[PATCH] D73920: [BFI] Add a debug check for unknown block queries.

[Hiroshi Yamauchi via Phabricator via llvm-commits]

yamauchi created this revision.
yamauchi added a reviewer: davidxl.
Herald added a subscriber: hiraditya.
Herald added a project: LLVM.

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.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D73920

Files:
  llvm/include/llvm/Analysis/BlockFrequencyInfoImpl.h
  llvm/lib/Analysis/BlockFrequencyInfoImpl.cpp


Index: llvm/lib/Analysis/BlockFrequencyInfoImpl.cpp
===================================================================
--- llvm/lib/Analysis/BlockFrequencyInfoImpl.cpp
+++ llvm/lib/Analysis/BlockFrequencyInfoImpl.cpp
@@ -40,6 +40,12 @@
 
 #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 @@
 
 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;
 }
 
Index: llvm/include/llvm/Analysis/BlockFrequencyInfoImpl.h
===================================================================
--- llvm/include/llvm/Analysis/BlockFrequencyInfoImpl.h
+++ 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 @@
   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>


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