Introduce DebugInfoProbe. This is used to monitor how llvm optimizer is treating debugging information.

It generates output that lools like

8 times line number info lost by Scalar Replacement of Aggregates (SSAUp) 
1 times line number info lost by Simplify well-known library calls 
12 times variable info lost by Jump Threading



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@127381 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Analysis/LoopPass.cpp

@@ -14,8 +14,10 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Analysis/LoopPass.h"
+#include "llvm/DebugInfoProbe.h"
 #include "llvm/Assembly/PrintModulePass.h"
 #include "llvm/Support/Debug.h"
+#include "llvm/Support/ManagedStatic.h"
 #include "llvm/Support/Timer.h"
 using namespace llvm;
 
@@ -51,6 +53,20 @@ public:
 char PrintLoopPass::ID = 0;
 }
 
+//===----------------------------------------------------------------------===//
+// DebugInfoProbe
+
+static DebugInfoProbeInfo *TheDebugProbe;
+static void createDebugInfoProbe() {
+  if (TheDebugProbe) return;
+      
+  // Constructed the first time this is called. This guarantees that the 
+  // object will be constructed, if -enable-debug-info-probe is set, 
+  // before static globals, thus it will be destroyed before them.
+  static ManagedStatic<DebugInfoProbeInfo> DIP;
+  TheDebugProbe = &*DIP;
+}
+
 //===----------------------------------------------------------------------===//
 // LPPassManager
 //
@@ -223,6 +239,7 @@ void LPPassManager::getAnalysisUsage(AnalysisUsage &Info) const {
 bool LPPassManager::runOnFunction(Function &F) {
   LI = &getAnalysis<LoopInfo>();
   bool Changed = false;
+  createDebugInfoProbe();
 
   // Collect inherited analysis from Module level pass manager.
   populateInheritedAnalysis(TPM->activeStack);
@@ -254,19 +271,21 @@ bool LPPassManager::runOnFunction(Function &F) {
     // Run all passes on the current Loop.
     for (unsigned Index = 0; Index < getNumContainedPasses(); ++Index) {  
       LoopPass *P = getContainedPass(Index);
-
       dumpPassInfo(P, EXECUTION_MSG, ON_LOOP_MSG,
                    CurrentLoop->getHeader()->getName());
       dumpRequiredSet(P);
 
       initializeAnalysisImpl(P);
-
+      if (TheDebugProbe)
+        TheDebugProbe->initialize(P, F);
       {
         PassManagerPrettyStackEntry X(P, *CurrentLoop->getHeader());
         TimeRegion PassTimer(getPassTimer(P));
 
         Changed |= P->runOnLoop(CurrentLoop, *this);
       }
+      if (TheDebugProbe)
+        TheDebugProbe->finalize(P, F);
 
       if (Changed)
         dumpPassInfo(P, MODIFICATION_MSG, ON_LOOP_MSG,