[Courgette] Using LabelManager to reduce Courgette-apply peak RAM by 25%.

courgette/disassembler_win32_x64.cc

Index: courgette/disassembler_win32_x64.cc
diff --git a/courgette/disassembler_win32_x64.cc b/courgette/disassembler_win32_x64.cc
index ffa6c36a7aade5f0d7954149fc11bc667b91543c..2db35a39d8a103f8f9fa75b6ddf403e7af6f7edc 100644
--- a/courgette/disassembler_win32_x64.cc
+++ b/courgette/disassembler_win32_x64.cc
@@ -252,6 +252,9 @@ bool DisassemblerWin32X64::Disassemble(AssemblyProgram* target) {
 
   ParseRel32RelocsFromSections();
 
+  PrecomputeLabels(target);
+  RemoveUnusedRel32Locations(target);
+
   if (!ParseFile(target))
     return false;
 
@@ -357,6 +360,26 @@ std::string DisassemblerWin32X64::SectionName(const Section* section) {
   return name;
 }
 
+RvaVisitor* DisassemblerWin32X64::CreateAbs32TargetRvaVisitor() {
+  return new RvaVisitor_Abs32(abs32_locations_, *this);
+}
+
+RvaVisitor* DisassemblerWin32X64::CreateRel32TargetRvaVisitor() {
+  return new RvaVisitor_Rel32(rel32_locations_, *this);
+}
+
+void DisassemblerWin32X64::RemoveUnusedRel32Locations(
+    AssemblyProgram* program) {
+  auto cond = [this, program](RVA rva) -> bool {
+    // + 4 since offset is relative to start of next instruction.
+    RVA target_rva = rva + 4 + Read32LittleEndian(RVAToPointer(rva));
+    return program->FindRel32Label(target_rva) == nullptr;
+  };
+  rel32_locations_.erase(
+      std::remove_if(rel32_locations_.begin(), rel32_locations_.end(), cond),
+      rel32_locations_.end());
+}
+
 CheckBool DisassemblerWin32X64::ParseFile(AssemblyProgram* program) {
   // Walk all the bytes in the file, whether or not in a section.
   FileOffset file_offset = 0;
@@ -525,12 +548,13 @@ void DisassemblerWin32X64::ParseRel32RelocsFromSection(const Section* section) {
       if (abs32_pos != abs32_locations_.end()) {
         if (*abs32_pos < rel32_rva + 4) {
           // Beginning of abs32 reloc is before end of rel32 reloc so they
-          // overlap.  Skip four bytes past the abs32 reloc.
+          // overlap. Skip four bytes past the abs32 reloc.
           p += (*abs32_pos + 4) - current_rva;
           continue;
         }
       }
 
+      // + 4 since offset is relative to start of next instruction.
       RVA target_rva = rel32_rva + 4 + Read32LittleEndian(rel32);
       // To be valid, rel32 target must be within image, and within this
       // section.
@@ -614,7 +638,9 @@ CheckBool DisassemblerWin32X64::ParseFileRegion(const Section* section,
       DCHECK_NE(kNoRVA, target_rva);
       // TODO(sra): target could be Label+offset.  It is not clear how to guess
       // which it might be.  We assume offset==0.
-      if (!program->EmitAbs64(program->FindOrMakeAbs32Label(target_rva)))
+      Label* label = program->FindAbs32Label(target_rva);
+      DCHECK(label);
+      if (!program->EmitAbs64(label))
         return false;
       p += 8;
       continue;
@@ -624,8 +650,11 @@ CheckBool DisassemblerWin32X64::ParseFileRegion(const Section* section,
       ++rel32_pos;
 
     if (rel32_pos != rel32_locations_.end() && *rel32_pos == current_rva) {
+      // + 4 since offset is relative to start of next instruction.
       RVA target_rva = current_rva + 4 + Read32LittleEndian(p);
-      if (!program->EmitRel32(program->FindOrMakeRel32Label(target_rva)))
+      Label* label = program->FindRel32Label(target_rva);
+      DCHECK(label);
+      if (!program->EmitRel32(label))
         return false;
       p += 4;
       continue;