntry();
+  for (intptr_t i = 0; i < graph_entry->start_env()->values().length(); i++) {
+    Value* val = graph_entry->start_env()->values()[i];
+    if (val->IsUse()) {
+      const intptr_t vreg = val->AsUse()->definition()->ssa_temp_index();
+      kill_[0]->Add(vreg);

[Kevin Millikin (Google), 2012/07/26 09:29:08]

It probably doesn't make a big difference to anything, but I don't understand
why the incoming parameters are not live at the graph entry.

[Vyacheslav Egorov (Google), 2012/07/26 11:33:53]

It does not change anything. I just choose to define them at graph entry.

+      live_in_[0]->Remove(vreg);
+    }
+  }
+
   // Update initial live_in sets to match live_out sets. Has to be
   // done in a separate path because of backwards branches.
   for (intptr_t i = 0; i < block_count; i++) {
@@ -396,6 +407,31 @@ void FlowGraphAllocator::BuildLiveRanges() {
 
     ConnectIncomingPhiMoves(block);
   }
+
+  // Process incomming parameters.

[srdjan, 2012/07/26 00:33:56]

ditto

[Vyacheslav Egorov (Google), 2012/07/26 11:33:53]

Done.

+  GraphEntryInstr* graph_entry = postorder_[block_count - 1]->AsGraphEntry();
+  for (intptr_t i = 0; i < graph_entry->start_env()->values().length(); i++) {
+    Value* val = graph_entry->start_env()->values()[i];
+    if (val->IsUse()) {
+      ParameterInstr* param = val->AsUse()->definition()->AsParameter();
+
+      LiveRange* range = GetLiveRange(param->ssa_temp_index());
+      range->AddUseInterval(graph_entry->start_pos(), graph_entry->end_pos());
+      range->DefineAt(graph_entry->start_pos());
+      range->set_assigned_location(Location::StackSlot(param->index()));
+
+      range->finger()->Initialize(range);
+      UsePosition* use = range->finger()->FirstRegisterBeneficialUse(
+          graph_entry->start_pos());
+      if (use != NULL) {
+        LiveRange* tail = SplitBetween(range,
+                                       graph_entry->start_pos(),
+                                       use->pos());
+        AddToUnallocated(tail);
+      }
+      ConvertAllUses(range);
+    }
+  }
 }
 
 //
@@ -547,6 +583,14 @@ void FlowGraphAllocator::ProcessOneInstruction(BlockEntryInstr* block,
     builder_->Bailout("ssa allocator: number of input locations mismatch");
   }
 
+  // Normalize same-as-first-input output if input is specified as
+  // fixed register.
+  if (locs->out().IsUnallocated() &&
+      (locs->out().policy() == Location::kSameAsFirstInput) &&
+      (locs->in(0).IsRegister())) {
+    locs->set_out(locs->in(0));
+  }
+
   const bool output_same_as_first_input =
       locs->out().IsUnallocated() &&
       (locs->out().policy() == Location::kSameAsFirstInput);
@@ -1095,9 +1139,9 @@ intptr_t FlowGraphAllocator::AllocateSpillSlotFor(LiveRange* range) {
 
 void FlowGraphAllocator::Spill(LiveRange* range) {
   const intptr_t spill_index = AllocateSpillSlotFor(range);
-  ASSERT(spill_slots_[spill_index] < range->Start());
+  ASSERT(spill_slots_[spill_index] <= range->Start());
   spill_slots_[spill_index] = range->End();
-  range->set_assigned_location(Location::SpillSlot(spill_index));
+  range->set_assigned_location(Location::StackSlot(spill_index));
   ConvertAllUses(range);
 }
 
@@ -1575,15 +1619,6 @@ void FlowGraphAllocator::ResolveControlFlow() {
 
 
 void FlowGraphAllocator::AllocateRegisters() {
-  GraphEntryInstr* entry = block_order_[0]->AsGraphEntry();
-  ASSERT(entry != NULL);
-
-  for (intptr_t i = 0; i < entry->start_env()->values().length(); i++) {
-    if (entry->start_env()->values()[i]->IsUse()) {
-      builder_->Bailout("ssa allocator: unsupported start environment");
-    }
-  }
-
   AnalyzeLiveness();
 
   BuildLiveRanges();
@@ -1600,6 +1635,10 @@ void FlowGraphAllocator::AllocateRegisters() {
 
   ResolveControlFlow();
 
+  GraphEntryInstr* entry = block_order_[0]->AsGraphEntry();
+  ASSERT(entry != NULL);
+  entry->set_spill_slot_count(spill_slots_.length());
+
   if (FLAG_trace_ssa_allocator) {
     OS::Print("-- ir after allocation -------------------------\n");
     FlowGraphPrinter printer(Function::Handle(), block_order_, true);