[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

1 files changed, 8 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/MachineOptimizationRemarkEmitter.cpp b/llvm/lib/CodeGen/MachineOptimizationRemarkEmitter.cpp
index 957028f..73c3428a 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);