Proof of Concept: Allow ORE.emit to take a closure to delay building the remark object

[anemet]

Summary

In the lambda we are now returning the remark by value so we need to preserve
its type in the insertion operator. This requires making the insertion
operator generic.

I've also converted a few cases to use the new API. It seems to work pretty
well. See the LoopUnroller for a slightly more interesting case.

[anemet]

Implement DiagHandler::isAnyRemarkEnabled(void)

[anemet]

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[anemet]

This was committed a while ago.

include/llvm/Analysis/OptimizationDiagnosticInfo.h

OptimizationRemarkEmitter &operator=(OptimizationRemarkEmitter &&RHS) {
     BFI = RHS.BFI;
     return *this;
   }
 
   /// Handle invalidation events in the new pass manager.
   bool invalidate(Function &F, const PreservedAnalyses &PA,
                   FunctionAnalysisManager::Invalidator &Inv);
 
-  /// \brief Output the remark via the diagnostic handler and to the
-  /// optimization record file.
+  /// \brief Output the remark to the optimization record file.  Also send it to
+  /// the diagnostic handler if the remarks were requested for the pass.
   void emit(DiagnosticInfoOptimizationBase &OptDiag);
 
+  template <typename T>
+  void emit(T RemarkBuilder, decltype(RemarkBuilder()) * = nullptr) {
+    // Avoid building the remark unless we know there are at least *some*
+    // remarks enabled. We can't currently check whether remarks are requested
+    // for the calling pass since that requires actually building the remark.
+
+    // if (isAnyRemarkEnabled())
+    auto R = RemarkBuilder();
+    emit(R);
+  }
+
   /// \brief Whether we allow for extra compile-time budget to perform more
   /// analysis to produce fewer false positives.
   ///
   /// This is useful when reporting missed optimizations.  In this case we can
   /// use the extra analysis (1) to filter trivial false positives or (2) to
   /// provide more context so that non-trivial false positives can be quickly
   /// detected by the user.
   bool allowExtraAnalysis() const {

include/llvm/IR/DiagnosticInfo.h

public:
   DiagnosticInfoOptimizationBase(enum DiagnosticKind Kind,
                                  enum DiagnosticSeverity Severity,
                                  const char *PassName, StringRef RemarkName,
                                  const Function &Fn,
                                  const DiagnosticLocation &Loc)
       : DiagnosticInfoWithLocationBase(Kind, Severity, Fn, Loc),
         PassName(PassName), RemarkName(RemarkName) {}
 
-  DiagnosticInfoOptimizationBase &operator<<(StringRef S);
-  DiagnosticInfoOptimizationBase &operator<<(Argument A);
-  DiagnosticInfoOptimizationBase &operator<<(setIsVerbose V);
-  DiagnosticInfoOptimizationBase &operator<<(setExtraArgs EA);
+  void insert(StringRef S);
+  void insert(Argument A);
+  void insert(setIsVerbose V);
+  void insert(setExtraArgs EA);
 
   /// \see DiagnosticInfo::print.
   void print(DiagnosticPrinter &DP) const override;
 
   /// Return true if this optimization remark is enabled by one of
   /// of the LLVM command line flags (-pass-remarks, -pass-remarks-missed,
   /// or -pass-remarks-analysis). Note that this only handles the LLVM
   /// flags. We cannot access Clang flags from here (they are handled
protected:
   /// \brief If positive, the index of the first argument that only appear in
   /// the optimization records and not in the remark printed in the compiler
   /// output.
   int FirstExtraArgIndex = -1;
 
   friend struct yaml::MappingTraits<DiagnosticInfoOptimizationBase *>;
 };
 
+/// Allow the insertion operator to return the actual remark type rather than a
+/// common base class.  This allows returning the result of the insertion
+/// directly by value, e.g. return OptimizationRemarkAnalysis(...) << "blah".
+template <class RemarkT>
+RemarkT &
+operator<<(RemarkT &R,
+           typename std::enable_if<
+               std::is_base_of<DiagnosticInfoOptimizationBase, RemarkT>::value,
+               StringRef>::type S) {
+  R.insert(S);
+  return R;
+}
+
+/// Also allow r-value for the remark to allow insertion into a
+/// temporarily-constructed remark.
+template <class RemarkT>
+RemarkT &
+operator<<(RemarkT &&R,
+           typename std::enable_if<
+               std::is_base_of<DiagnosticInfoOptimizationBase, RemarkT>::value,
+               StringRef>::type S) {
+  R.insert(S);
+  return R;
+}
+
+template <class RemarkT>
+RemarkT &
+operator<<(RemarkT &R,
+           typename std::enable_if<
+               std::is_base_of<DiagnosticInfoOptimizationBase, RemarkT>::value,
+               DiagnosticInfoOptimizationBase::Argument>::type A) {
+  R.insert(A);
+  return R;
+}
+
+template <class RemarkT>
+RemarkT &
+operator<<(RemarkT &&R,
+           typename std::enable_if<
+               std::is_base_of<DiagnosticInfoOptimizationBase, RemarkT>::value,
+               DiagnosticInfoOptimizationBase::Argument>::type A) {
+  R.insert(A);
+  return R;
+}
+
+template <class RemarkT>
+RemarkT &
+operator<<(RemarkT &R,
+           typename std::enable_if<
+               std::is_base_of<DiagnosticInfoOptimizationBase, RemarkT>::value,
+               DiagnosticInfoOptimizationBase::setIsVerbose>::type V) {
+  R.insert(V);
+  return R;
+}
+
+template <class RemarkT>
+RemarkT &
+operator<<(RemarkT &&R,
+           typename std::enable_if<
+               std::is_base_of<DiagnosticInfoOptimizationBase, RemarkT>::value,
+               DiagnosticInfoOptimizationBase::setIsVerbose>::type V) {
+  R.insert(V);
+  return R;
+}
+
+template <class RemarkT>
+RemarkT &
+operator<<(RemarkT &R,
+           typename std::enable_if<
+               std::is_base_of<DiagnosticInfoOptimizationBase, RemarkT>::value,
+               DiagnosticInfoOptimizationBase::setExtraArgs>::type EA) {
+  R.insert(EA);
+  return R;
+}
+
 /// \brief Common features for diagnostics dealing with optimization remarks
 /// that are used by IR passes.
 class DiagnosticInfoIROptimization : public DiagnosticInfoOptimizationBase {
 public:
   /// \p PassName is the name of the pass emitting this diagnostic. \p
   /// RemarkName is a textual identifier for the remark (single-word,
   /// camel-case). \p Fn is the function where the diagnostic is being emitted.
   /// \p Loc is the location information to use in the diagnostic. If line table

lib/IR/DiagnosticInfo.cpp

void DiagnosticInfoUnsupported::print(DiagnosticPrinter &DP) const {
   OS.flush();
   DP << Str;
 }
 
 void DiagnosticInfoISelFallback::print(DiagnosticPrinter &DP) const {
   DP << "Instruction selection used fallback path for " << getFunction();
 }
 
-DiagnosticInfoOptimizationBase &DiagnosticInfoOptimizationBase::
-operator<<(StringRef S) {
+void DiagnosticInfoOptimizationBase::insert(StringRef S) {
   Args.emplace_back(S);
-  return *this;
 }
 
-DiagnosticInfoOptimizationBase &DiagnosticInfoOptimizationBase::
-operator<<(Argument A) {
+void DiagnosticInfoOptimizationBase::insert(Argument A) {
   Args.push_back(std::move(A));
-  return *this;
 }
 
-DiagnosticInfoOptimizationBase &DiagnosticInfoOptimizationBase::
-operator<<(setIsVerbose V) {
+void DiagnosticInfoOptimizationBase::insert(setIsVerbose V) {
   IsVerbose = true;
-  return *this;
 }
 
-DiagnosticInfoOptimizationBase &DiagnosticInfoOptimizationBase::
-operator<<(setExtraArgs EA) {
+void DiagnosticInfoOptimizationBase::insert(setExtraArgs EA) {
   FirstExtraArgIndex = Args.size();
-  return *this;
 }
 
 std::string DiagnosticInfoOptimizationBase::getMsg() const {
   std::string Str;
   raw_string_ostream OS(Str);
   for (const DiagnosticInfoOptimizationBase::Argument &Arg :
        make_range(Args.begin(), FirstExtraArgIndex == -1
                                     ? Args.end()
                                     : Args.begin() + FirstExtraArgIndex))
     OS << Arg.Val;
   return OS.str();
 }

lib/Transforms/IPO/Inliner.cpp

if (IC.isAlways()) {
     DEBUG(dbgs() << "    Inlining: cost=always"
                  << ", Call: " << *CS.getInstruction() << "\n");
     return IC;
   }
 
   if (IC.isNever()) {
     DEBUG(dbgs() << "    NOT Inlining: cost=never"
                  << ", Call: " << *CS.getInstruction() << "\n");
-    ORE.emit(OptimizationRemarkMissed(DEBUG_TYPE, "NeverInline", Call)
+    ORE.emit([&]() {
+      return OptimizationRemarkMissed(DEBUG_TYPE, "NeverInline", Call)
              << NV("Callee", Callee) << " not inlined into "
              << NV("Caller", Caller)
-             << " because it should never be inlined (cost=never)");
+             << " because it should never be inlined (cost=never)";
+    });
     return None;
   }
 
   if (!IC) {
     DEBUG(dbgs() << "    NOT Inlining: cost=" << IC.getCost()
                  << ", thres=" << IC.getThreshold()
                  << ", Call: " << *CS.getInstruction() << "\n");
-    ORE.emit(OptimizationRemarkMissed(DEBUG_TYPE, "TooCostly", Call)
+    ORE.emit([&]() {
+      return OptimizationRemarkMissed(DEBUG_TYPE, "TooCostly", Call)
              << NV("Callee", Callee) << " not inlined into "
              << NV("Caller", Caller) << " because too costly to inline (cost="
              << NV("Cost", IC.getCost())
-             << ", threshold=" << NV("Threshold", IC.getThreshold()) << ")");
+             << ", threshold=" << NV("Threshold", IC.getThreshold()) << ")";
+    });
     return None;
   }
 
   int TotalSecondaryCost = 0;
   if (shouldBeDeferred(Caller, CS, IC, TotalSecondaryCost, GetInlineCost)) {
     DEBUG(dbgs() << "    NOT Inlining: " << *CS.getInstruction()
                  << " Cost = " << IC.getCost()
                  << ", outer Cost = " << TotalSecondaryCost << '\n');
for (unsigned CSi = 0; CSi != CallSites.size(); ++CSi) {
         }
         ++NumInlined;
 
         if (OIC->isAlways())
           ORE.emit(OptimizationRemark(DEBUG_TYPE, "AlwaysInline", DLoc, Block)
                    << NV("Callee", Callee) << " inlined into "
                    << NV("Caller", Caller) << " with cost=always");
         else
-          ORE.emit(OptimizationRemark(DEBUG_TYPE, "Inlined", DLoc, Block)
+          ORE.emit([&]() {
+            return OptimizationRemark(DEBUG_TYPE, "Inlined", DLoc, Block)
                    << NV("Callee", Callee) << " inlined into "
                    << NV("Caller", Caller)
                    << " with cost=" << NV("Cost", OIC->getCost())
                    << " (threshold=" << NV("Threshold", OIC->getThreshold())
-                   << ")");
+                   << ")";
+          });
 
         // If inlining this function gave us any new call sites, throw them
         // onto our worklist to process.  They are useful inline candidates.
         if (!InlineInfo.InlinedCalls.empty()) {
           // Create a new inline history entry for this, so that we remember
           // that these new callsites came about due to inlining Callee.
           int NewHistoryID = InlineHistory.size();
           InlineHistory.push_back(std::make_pair(Callee, InlineHistoryID));

lib/Transforms/Utils/LoopUnroll.cpp

bool llvm::UnrollLoop(Loop *L, unsigned Count, unsigned TripCount, bool Force,
   } else if (PeelCount) {
     DEBUG(dbgs() << "PEELING loop %" << Header->getName()
                  << " with iteration count " << PeelCount << "!\n");
     ORE->emit(OptimizationRemark(DEBUG_TYPE, "Peeled", L->getStartLoc(),
                                  L->getHeader())
               << " peeled loop by " << NV("PeelCount", PeelCount)
               << " iterations");
   } else {
+    auto DiagBuilder = [&]() {
       OptimizationRemark Diag(DEBUG_TYPE, "PartialUnrolled", L->getStartLoc(),
                               L->getHeader());
-    Diag << "unrolled loop by a factor of " << NV("UnrollCount", Count);
+      return Diag << "unrolled loop by a factor of "
+                  << NV("UnrollCount", Count);
+    };
 
     DEBUG(dbgs() << "UNROLLING loop %" << Header->getName()
           << " by " << Count);
     if (TripMultiple == 0 || BreakoutTrip != TripMultiple) {
       DEBUG(dbgs() << " with a breakout at trip " << BreakoutTrip);
-      ORE->emit(Diag << " with a breakout at trip "
-                     << NV("BreakoutTrip", BreakoutTrip));
+      ORE->emit([&]() {
+        return DiagBuilder() << " with a breakout at trip "
+                             << NV("BreakoutTrip", BreakoutTrip);
+      });
     } else if (TripMultiple != 1) {
       DEBUG(dbgs() << " with " << TripMultiple << " trips per branch");
-      ORE->emit(Diag << " with " << NV("TripMultiple", TripMultiple)
-                     << " trips per branch");
+      ORE->emit([&]() {
+        return DiagBuilder() << " with " << NV("TripMultiple", TripMultiple)
+                             << " trips per branch";
+      });
     } else if (RuntimeTripCount) {
       DEBUG(dbgs() << " with run-time trip count");
-      ORE->emit(Diag << " with run-time trip count");
+      ORE->emit([&]() { return DiagBuilder() << " with run-time trip count"; });
     }
     DEBUG(dbgs() << "!\n");
   }
 
   bool ContinueOnTrue = L->contains(BI->getSuccessor(0));
   BasicBlock *LoopExit = BI->getSuccessor(ContinueOnTrue);
 
   // For the first iteration of the loop, we should use the precloned values for

lib/Transforms/Vectorize/LoopVectorize.cpp

if (!AlwaysVectorize && getForce() != LoopVectorizeHints::FK_Enabled) {
       return false;
     }
 
     if (getIsVectorized() == 1) {
       DEBUG(dbgs() << "LV: Not vectorizing: Disabled/already vectorized.\n");
       // FIXME: Add interleave.disable metadata. This will allow
       // vectorize.disable to be used without disabling the pass and errors
       // to differentiate between disabled vectorization and a width of 1.
-      ORE.emit(OptimizationRemarkAnalysis(vectorizeAnalysisPassName(),
+      ORE.emit([&]() {
+        return OptimizationRemarkAnalysis(vectorizeAnalysisPassName(),
                                           "AllDisabled", L->getStartLoc(),
                                           L->getHeader())
                << "loop not vectorized: vectorization and interleaving are "
                   "explicitly disabled, or the loop has already been "
-                  "vectorized");
+                  "vectorized";
+      });
       return false;
     }
 
     return true;
   }
 
   /// Dumps all the hint information.
   void emitRemarkWithHints() const {