[PATCH] D43520: [ThinLTO] Represent relative BF using a scaled representation .
Easwaran Raman via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Tue Feb 20 11:35:59 PST 2018
eraman created this revision.
eraman added reviewers: tejohnson, davidxl.
Herald added subscribers: inglorion, mehdi_amini.
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.
Repository:
rL LLVM
https://reviews.llvm.org/D43520
Files:
include/llvm/IR/ModuleSummaryIndex.h
lib/Analysis/ModuleSummaryAnalysis.cpp
test/Bitcode/thinlto-function-summary-callgraph-relbf.ll
Index: test/Bitcode/thinlto-function-summary-callgraph-relbf.ll
===================================================================
--- test/Bitcode/thinlto-function-summary-callgraph-relbf.ll
+++ test/Bitcode/thinlto-function-summary-callgraph-relbf.ll
@@ -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{{.*}}'
Index: lib/Analysis/ModuleSummaryAnalysis.cpp
===================================================================
--- lib/Analysis/ModuleSummaryAnalysis.cpp
+++ lib/Analysis/ModuleSummaryAnalysis.cpp
@@ -279,17 +279,9 @@
// 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.
Index: include/llvm/IR/ModuleSummaryIndex.h
===================================================================
--- include/llvm/IR/ModuleSummaryIndex.h
+++ include/llvm/IR/ModuleSummaryIndex.h
@@ -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>
@@ -60,6 +61,7 @@
// added to HotnessType enum.
uint32_t Hotness : 3;
uint32_t RelBlockFreq : 29;
+ static constexpr int32_t ScaleShift = 8;
static constexpr uint64_t MaxRelBlockFreq = (1 << 29) - 1;
CalleeInfo()
@@ -73,10 +75,18 @@
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) {
+ 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);
}
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