[NFC] [DwarfEHPrepare] Add additional stats for EH

[modimo]

Summary

Stats added:

1. NumCleanupLandingPadsUnreachable: how many cleanup landing pads were optimized as unreachable
2. NumCleanupLandingPadsRemaining: how many cleanup landing pads remain
3. NumNoUnwind: Number of functions with nounwind attribute
4. NumUnwind: Number of functions with unwind attribute

DwarfEHPrepare is always run a single time as part of TargetPassConfig::addISelPasses() which makes it an ideal place near the end of the pipeline to record this information.

Example output from clang built with exceptions cumulative during thinLTO backend (NumCleanupLandingPadsUnreachable was not incremented):

"dwarfehprepare.NumCleanupLandingPadsRemaining": 123660,
"dwarfehprepare.NumNoUnwind": 323836,
"dwarfehprepare.NumUnwind": 472893,

[wenlei]

llvm/lib/CodeGen/DwarfEHPrepare.cpp

45

The path leading to InsertUnwindResumeCalls is unconditional for all functions. So this is essentially a total function count. All stats have flat structure, so, 1) we don't add a total function count stats for each pass; 2) The description of each stats need to be informative about what a particular pass did, "Number of functions processed" is too general. If you want to compare against NumNoUnwind, perhaps you could add NunUnwind.

46

• " in program" is implicit for all stats.
• This seems to be the count before pruning unreachable LP, but it's unclear from the name. Suggest name the two counter as something like "Number of cleanup landing pads removed", "Number of cleanup landing pads remained".

[modimo]

Review comments

[wenlei]

lgtm, thanks.

[modimo]

Clang-format

llvm/lib/CodeGen/DwarfEHPrepare.cpp

 #include "llvm/Transforms/Utils/Local.h"
 #include <cstddef>
 
 using namespace llvm;
 
 #define DEBUG_TYPE "dwarfehprepare"
 
 STATISTIC(NumResumesLowered, "Number of resume calls lowered");
+STATISTIC(NumCleanupLandingPadsUnreachable,
+          "Number of cleanup landing pads found unreachable");
+STATISTIC(NumCleanupLandingPadsRemaining,
+          "Number of cleanup landing pads remaining");
+STATISTIC(NumNoUnwind, "Number of functions with nounwind");
+STATISTIC(NumUnwind, "Number of functions with unwind");
 
 namespace {
 
 class DwarfEHPrepare {
   CodeGenOpt::Level OptLevel;
 
   // RewindFunction - _Unwind_Resume or the target equivalent.
   FunctionCallee &RewindFunction;
size_t DwarfEHPrepare::pruneUnreachableResumes(
   }
   Resumes.resize(ResumesLeft);
   return ResumesLeft;
 }
 
 bool DwarfEHPrepare::InsertUnwindResumeCalls() {
   SmallVector<ResumeInst *, 16> Resumes;
   SmallVector<LandingPadInst *, 16> CleanupLPads;
+  if (F.doesNotThrow())
+    NumNoUnwind++;
+  else
+    NumUnwind++;
   for (BasicBlock &BB : F) {
     if (auto *RI = dyn_cast<ResumeInst>(BB.getTerminator()))
       Resumes.push_back(RI);
     if (auto *LP = BB.getLandingPadInst())
       if (LP->isCleanup())
         CleanupLPads.push_back(LP);
   }
 
+  NumCleanupLandingPadsRemaining += CleanupLPads.size();
+
   if (Resumes.empty())
     return false;
 
   // Check the personality, don't do anything if it's scope-based.
   EHPersonality Pers = classifyEHPersonality(F.getPersonalityFn());
   if (isScopedEHPersonality(Pers))
     return false;
 
   LLVMContext &Ctx = F.getContext();
 
   size_t ResumesLeft = Resumes.size();
-  if (OptLevel != CodeGenOpt::None)
+  if (OptLevel != CodeGenOpt::None) {
     ResumesLeft = pruneUnreachableResumes(Resumes, CleanupLPads);
+#if LLVM_ENABLE_STATS
+    unsigned NumRemainingLPs = 0;
+    for (BasicBlock &BB : F) {
+      if (auto *LP = BB.getLandingPadInst())
+        if (LP->isCleanup())
+          NumRemainingLPs++;
+    }
+    NumCleanupLandingPadsUnreachable += CleanupLPads.size() - NumRemainingLPs;
+    NumCleanupLandingPadsRemaining -= CleanupLPads.size() - NumRemainingLPs;
+#endif
+  }
 
   if (ResumesLeft == 0)
     return true; // We pruned them all.
 
   // Find the rewind function if we didn't already.
   if (!RewindFunction) {
     FunctionType *FTy =
         FunctionType::get(Type::getVoidTy(Ctx), Type::getInt8PtrTy(Ctx), false);