[llvm] r325823 - [ThinLTO] Represent relative BF using a scaled representation .
Easwaran Raman via llvm-commits
llvm-commits at lists.llvm.org
Thu Feb 22 11:44:08 PST 2018
Author: eraman
Date: Thu Feb 22 11:44:08 2018
New Revision: 325823
URL: http://llvm.org/viewvc/llvm-project?rev=325823&view=rev
Log:
[ThinLTO] Represent relative BF using a scaled representation .
Summary:
The current integer representation of relative block frequency prevents
representing relative block frequencies below 1. This change uses a 8 of
the 29 bits to represent the decimal part by using a fixed scale of -8.
Reviewers: tejohnson, davidxl
Subscribers: mehdi_amini, inglorion, llvm-commits
Differential Revision: https://reviews.llvm.org/D43520
Modified:
llvm/trunk/include/llvm/IR/ModuleSummaryIndex.h
llvm/trunk/lib/Analysis/ModuleSummaryAnalysis.cpp
llvm/trunk/test/Bitcode/thinlto-function-summary-callgraph-relbf.ll
Modified: llvm/trunk/include/llvm/IR/ModuleSummaryIndex.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/IR/ModuleSummaryIndex.h?rev=325823&r1=325822&r2=325823&view=diff
==============================================================================
--- llvm/trunk/include/llvm/IR/ModuleSummaryIndex.h (original)
+++ llvm/trunk/include/llvm/IR/ModuleSummaryIndex.h Thu Feb 22 11:44:08 2018
@@ -26,6 +26,7 @@
#include "llvm/IR/GlobalValue.h"
#include "llvm/IR/Module.h"
#include "llvm/Support/MathExtras.h"
+#include "llvm/Support/ScaledNumber.h"
#include <algorithm>
#include <array>
#include <cassert>
@@ -59,7 +60,11 @@ struct CalleeInfo {
// The size of the bit-field might need to be adjusted if more values are
// added to HotnessType enum.
uint32_t Hotness : 3;
+
+ /// The value stored in RelBlockFreq has to be interpreted as the digits of
+ /// a scaled number with a scale of \p -ScaleShift.
uint32_t RelBlockFreq : 29;
+ static constexpr int32_t ScaleShift = 8;
static constexpr uint64_t MaxRelBlockFreq = (1 << 29) - 1;
CalleeInfo()
@@ -73,10 +78,20 @@ struct CalleeInfo {
HotnessType getHotness() const { return HotnessType(Hotness); }
- // When there are multiple edges between the same (caller, callee) pair, the
- // relative block frequencies are summed up.
- void updateRelBlockFreq(uint64_t RBF) {
- uint64_t Sum = SaturatingAdd<uint64_t>(RelBlockFreq, RBF);
+ /// Update \p RelBlockFreq from \p BlockFreq and \p EntryFreq
+ ///
+ /// BlockFreq is divided by EntryFreq and added to RelBlockFreq. To represent
+ /// fractional values, the result is represented as a fixed point number with
+ /// scale of -ScaleShift.
+ void updateRelBlockFreq(uint64_t BlockFreq, uint64_t EntryFreq) {
+ if (EntryFreq == 0)
+ return;
+ using Scaled64 = ScaledNumber<uint64_t>;
+ Scaled64 Temp(BlockFreq, ScaleShift);
+ Temp /= Scaled64::get(EntryFreq);
+
+ uint64_t Sum =
+ SaturatingAdd<uint64_t>(Temp.toInt<uint64_t>(), RelBlockFreq);
Sum = std::min(Sum, uint64_t(MaxRelBlockFreq));
RelBlockFreq = static_cast<uint32_t>(Sum);
}
Modified: llvm/trunk/lib/Analysis/ModuleSummaryAnalysis.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ModuleSummaryAnalysis.cpp?rev=325823&r1=325822&r2=325823&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ModuleSummaryAnalysis.cpp (original)
+++ llvm/trunk/lib/Analysis/ModuleSummaryAnalysis.cpp Thu Feb 22 11:44:08 2018
@@ -279,17 +279,9 @@ computeFunctionSummary(ModuleSummaryInde
// Add the relative block frequency to CalleeInfo if there is no profile
// information.
if (BFI != nullptr && Hotness == CalleeInfo::HotnessType::Unknown) {
- auto BBFreq = BFI->getBlockFreq(&BB).getFrequency();
- // FIXME: This might need some scaling to prevent BBFreq values from
- // being rounded down to 0.
- auto EntryFreq = BFI->getEntryFreq();
- // Block frequencies can be directly set for a block and so we need to
- // handle the case of entry frequency being 0.
- if (EntryFreq)
- BBFreq /= EntryFreq;
- else
- BBFreq = 0;
- ValueInfo.updateRelBlockFreq(BBFreq);
+ uint64_t BBFreq = BFI->getBlockFreq(&BB).getFrequency();
+ uint64_t EntryFreq = BFI->getEntryFreq();
+ ValueInfo.updateRelBlockFreq(BBFreq, EntryFreq);
}
} else {
// Skip inline assembly calls.
Modified: llvm/trunk/test/Bitcode/thinlto-function-summary-callgraph-relbf.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Bitcode/thinlto-function-summary-callgraph-relbf.ll?rev=325823&r1=325822&r2=325823&view=diff
==============================================================================
--- llvm/trunk/test/Bitcode/thinlto-function-summary-callgraph-relbf.ll (original)
+++ llvm/trunk/test/Bitcode/thinlto-function-summary-callgraph-relbf.ll Thu Feb 22 11:44:08 2018
@@ -11,7 +11,7 @@
; CHECK: <GLOBALVAL_SUMMARY_BLOCK
; CHECK-NEXT: <VERSION
; See if the call to func is registered.
-; CHECK-NEXT: <PERMODULE_RELBF {{.*}} op4=1 {{.*}} op7=1
+; CHECK-NEXT: <PERMODULE_RELBF {{.*}} op4=1 {{.*}} op7=256
; CHECK-NEXT: </GLOBALVAL_SUMMARY_BLOCK>
; CHECK: <STRTAB_BLOCK
; CHECK-NEXT: blob data = 'undefinedglobmainfunc{{.*}}'
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