[ORE] Add diagnostics hotness threshold

Summary:
Add an option to prevent diagnostics that do not meet a minimum hotness
threshold from being output. When generating optimization remarks for
large codebases with a ton of cold code paths, this option can be used
to limit the optimization remark output at a reasonable size. Discussion of
this change can be read here:
http://lists.llvm.org/pipermail/llvm-dev/2017-June/114377.html

Reviewers: anemet, davidxl, hfinkel

Reviewed By: anemet

Subscribers: qcolombet, javed.absar, fhahn, eraman, llvm-commits

Differential Revision: https://reviews.llvm.org/D34867

llvm-svn: 306912

4 files changed, 23 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/OptimizationDiagnosticInfo.cpp b/llvm/lib/Analysis/OptimizationDiagnosticInfo.cpp
index e1650040880..eb259fd7a38 100644
--- a/llvm/lib/Analysis/OptimizationDiagnosticInfo.cpp
+++ b/llvm/lib/Analysis/OptimizationDiagnosticInfo.cpp
@@ -155,6 +155,13 @@ void OptimizationRemarkEmitter::emit(
     DiagnosticInfoOptimizationBase &OptDiagBase) {
   auto &OptDiag = cast<DiagnosticInfoIROptimization>(OptDiagBase);
   computeHotness(OptDiag);
+  // If a diagnostic has a hotness value, then only emit it if its hotness
+  // meets the threshold.
+  if (OptDiag.getHotness() &&
+      *OptDiag.getHotness() <
+          F->getContext().getDiagnosticsHotnessThreshold()) {
+    return;
+  }
 
   yaml::Output *Out = F->getContext().getDiagnosticsOutputFile();
   if (Out) {
diff --git a/llvm/lib/CodeGen/MachineOptimizationRemarkEmitter.cpp b/llvm/lib/CodeGen/MachineOptimizationRemarkEmitter.cpp
index 957028fe039..73c3428a6e5 100644
--- a/llvm/lib/CodeGen/MachineOptimizationRemarkEmitter.cpp
+++ b/llvm/lib/CodeGen/MachineOptimizationRemarkEmitter.cpp
@@ -52,6 +52,14 @@ void MachineOptimizationRemarkEmitter::emit(
   computeHotness(OptDiag);
 
   LLVMContext &Ctx = MF.getFunction()->getContext();
+
+  // If a diagnostic has a hotness value, then only emit it if its hotness
+  // meets the threshold.
+  if (OptDiag.getHotness() &&
+      *OptDiag.getHotness() < Ctx.getDiagnosticsHotnessThreshold()) {
+    return;
+  }
+
   yaml::Output *Out = Ctx.getDiagnosticsOutputFile();
   if (Out) {
     auto *P = &const_cast<DiagnosticInfoOptimizationBase &>(OptDiagCommon);
diff --git a/llvm/lib/IR/LLVMContext.cpp b/llvm/lib/IR/LLVMContext.cpp
index ed3f10601bf..2e13f362344 100644
--- a/llvm/lib/IR/LLVMContext.cpp
+++ b/llvm/lib/IR/LLVMContext.cpp
@@ -132,6 +132,13 @@ bool LLVMContext::getDiagnosticsHotnessRequested() const {
   return pImpl->DiagnosticsHotnessRequested;
 }
 
+void LLVMContext::setDiagnosticsHotnessThreshold(uint64_t Threshold) {
+  pImpl->DiagnosticsHotnessThreshold = Threshold;
+}
+uint64_t LLVMContext::getDiagnosticsHotnessThreshold() const {
+  return pImpl->DiagnosticsHotnessThreshold;
+}
+
 yaml::Output *LLVMContext::getDiagnosticsOutputFile() {
   return pImpl->DiagnosticsOutputFile.get();
 }
diff --git a/llvm/lib/IR/LLVMContextImpl.h b/llvm/lib/IR/LLVMContextImpl.h
index 8f4450e9278..395beb57fe3 100644
--- a/llvm/lib/IR/LLVMContextImpl.h
+++ b/llvm/lib/IR/LLVMContextImpl.h
@@ -1170,6 +1170,7 @@ public:
   void *DiagnosticContext = nullptr;
   bool RespectDiagnosticFilters = false;
   bool DiagnosticsHotnessRequested = false;
+  uint64_t DiagnosticsHotnessThreshold = 0;
   std::unique_ptr<yaml::Output> DiagnosticsOutputFile;
 
   LLVMContext::YieldCallbackTy YieldCallback = nullptr;