[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

llvm/include/llvm/IR/LLVMContext.h

@@ -193,6 +193,15 @@ public:
   /// diagnostics.
   void setDiagnosticsHotnessRequested(bool Requested);
 
+  /// \brief Return the minimum hotness value a diagnostic would need in order
+  /// to be included in optimization diagnostics. If there is no minimum, this
+  /// returns None.
+  uint64_t getDiagnosticsHotnessThreshold() const;
+
+  /// \brief Set the minimum hotness value a diagnostic needs in order to be
+  /// included in optimization diagnostics.
+  void setDiagnosticsHotnessThreshold(uint64_t Threshold);
+
   /// \brief Return the YAML file used by the backend to save optimization
   /// diagnostics.  If null, diagnostics are not saved in a file but only
   /// emitted via the diagnostic handler.

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) {

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);

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();
 }

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;

llvm/test/CodeGen/AArch64/arm64-spill-remarks.ll

@@ -3,6 +3,15 @@
 ; RUN: llc < %s -mtriple=arm64-apple-ios7.0 -aarch64-neon-syntax=apple 2>&1 | FileCheck -check-prefix=NO_REMARK %s
 ; RUN: llc < %s -mtriple=arm64-apple-ios7.0 -aarch64-neon-syntax=apple -pass-remarks-output=%t.yaml -pass-remarks-with-hotness 2>&1 | FileCheck -check-prefix=NO_REMARK %s
 ; RUN: cat %t.yaml | FileCheck -check-prefix=YAML %s
+;
+; Verify that remarks below the hotness threshold are not output.
+; RUN: llc < %s -mtriple=arm64-apple-ios7.0 -aarch64-neon-syntax=apple -pass-remarks-missed=regalloc \
+; RUN:       -pass-remarks-with-hotness -pass-remarks-hotness-threshold=500 \
+; RUN:       2>&1 | FileCheck -check-prefix=THRESHOLD %s
+; RUN: llc < %s -mtriple=arm64-apple-ios7.0 -aarch64-neon-syntax=apple -pass-remarks-output=%t.threshold.yaml \
+; RUN:       -pass-remarks-with-hotness -pass-remarks-hotness-threshold=500 \
+; RUN:       2>&1 | FileCheck -check-prefix=NO_REMARK %s
+; RUN: cat %t.threshold.yaml | FileCheck -check-prefix=THRESHOLD_YAML %s
 
 ; This has two nested loops, each with one value that has to be spilled and
 ; then reloaded.
@@ -23,6 +32,9 @@
 
 ; NO_REMARK-NOT: remark
 
+; THRESHOLD-NOT: (hotness: 300)
+; THRESHOLD: remark: /tmp/kk.c:2:20: 1 spills 1 reloads generated in loop (hotness: 30000)
+
 ; YAML: --- !Missed
 ; YAML: Pass:            regalloc
 ; YAML: Name:            LoopSpillReload
@@ -63,6 +75,21 @@
 ; YAML:   - String:          generated in loop
 ; YAML: ...
 
+; THRESHOLD_YAML-NOT: Hotness:         300{{$}}
+; THRESHOLD_YAML: --- !Missed
+; THRESHOLD_YAML: Pass:            regalloc
+; THRESHOLD_YAML: Name:            LoopSpillReload
+; THRESHOLD_YAML: DebugLoc:        { File: /tmp/kk.c, Line: 2, Column: 20 }
+; THRESHOLD_YAML: Function:        fpr128
+; THRESHOLD_YAML: Hotness:         30000
+; THRESHOLD_YAML: Args:
+; THRESHOLD_YAML:   - NumSpills:       '1'
+; THRESHOLD_YAML:   - String:          ' spills '
+; THRESHOLD_YAML:   - NumReloads:      '1'
+; THRESHOLD_YAML:   - String:          ' reloads '
+; THRESHOLD_YAML:   - String:          generated in loop
+; THRESHOLD_YAML: ...
+
 define void @fpr128(<4 x float>* %p) nounwind ssp !prof !11 {
 entry:
   br label %loop, !dbg !8

llvm/test/Transforms/Inline/optimization-remarks-yaml.ll

@@ -1,8 +1,21 @@
-; RUN: opt < %s -S -inline -pass-remarks-missed=inline -pass-remarks-with-hotness \
+; RUN: opt < %s -S -inline -pass-remarks-missed=inline \
+; RUN:     -pass-remarks-with-hotness -pass-remarks-hotness-threshold 15 \
 ; RUN:     -pass-remarks-output=%t 2>&1 | FileCheck %s
 ; RUN: cat %t | FileCheck -check-prefix=YAML %s
 ; RUN: opt < %s -S -inline -pass-remarks-with-hotness -pass-remarks-output=%t
 ; RUN: cat %t | FileCheck -check-prefix=YAML %s
+;
+; Verify that remarks that don't meet the hotness threshold are not output.
+; RUN: opt < %s -S -inline -pass-remarks-missed=inline \
+; RUN:     -pass-remarks-with-hotness -pass-remarks-hotness-threshold 100 \
+; RUN:     -pass-remarks-output=%t.threshold 2>&1 | \
+; RUN:     FileCheck -check-prefix=THRESHOLD %s
+; RUN: test ! -s %t.threshold
+; RUN: opt < %s -S -inline \
+; RUN:     -pass-remarks-with-hotness -pass-remarks-hotness-threshold 100 \
+; RUN:     -pass-remarks-output=%t.threshold
+; The remarks output file should be empty.
+; RUN: test ! -s %t.threshold
 
 ; Check the YAML file generated for inliner remarks for this program:
 ;
@@ -43,6 +56,9 @@
 ; YAML-NEXT:   - String: ' because its definition is unavailable'
 ; YAML-NEXT: ...
 
+; No remarks should be output, since none meet the threshold.
+; THRESHOLD-NOT: remark
+
 ; ModuleID = '/tmp/s.c'
 source_filename = "/tmp/s.c"
 target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"

llvm/tools/llc/llc.cpp

@@ -149,6 +149,11 @@ static cl::opt<bool> PassRemarksWithHotness(
     cl::desc("With PGO, include profile count in optimization remarks"),
     cl::Hidden);
 
+static cl::opt<unsigned> PassRemarksHotnessThreshold(
+    "pass-remarks-hotness-threshold",
+    cl::desc("Minimum profile count required for an optimization remark to be output"),
+    cl::Hidden);
+
 static cl::opt<std::string>
     RemarksFilename("pass-remarks-output",
                     cl::desc("YAML output filename for pass remarks"),
@@ -325,6 +330,9 @@ int main(int argc, char **argv) {
   if (PassRemarksWithHotness)
     Context.setDiagnosticsHotnessRequested(true);
 
+  if (PassRemarksHotnessThreshold)
+    Context.setDiagnosticsHotnessThreshold(PassRemarksHotnessThreshold);
+
   std::unique_ptr<tool_output_file> YamlFile;
   if (RemarksFilename != "") {
     std::error_code EC;

llvm/tools/opt/opt.cpp

@@ -242,6 +242,11 @@ static cl::opt<bool> PassRemarksWithHotness(
     cl::desc("With PGO, include profile count in optimization remarks"),
     cl::Hidden);
 
+static cl::opt<unsigned> PassRemarksHotnessThreshold(
+    "pass-remarks-hotness-threshold",
+    cl::desc("Minimum profile count required for an optimization remark to be output"),
+    cl::Hidden);
+
 static cl::opt<std::string>
     RemarksFilename("pass-remarks-output",
                     cl::desc("YAML output filename for pass remarks"),
@@ -422,6 +427,9 @@ int main(int argc, char **argv) {
   if (PassRemarksWithHotness)
     Context.setDiagnosticsHotnessRequested(true);
 
+  if (PassRemarksHotnessThreshold)
+    Context.setDiagnosticsHotnessThreshold(PassRemarksHotnessThreshold);
+
   std::unique_ptr<tool_output_file> YamlFile;
   if (RemarksFilename != "") {
     std::error_code EC;