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

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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
This commit is contained in:
Hiroshi Yamauchi 2020-02-03 12:22:03 -08:00
parent 06f90b77ee
commit fcb2bf76aa
2 changed files with 28 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

12
include/llvm/Analysis/BlockFrequencyInfoImpl.h
View File

@ -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>

17
lib/Analysis/BlockFrequencyInfoImpl.cpp
View File

@ -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;
}