From 803dd6fe6bb493e34a8747dc286a88aa05f353e1 Mon Sep 17 00:00:00 2001
From: Hiroshi Yamauchi <yamauchi@google.com>
Date: Mon, 3 Feb 2020 12:22:03 -0800
Subject: [PATCH] [BFI] Add a debug check for unknown block queries.

Summary:
Add a debug check for frequency queries for unknown blocks (typically blocks
that are created after BFI is computed but their frequencies are not
communicated to BFI.)

This is useful for detecting and debugging missed BFI updates.

This is debug build only and disabled behind a flag.

Reviewers: davidxl

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D73920
---
 llvm/include/llvm/Analysis/BlockFrequencyInfoImpl.h | 12 ++++++++++++
 llvm/lib/Analysis/BlockFrequencyInfoImpl.cpp        | 17 ++++++++++++++++-
 2 files changed, 28 insertions(+), 1 deletion(-)

diff --git a/llvm/include/llvm/Analysis/BlockFrequencyInfoImpl.h b/llvm/include/llvm/Analysis/BlockFrequencyInfoImpl.h
index 1b8832a..4d80591 100644
--- a/llvm/include/llvm/Analysis/BlockFrequencyInfoImpl.h
+++ b/llvm/include/llvm/Analysis/BlockFrequencyInfoImpl.h
@@ -26,6 +26,7 @@
 #include "llvm/IR/BasicBlock.h"
 #include "llvm/Support/BlockFrequency.h"
 #include "llvm/Support/BranchProbability.h"
+#include "llvm/Support/CommandLine.h"
 #include "llvm/Support/DOTGraphTraits.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/ErrorHandling.h"
@@ -46,6 +47,8 @@
 
 #define DEBUG_TYPE "block-freq"
 
+extern llvm::cl::opt<bool> CheckBFIUnknownBlockQueries;
+
 namespace llvm {
 
 class BranchProbabilityInfo;
@@ -1043,6 +1046,15 @@ void BlockFrequencyInfoImpl<BT>::calculate(const FunctionT &F,
   computeMassInFunction();
   unwrapLoops();
   finalizeMetrics();
+
+  if (CheckBFIUnknownBlockQueries) {
+    // To detect BFI queries for unknown blocks, add entries for unreachable
+    // blocks, if any. This is to distinguish between known/existing unreachable
+    // blocks and unknown blocks.
+    for (const BlockT &BB : F)
+      if (!Nodes.count(&BB))
+        setBlockFreq(&BB, 0);
+  }
 }
 
 template <class BT>
diff --git a/llvm/lib/Analysis/BlockFrequencyInfoImpl.cpp b/llvm/lib/Analysis/BlockFrequencyInfoImpl.cpp
index 0db6dd0..e4fda24 100644
--- a/llvm/lib/Analysis/BlockFrequencyInfoImpl.cpp
+++ b/llvm/lib/Analysis/BlockFrequencyInfoImpl.cpp
@@ -40,6 +40,12 @@ using namespace llvm::bfi_detail;
 
 #define DEBUG_TYPE "block-freq"
 
+cl::opt<bool> CheckBFIUnknownBlockQueries(
+    "check-bfi-unknown-block-queries",
+    cl::init(false), cl::Hidden,
+    cl::desc("Check if block frequency is queried for an unknown block "
+             "for debugging missed BFI updates"));
+
 ScaledNumber<uint64_t> BlockMass::toScaled() const {
   if (isFull())
     return ScaledNumber<uint64_t>(1, 0);
@@ -550,8 +556,17 @@ void BlockFrequencyInfoImplBase::finalizeMetrics() {
 
 BlockFrequency
 BlockFrequencyInfoImplBase::getBlockFreq(const BlockNode &Node) const {
-  if (!Node.isValid())
+  if (!Node.isValid()) {
+#ifndef NDEBUG
+    if (CheckBFIUnknownBlockQueries) {
+      SmallString<256> Msg;
+      raw_svector_ostream OS(Msg);
+      OS << "*** Detected BFI query for unknown block " << getBlockName(Node);
+      report_fatal_error(OS.str());
+    }
+#endif
     return 0;
+  }
   return Freqs[Node.Index].Integer;
 }
 
-- 
2.7.4