[turbofan] Renamed tracing flags for TurboFan reducers and graph trimmer

Added trace printout for replacements in Turbofan reducers.
Renamed graph trimmer trace flag to avoid confusion.

Review-Url: https://codereview.chromium.org/2123283006
Cr-Commit-Position: refs/heads/master@{#37663}

src/compiler/graph-reducer.cc

@@ -168,6 +168,10 @@ void GraphReducer::Replace(Node* node, Node* replacement) {
 
 
 void GraphReducer::Replace(Node* node, Node* replacement, NodeId max_id) {
+  if (FLAG_trace_turbo_reduction) {
+    OFStream os(stdout);
+    os << "- Replacing " << *node << " with " << *replacement << std::endl;
+  }
   if (node == graph()->start()) graph()->SetStart(replacement);
   if (node == graph()->end()) graph()->SetEnd(replacement);
   if (replacement->id() <= max_id) {

src/compiler/graph-trimmer.cc

@@ -33,7 +33,7 @@ void GraphTrimmer::TrimGraph() {
     for (Edge edge : live->use_edges()) {
       Node* const user = edge.from();
       if (!IsLive(user)) {
-        if (FLAG_trace_turbo_reduction) {
+        if (FLAG_trace_turbo_trimming) {
           OFStream os(stdout);
           os << "DeadLink: " << *user << "(" << edge.index() << ") -> " << *live
              << std::endl;

src/flag-definitions.h

@@ -441,6 +441,7 @@ DEFINE_STRING(trace_turbo_cfg_file, NULL,
 DEFINE_BOOL(trace_turbo_types, true, "trace TurboFan's types")
 DEFINE_BOOL(trace_turbo_scheduler, false, "trace TurboFan's scheduler")
 DEFINE_BOOL(trace_turbo_reduction, false, "trace TurboFan's various reducers")
+DEFINE_BOOL(trace_turbo_trimming, false, "trace TurboFan's graph trimmer")
 DEFINE_BOOL(trace_turbo_jt, false, "trace TurboFan's jump threading")
 DEFINE_BOOL(trace_turbo_ceq, false, "trace TurboFan's control equivalence")
 DEFINE_BOOL(turbo_asm, true, "enable TurboFan for asm.js code")