ftime-trace: Trace loop passes

[russell.gallop]

Summary

These can take a significant amount of time in some builds.

Suggested by Andrea Di Biagio.

[anton-afanasyev]

LGTM, thanks.

llvm/lib/Analysis/LoopPass.cpp

 #include "llvm/IR/Dominators.h"
 #include "llvm/IR/IRPrintingPasses.h"
 #include "llvm/IR/LLVMContext.h"
 #include "llvm/IR/OptBisect.h"
 #include "llvm/IR/PassManager.h"
 #include "llvm/IR/PassTimingInfo.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/Timer.h"
+#include "llvm/Support/TimeProfiler.h"
 #include "llvm/Support/raw_ostream.h"
 using namespace llvm;
 
 #define DEBUG_TYPE "loop-pass-manager"
 
 namespace {
 
 /// PrintLoopPass - Print a Function corresponding to a Loop.
#endif
   while (!LQ.empty()) {
     CurrentLoopDeleted = false;
     CurrentLoop = LQ.back();
 
     // Run all passes on the current Loop.
     for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {
       LoopPass *P = getContainedPass(Index);
 
+      llvm::TimeTraceScope LoopPassScope("RunLoopPass", P->getPassName());
+
       dumpPassInfo(P, EXECUTION_MSG, ON_LOOP_MSG,
                    CurrentLoop->getHeader()->getName());
       dumpRequiredSet(P);
 
       initializeAnalysisImpl(P);
 
       bool LocalChanged = false;
       {