[CSA] Improve CSA debuggability

- Add BasicBlock::Print method for easier inspection in gdb
- Print detailed error message in InstructionSelector::VisitControl instead
  of just a check failure

Change-Id: Ice9d70567114f014b244c1b4e41e450900030994
Reviewed-on: https://chromium-review.googlesource.com/504388
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45295}

src/compiler/instruction-selector.cc

@@ -926,9 +926,14 @@ void InstructionSelector::VisitControl(BasicBlock* block) {
   if (block->SuccessorCount() > 1) {
     for (BasicBlock* const successor : block->successors()) {
       for (Node* const node : *successor) {
-        // If this CHECK fails, you might have specified merged variables
-        // for a label with only one predecessor.
-        CHECK(!IrOpcode::IsPhiOpcode(node->opcode()));
+        if (IrOpcode::IsPhiOpcode(node->opcode())) {
+          std::ostringstream str;
+          str << "You might have specified merged variables for a label with "
+              << "only one predecessor." << std::endl
+              << "# Current Block: " << *successor << std::endl
+              << "#          Node: " << *node;
+          FATAL(str.str().c_str());
+        }
       }
     }
   }

src/compiler/schedule.cc

@@ -4,8 +4,8 @@
 
 #include "src/compiler/schedule.h"
 
-#include "src/compiler/node.h"
 #include "src/compiler/node-properties.h"
+#include "src/compiler/node.h"
 #include "src/ostreams.h"
 
 namespace v8 {
@@ -96,6 +96,8 @@ BasicBlock* BasicBlock::GetCommonDominator(BasicBlock* b1, BasicBlock* b2) {
   return b1;
 }
 
+void BasicBlock::Print() { OFStream(stdout) << this; }
+
 std::ostream& operator<<(std::ostream& os, const BasicBlock& block) {
   os << "B" << block.id();
 #if DEBUG

src/compiler/schedule.h

@@ -65,6 +65,8 @@ class V8_EXPORT_PRIVATE BasicBlock final
   AssemblerDebugInfo debug_info() const { return debug_info_; }
 #endif  // DEBUG
 
+  void Print();
+
   // Predecessors.
   BasicBlockVector& predecessors() { return predecessors_; }
   const BasicBlockVector& predecessors() const { return predecessors_; }