Avoid extra back reference key lookup in msmangler

Avoid a second key lookup when the back reference key is going to be
inserted in the StringMap. The string lookups in the msmangler are the
main responsible for the huge overhead when compared to the itanium
mangler. This patch makes a small but noticeable improvement.

Reviewed by: rnk

Differential Revision: http://reviews.llvm.org/D4130

Patch by Agustín Bergé!

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@211813 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 17 insertions, 19 deletions

diff --git a/lib/AST/MicrosoftMangle.cpp b/lib/AST/MicrosoftMangle.cpp
index c2c8da95c6..141c2f6ef7 100644
--- a/lib/AST/MicrosoftMangle.cpp
+++ b/lib/AST/MicrosoftMangle.cpp
@@ -650,6 +650,7 @@ void MicrosoftCXXNameMangler::mangleUnqualifiedName(const NamedDecl *ND,
     // FIXME: Test alias template mangling with MSVC 2013.
     if (!isa<ClassTemplateDecl>(TD)) {
       mangleTemplateInstantiationName(TD, *TemplateArgs);
+      Out << '@';
       return;
     }
 
@@ -668,22 +669,13 @@ void MicrosoftCXXNameMangler::mangleUnqualifiedName(const NamedDecl *ND,
     // the mangled type name as a key to check the mangling of different types
     // for aliasing.
 
-    std::string TemplateMangling;
-    llvm::raw_string_ostream Stream(TemplateMangling);
+    llvm::SmallString<64> TemplateMangling;
+    llvm::raw_svector_ostream Stream(TemplateMangling);
     MicrosoftCXXNameMangler Extra(Context, Stream);
     Extra.mangleTemplateInstantiationName(TD, *TemplateArgs);
     Stream.flush();
 
-    BackRefMap::iterator Found = NameBackReferences.find(TemplateMangling);
-    if (Found == NameBackReferences.end()) {
-      Out << TemplateMangling;
-      if (NameBackReferences.size() < 10) {
-        size_t Size = NameBackReferences.size();
-        NameBackReferences[TemplateMangling] = Size;
-      }
-    } else {
-      Out << Found->second;
-    }
+    mangleSourceName(TemplateMangling);
     return;
   }
 
@@ -1002,13 +994,20 @@ void MicrosoftCXXNameMangler::mangleOperatorName(OverloadedOperatorKind OO,
 
 void MicrosoftCXXNameMangler::mangleSourceName(StringRef Name) {
   // <source name> ::= <identifier> @
-  BackRefMap::iterator Found = NameBackReferences.find(Name);
+  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);
+  }
+
   if (Found == NameBackReferences.end()) {
     Out << Name << '@';
-    if (NameBackReferences.size() < 10) {
-      size_t Size = NameBackReferences.size();
-      NameBackReferences[Name] = Size;
-    }
   } else {
     Out << Found->second;
   }
@@ -1104,10 +1103,9 @@ void MicrosoftCXXNameMangler::mangleExpression(const Expr *E) {
 
 void MicrosoftCXXNameMangler::mangleTemplateArgs(
     const TemplateDecl *TD, const TemplateArgumentList &TemplateArgs) {
-  // <template-args> ::= <template-arg>+ @
+  // <template-args> ::= <template-arg>+
   for (const TemplateArgument &TA : TemplateArgs.asArray())
     mangleTemplateArg(TD, TA);
-  Out << '@';
 }
 
 void MicrosoftCXXNameMangler::mangleTemplateArg(const TemplateDecl *TD,