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.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@218461 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/AST/MicrosoftMangle.cpp b/lib/AST/MicrosoftMangle.cpp
index ba057e2084f76e923cd249c59ceba67b9919a983..d5566e70ca3629249a1f4be9adca0c7f9ed86fe0 100644 (file)
--- a/lib/AST/MicrosoftMangle.cpp
+++ b/lib/AST/MicrosoftMangle.cpp
@@ -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::mangleOperatorName(OverloadedOperatorKind OO,
 
 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::mangleTemplateInstantiationName(
 
   // Templates have their own context for back references.
   ArgBackRefMap OuterArgsContext;
-  BackRefMap OuterTemplateContext;
+  BackRefVec OuterTemplateContext;
   NameBackReferences.swap(OuterTemplateContext);
   TypeBackReferences.swap(OuterArgsContext);