Minor performance tweaks to llvm-tblgen (and a few that might be a good idea)

Summary:
This patch adds a reserve call to an expensive function
(`llvm::LoadIntrinsics`), and may fix a few other low hanging
performance fruit (I've put them in comments for now, so we can
discuss).

**Motivation:**

As I'm sure other developers do, when I build LLVM, I build the entire
project with the same config (`Debug`, `MinSizeRel`, `Release`, or
`RelWithDebInfo`). However, the `Debug` config also builds llvm-tblgen
in `Debug` mode. Later build steps that run llvm-tblgen then can
actually be the slowest steps in the entire build. Nobody likes slow
builds.

Reviewers: rnk, dblaikie

Differential Revision: http://reviews.llvm.org/D16832

Patch by Alexander G. Riccio

llvm-svn: 259683

1 files changed, 2 insertions, 1 deletions

diff --git a/llvm/utils/TableGen/CodeGenTarget.cpp b/llvm/utils/TableGen/CodeGenTarget.cpp
index 7c2c601..66ba73c 100644
--- a/llvm/utils/TableGen/CodeGenTarget.cpp
+++ b/llvm/utils/TableGen/CodeGenTarget.cpp
@@ -441,6 +441,7 @@ std::vector<CodeGenIntrinsic> llvm::LoadIntrinsics(const RecordKeeper &RC,
   std::vector<Record*> I = RC.getAllDerivedDefinitions("Intrinsic");
 
   std::vector<CodeGenIntrinsic> Result;
+  Result.reserve(I.size());
 
   for (unsigned i = 0, e = I.size(); i != e; ++i) {
     bool isTarget = I[i]->getValueAsBit("isTarget");
@@ -448,7 +449,7 @@ std::vector<CodeGenIntrinsic> llvm::LoadIntrinsics(const RecordKeeper &RC,
       Result.push_back(CodeGenIntrinsic(I[i]));
   }
   std::sort(Result.begin(), Result.end(),
-            [](CodeGenIntrinsic LHS, CodeGenIntrinsic RHS) {
+            [](const CodeGenIntrinsic& LHS, const CodeGenIntrinsic& RHS) {
               return LHS.Name < RHS.Name;
             });
   return Result;