r218461 - MS ABI: Avoid hashing back reference keys in mangler

[David Majnemer]

Author: majnemer
Date: Thu Sep 25 14:43:56 2014
New Revision: 218461

URL: http://llvm.org/viewvc/llvm-project?rev=218461&view=rev
Log:
MS ABI: Avoid hashing back reference keys in mangler

This patch replaces the back reference StringMap from the MS mangler
with a SmallVector of strings. My previous patches reduced the number of
hashes involved in back reference lookups, this one removes them
completely. The back reference map contains at most 10 entries, which
are likely to be of varying sizes and different initial subsequences,
and which can easily became huge (due to templates and namespaces).

The solution presented is the simplest possible one. Nevertheless, it's
enough to reduce compilation times for a particular test case from 11.1s
to 9s, versus 8.58s for the Itanium ABI. Possible further improvements
include using a sorted vector (carefully to not introduce an extra
comparison), storing the string contents in a common arena, and/or keep
the string storage in the context for reuse.

Patch by Agustín Bergé.

Modified:
    cfe/trunk/lib/AST/MicrosoftMangle.cpp

Modified: cfe/trunk/lib/AST/MicrosoftMangle.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/AST/MicrosoftMangle.cpp?rev=218461&r1=218460&r2=218461&view=diff
==============================================================================
--- cfe/trunk/lib/AST/MicrosoftMangle.cpp (original)
+++ cfe/trunk/lib/AST/MicrosoftMangle.cpp Thu Sep 25 14:43:56 2014
@@ -27,7 +27,6 @@
 #include "clang/Basic/DiagnosticOptions.h"
 #include "clang/Basic/TargetInfo.h"
 #include "llvm/ADT/StringExtras.h"
-#include "llvm/ADT/StringMap.h"
 #include "llvm/Support/MathExtras.h"
 
 using namespace clang;
@@ -191,8 +190,8 @@ class MicrosoftCXXNameMangler {
   const NamedDecl *Structor;
   unsigned StructorType;
 
-  typedef llvm::StringMap<unsigned> BackRefMap;
-  BackRefMap NameBackReferences;
+  typedef llvm::SmallVector<std::string, 10> BackRefVec;
+  BackRefVec NameBackReferences;
 
   typedef llvm::DenseMap<void *, unsigned> ArgBackRefMap;
   ArgBackRefMap TypeBackReferences;
@@ -994,22 +993,14 @@ void MicrosoftCXXNameMangler::mangleOper
 
 void MicrosoftCXXNameMangler::mangleSourceName(StringRef Name) {
   // <source name> ::= <identifier> @
-  BackRefMap::iterator Found;
-  if (NameBackReferences.size() < 10) {
-    size_t Size = NameBackReferences.size();
-    bool Inserted;
-    std::tie(Found, Inserted) =
-        NameBackReferences.insert(std::make_pair(Name, Size));
-    if (Inserted)
-      Found = NameBackReferences.end();
-  } else {
-    Found = NameBackReferences.find(Name);
-  }
-
+  BackRefVec::iterator Found =
+      std::find(NameBackReferences.begin(), NameBackReferences.end(), Name);
   if (Found == NameBackReferences.end()) {
+    if (NameBackReferences.size() < 10)
+      NameBackReferences.push_back(Name);
     Out << Name << '@';
   } else {
-    Out << Found->second;
+    Out << (Found - NameBackReferences.begin());
   }
 }
 
@@ -1025,7 +1016,7 @@ void MicrosoftCXXNameMangler::mangleTemp
 
   // Templates have their own context for back references.
   ArgBackRefMap OuterArgsContext;
-  BackRefMap OuterTemplateContext;
+  BackRefVec OuterTemplateContext;
   NameBackReferences.swap(OuterTemplateContext);
   TypeBackReferences.swap(OuterArgsContext);