Add an option to hide "cold" blocks from CFG graph

Introduce a new cl::opt to hide "cold" blocks from CFG DOT graphs.
Use BFI to get block relative frequency. Hide the block if the
frequency is below the threshold set by the command line option value.

Reviewed By: davidxl, hoy
Differential Revision: https://reviews.llvm.org/D103640

1 files changed, 12 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/CFGPrinter.cpp b/llvm/lib/Analysis/CFGPrinter.cpp
index f9fb584..76f9f77 100644
--- a/llvm/lib/Analysis/CFGPrinter.cpp
+++ b/llvm/lib/Analysis/CFGPrinter.cpp
@@ -42,6 +42,10 @@ static cl::opt<bool> HideUnreachablePaths("cfg-hide-unreachable-paths",
 static cl::opt<bool> HideDeoptimizePaths("cfg-hide-deoptimize-paths",
                                          cl::init(false));
 
+static cl::opt<double> HideColdPaths(
+    "cfg-hide-cold-paths", cl::init(0.0),
+    cl::desc("Hide blocks with relative frequency below the given value"));
+
 static cl::opt<bool> ShowHeatColors("cfg-heat-colors", cl::init(true),
                                     cl::Hidden,
                                     cl::desc("Show heat colors in CFG"));
@@ -296,6 +300,14 @@ void DOTGraphTraits<DOTFuncInfo *>::computeDeoptOrUnreachablePaths(
 
 bool DOTGraphTraits<DOTFuncInfo *>::isNodeHidden(const BasicBlock *Node,
                                                  const DOTFuncInfo *CFGInfo) {
+  if (HideColdPaths.getNumOccurrences() > 0)
+    if (auto *BFI = CFGInfo->getBFI()) {
+      uint64_t NodeFreq = BFI->getBlockFreq(Node).getFrequency();
+      uint64_t EntryFreq = BFI->getEntryFreq();
+      // Hide blocks with relative frequency below HideColdPaths threshold.
+      if ((double)NodeFreq / EntryFreq < HideColdPaths)
+        return true;
+    }
   if (HideUnreachablePaths || HideDeoptimizePaths) {
     if (isOnDeoptOrUnreachablePath.find(Node) == 
         isOnDeoptOrUnreachablePath.end())