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, 3 insertions, 1 deletions

diff --git a/llvm/utils/TableGen/CodeGenInstruction.cpp b/llvm/utils/TableGen/CodeGenInstruction.cpp
index 366e8ec7fac..bd26beb3567 100644
--- a/llvm/utils/TableGen/CodeGenInstruction.cpp
+++ b/llvm/utils/TableGen/CodeGenInstruction.cpp
@@ -49,7 +49,9 @@ CGIOperandList::CGIOperandList(Record *R) : TheDef(R) {
 
   unsigned MIOperandNo = 0;
   std::set<std::string> OperandNames;
-  for (unsigned i = 0, e = InDI->getNumArgs()+OutDI->getNumArgs(); i != e; ++i){
+  unsigned e = InDI->getNumArgs() + OutDI->getNumArgs();
+  OperandList.reserve(e);
+  for (unsigned i = 0; i != e; ++i){
     Init *ArgInit;
     std::string ArgName;
     if (i < NumDefs) {