Revise implementation of case-insensitive command names

Store both the as-written and lower-case command names and use
the latter to avoid case-insensitive string comparisons.

With this I obtain 2-6% speed increase (on Windows) for the configure
step with no significant changes in memory usage.  A case-insensitive
comparison is a lot slower than just calling `==` because the operator
will use things like memcmp, so prefer the latter.

The `cmSystemTools::LowerCase` function allocates a new string each time
it is called, so before this change we were allocating in:

* cmMakefile::Configure two times for each function
  (to look for `cmake_minimum_required` and `project`)
* cmMakefile::ExecuteCommand twice by function by calling
  cmState::GetCommand and copying the name

Now we are only allocating once by function instead of four.

1 files changed, 7 insertions, 3 deletions

diff --git a/Source/cmState.cxx b/Source/cmState.cxx
index a93fb11..a57be4d 100644
--- a/Source/cmState.cxx
+++ b/Source/cmState.cxx
@@ -462,13 +462,17 @@ void cmState::AddScriptedCommand(std::string const& name, cmCommand* command)
 
 cmCommand* cmState::GetCommand(std::string const& name) const
 {
-  std::string sName = cmSystemTools::LowerCase(name);
+  return GetCommandByExactName(cmSystemTools::LowerCase(name));
+}
+
+cmCommand* cmState::GetCommandByExactName(std::string const& name) const
+{
   std::map<std::string, cmCommand*>::const_iterator pos;
-  pos = this->ScriptedCommands.find(sName);
+  pos = this->ScriptedCommands.find(name);
   if (pos != this->ScriptedCommands.end()) {
     return pos->second;
   }
-  pos = this->BuiltinCommands.find(sName);
+  pos = this->BuiltinCommands.find(name);
   if (pos != this->BuiltinCommands.end()) {
     return pos->second;
   }