[Courgette] Remove label trimming feature, which was used by ARM only.

Courgette's algorithm allow removal for underused labels. However, this
was only used by ARM, whose support is recently removed. This CL is a
follow-up to remove more dead code.

* Remove AssemblyProgram::TrimLabels()
* Remove LabelManager::RemoveUnderusedLabels() and usage in test.

Bug: 1012592
Change-Id: Ia50ee2ec9f90e35ce123463e06edc9bfb5a868af
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1987863Reviewed-by: Etienne Pierre-Doray <etiennep@chromium.org>
Commit-Queue: Samuel Huang <huangs@chromium.org>
Cr-Commit-Position: refs/heads/master@{#728682}

courgette/assembly_program.cc

@@ -67,20 +67,6 @@ void AssemblyProgram::PrecomputeLabels(RvaVisitor* abs32_visitor,
                                        RvaVisitor* rel32_visitor) {
   abs32_label_manager_.Read(abs32_visitor);
   rel32_label_manager_.Read(rel32_visitor);
-  // TrimLabels() should be called here if used. Previously this was used only
-  // for ARM binaries, but ARM support has been deprecated.
-}
-
-// Chosen empirically to give the best reduction in payload size for
-// an update from daisy_3701.98.0 to daisy_4206.0.0.
-const int AssemblyProgram::kLabelLowerLimit = 5;
-
-void AssemblyProgram::TrimLabels() {
-  int lower_limit = kLabelLowerLimit;
-
-  VLOG(1) << "TrimLabels: threshold " << lower_limit;
-
-  rel32_label_manager_.RemoveUnderusedLabels(lower_limit);
 }
 
 void AssemblyProgram::UnassignIndexes() {

courgette/assembly_program.h

@@ -55,10 +55,6 @@ class AssemblyProgram {
   // Traverses RVAs in |abs32_visitor| and |rel32_visitor| to precompute Labels.
   void PrecomputeLabels(RvaVisitor* abs32_visitor, RvaVisitor* rel32_visitor);
 
-  // Removes underused Labels. Thresholds used (0 = no trimming) is
-  // architecture-dependent.
-  void TrimLabels();
-
   void UnassignIndexes();
   void DefaultAssignIndexes();
   void AssignRemainingIndexes();

courgette/label_manager.cc

@@ -113,17 +113,6 @@ Label* LabelManager::Find(RVA rva) {
   return it == labels_.end() || it->rva_ != rva ? nullptr : &(*it);
 }
 
-void LabelManager::RemoveUnderusedLabels(int32_t count_threshold) {
-  if (count_threshold <= 0)
-    return;
-  labels_.erase(std::remove_if(labels_.begin(), labels_.end(),
-                               [count_threshold](const Label& label) {
-                                 return label.count_ < count_threshold;
-                               }),
-                labels_.end());
-  // Not shrinking |labels_|, since this may cause reallocation.
-}
-
 void LabelManager::UnassignIndexes() {
   for (Label& label : labels_)
     label.index_ = Label::kNoIndex;

courgette/label_manager_unittest.cc

@@ -155,14 +155,6 @@ TEST(LabelManagerTest, Basic) {
   EXPECT_EQ(nullptr, label_manager.Find(RVA(0x5F3759DF)));
   EXPECT_EQ(nullptr, label_manager.Find(RVA(0xFEEDFFF0)));
   EXPECT_EQ(nullptr, label_manager.Find(RVA(0xFFFFFFFF)));
-
-  // Remove Labels with |count_| < 2.
-  label_manager.RemoveUnderusedLabels(2);
-  static const std::pair<RVA, int32_t> kExpected2Raw[] = {
-      {0x04000010, 3}, {0x04000030, 2}, {0xFEEDF00D, 2}};
-  std::map<RVA, int32_t> expected2(std::begin(kExpected2Raw),
-                                   std::end(kExpected2Raw));
-  CheckLabelManagerContent(&label_manager, expected2);
 }
 
 TEST(LabelManagerTest, Single) {
@@ -324,8 +316,8 @@ TEST(LabelManagerTest, AssignRemainingIndexes) {
     {"....AC", "BDEFAC"},
     {"ED...C...B....A", "EDFGHCIJKBLMNOA"},
     // Forward fill and infill.
-    {"E..", "EBA"},  // Forward: "A"; in: "B".
-    {"Z....", "ZDABC"},  // Forward: "ABC"; in: "D".
+    {"E..", "EBA"},          // Forward: "A"; in: "B".
+    {"Z....", "ZDABC"},      // Forward: "ABC"; in: "D".
     {".E.....", "AEFGBCD"},  // Forward: "A", "FG"; in: "BCD".
     {"....C..", "ABFGCDE"},  // Forward: "AB", "DE"; in: "FG".
     {"...Z...", "ABCZDEF"},  // Forward: "ABC"; in: "DEF".
@@ -337,7 +329,7 @@ TEST(LabelManagerTest, AssignRemainingIndexes) {
     {"ANM..Z....L...T", "ANMXYZHIJKLQRST"},
     {"....G..Z...LAH", "CDEFGXYZIJKLAH"},
     // Forward fill and backward fill.
-    {"..ZA..", "XYZABC"},  // Forward: "BC"; backward: "XY".
+    {"..ZA..", "XYZABC"},    // Forward: "BC"; backward: "XY".
     {".....ZD", "ABCXYZD"},  // Forward: "ABC"; backward: "XY".
     {"DA.....", "DABCEFG"},  // Forward: "BC"; backward: "EFG".
     // Backward fill and infill.
@@ -346,7 +338,7 @@ TEST(LabelManagerTest, AssignRemainingIndexes) {
     // All.
     {".....ZED.", "ABCXYZEDF"},  // Forward: "ABC"; backward: "XY"; in: "F".
     {".....GD.", "ABCHFGDE"},  // Forward: "ABC", "E"; backward: "F"; in: "H".
-    {"..FE..GD..", "ABFECHGDIJ"}, // Forward: "AB"; backward: "IJ"; in: "CH".
+    {"..FE..GD..", "ABFECHGDIJ"},  // Forward: "AB"; backward: "IJ"; in: "CH".
   };
   for (const auto& test_case : kTestCases) {
     TestLabelManager label_manager;