[csa] fix variable merge for switch default label

Bug: 
Change-Id: I52e757aa2de951ff40660545472321c7dec84241
Reviewed-on: https://chromium-review.googlesource.com/632156Reviewed-by: Daniel Clifford <danno@chromium.org>
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48167}

src/compiler/code-assembler.cc

@@ -1208,8 +1208,8 @@ void CodeAssembler::Switch(Node* index, Label* default_label,
   for (size_t i = 0; i < case_count; ++i) {
     labels[i] = case_labels[i]->label_;
     case_labels[i]->MergeVariables();
-    default_label->MergeVariables();
   }
+  default_label->MergeVariables();
   return raw_assembler()->Switch(index, default_label->label_, case_values,
                                  labels, case_count);
 }

src/compiler/instruction-selector.cc

@@ -2473,6 +2473,7 @@ void InstructionSelector::VisitOsrValue(Node* node) {
 
 void InstructionSelector::VisitPhi(Node* node) {
   const int input_count = node->op()->ValueInputCount();
+  DCHECK_EQ(input_count, current_block_->PredecessorCount());
   PhiInstruction* phi = new (instruction_zone())
       PhiInstruction(instruction_zone(), GetVirtualRegister(node),
                      static_cast<size_t>(input_count));

test/cctest/compiler/test-code-assembler.cc

@@ -4,6 +4,8 @@
 
 #include "src/code-factory.h"
 #include "src/compiler/code-assembler.h"
+#include "src/compiler/node-properties.h"
+#include "src/compiler/opcodes.h"
 #include "src/isolate.h"
 #include "src/objects-inl.h"
 #include "test/cctest/compiler/code-assembler-tester.h"
@@ -309,18 +311,23 @@ TEST(VariableMergeSwitch) {
   Label l1(&m), l2(&m), default_label(&m);
   Label* labels[] = {&l1, &l2};
   int32_t values[] = {1, 2};
-  Node* temp = m.Int32Constant(0);
-  var1.Bind(temp);
+  Node* temp1 = m.Int32Constant(0);
+  var1.Bind(temp1);
   m.Switch(m.Int32Constant(2), &default_label, values, labels, 2);
   m.Bind(&l1);
-  DCHECK_EQ(temp, var1.value());
-  m.Return(temp);
+  CHECK_EQ(temp1, var1.value());
+  m.Return(temp1);
   m.Bind(&l2);
-  DCHECK_EQ(temp, var1.value());
-  m.Return(temp);
+  CHECK_EQ(temp1, var1.value());
+  Node* temp2 = m.Int32Constant(7);
+  var1.Bind(temp2);
+  m.Goto(&default_label);
   m.Bind(&default_label);
-  DCHECK_EQ(temp, var1.value());
-  m.Return(temp);
+  CHECK_EQ(IrOpcode::kPhi, var1.value()->opcode());
+  CHECK_EQ(2, var1.value()->op()->ValueInputCount());
+  CHECK_EQ(temp1, NodeProperties::GetValueInput(var1.value(), 0));
+  CHECK_EQ(temp2, NodeProperties::GetValueInput(var1.value(), 1));
+  m.Return(temp1);
 }
 
 TEST(SplitEdgeBranchMerge) {