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[CSSPGO][llvm-profgen] Always report dangling probes for frames with real samples.

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Report dangling probes for frames that have real samples collected. Dangling probes are the probes associated to an empty block. When reported, sample count on a dangling probe will not be trusted by the compiler and we will rely on the counts inference algorithm to get the probe a reasonable count. This actually fixes a bug where previously only those dangling probes with samples collected were reported.

This patch also fixes two existing issues. Pseudo probes are stored in `Address2ProbesMap` and their pointers are used in `PseudoProbeInlineTree`. Previously `std::vector` was used to store probes and the pointers to probes may get obsolete as the vector grows. I'm changing `std::vector` to `std::list` instead.

The other issue is that all outlined functions shared the same inline frame previously due to the unchanged `Index` value as the dummy inlineSite identifier.

Good results seen for SPEC2017 in general regarding profile quality.

Reviewed By: wenlei, wlei

Differential Revision: https://reviews.llvm.org/D100235
This commit is contained in:
Hongtao Yu 2021-04-19 18:04:43 -07:00
parent 40b4beda19
commit 29e34b908b
7 changed files with 107 additions and 30 deletions
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1
include/llvm/MC/MCPseudoProbe.h
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@ -36,7 +36,6 @@
// A list of NUM_INLINED_FUNCTIONS entries describing each of the inlined
// callees. Each record contains:
// INLINE SITE
// GUID of the inlinee (uint64)
// ID of the callsite probe (ULEB128)
// FUNCTION BODY
// A FUNCTION BODY entry describing the inlined function.

5
test/tools/llvm-profgen/Inputs/inline-cs-dangling-pseudoprobe.perfscript Normal file
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@ -0,0 +1,5 @@
PERF_RECORD_MMAP2 595196/595196: [0x201000(0x1000) @ 0 00:1d 224227621 1042948]: r-xp /home/inline-cs-pseudoprobe.perfbin
20180e
5541f689495641d7
0x201858/0x20180e/P/-/-/0 0x20182b/0x20184d/P/-/-/0 0x20182b/0x201800/P/-/-/0 0x20182b/0x201800/P/-/-/0 0x20182b/0x201800/P/-/-/0 0x20182b/0x201800/P/-/-/0 0x20182b/0x201800/P/-/-/0 0x20182b/0x201800/P/-/-/0 0x20182b/0x201800/P/-/-/0 0x20182b/0x201800/P/-/-/0 0x20182b/0x201800/P/-/-/0 0x20182b/0x201800/P/-/-/0 0x20182b/0x201800/P/-/-/0 0x20182b/0x201800/P/-/-/0 0x20182b/0x201800/P/-/-/0 0x20182b/0x201800/P/-/-/0

51
test/tools/llvm-profgen/inline-cs-dangling-pseudoprobe.test Normal file
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@ -0,0 +1,51 @@
; RUN: llvm-profgen --perfscript=%S/Inputs/inline-cs-dangling-pseudoprobe.perfscript --binary=%S/Inputs/inline-cs-pseudoprobe.perfbin --output=%t --show-unwinder-output --csprof-cold-thres=0 | FileCheck %s --check-prefix=CHECK-UNWINDER
; RUN: FileCheck %s --input-file %t
; CHECK: [main:2 @ foo]:58:0
; CHECK-NEXT: 2: 15
; CHECK-NEXT: 3: 14
; CHECK-NEXT: 5: 14
; CHECK-NEXT: 6: 15
; CHECK-NEXT: !CFGChecksum: 138950591924
; CHECK:[main:2 @ foo:8 @ bar]:1:0
; CHECK-NEXT: 2: 18446744073709551615
; CHECK-NEXT: 3: 18446744073709551615
; CHECK-NEXT: 4: 1
; CHECK-NEXT: !CFGChecksum: 72617220756
; CHECK-UNWINDER: Binary(inline-cs-pseudoprobe.perfbin)'s Range Counter:
; CHECK-UNWINDER-EMPTY:
; CHECK-UNWINDER-NEXT: (800, 82b): 14
; CHECK-UNWINDER-NEXT: (84d, 858): 1
; CHECK-UNWINDER: Binary(inline-cs-pseudoprobe.perfbin)'s Branch Counter:
; CHECK-UNWINDER-EMPTY:
; CHECK-UNWINDER-NEXT: (82b, 800): 14
; CHECK-UNWINDER-NEXT: (82b, 84d): 1
; CHECK-UNWINDER-NEXT: (858, 80e): 1
; clang -O3 -fexperimental-new-pass-manager -fuse-ld=lld -fpseudo-probe-for-profiling
; -fno-omit-frame-pointer -mno-omit-leaf-frame-pointer -Xclang -mdisable-tail-calls
; -g test.c -o a.out
#include <stdio.h>
int bar(int x, int y) {
if (x % 3) {
return x - y;
}
return x + y;
}
void foo() {
int s, i = 0;
while (i++ < 4000 * 4000)
if (i % 91) s = bar(i, s); else s += 30;
printf("sum is %d\n", s);
}
int main() {
foo();
return 0;
}

14
test/tools/llvm-profgen/merge-cold-profile.test
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@ -1,17 +1,18 @@
; Used the data from recursion-compression.test, refer it for the unmerged output
; RUN: llvm-profgen --perfscript=%S/Inputs/recursion-compression-pseudoprobe.perfscript --binary=%S/Inputs/recursion-compression-pseudoprobe.perfbin --output=%t --compress-recursion=-1 --csprof-cold-thres=8
; RUN: FileCheck %s --input-file %t
; RUN: llvm-profgen --perfscript=%S/Inputs/recursion-compression-pseudoprobe.perfscript --binary=%S/Inputs/recursion-compression-pseudoprobe.perfbin --output=%t1 --compress-recursion=-1 --csprof-cold-thres=8
; RUN: FileCheck %s --input-file %t1
; Test --csprof-trim-cold-context=0
; RUN: llvm-profgen --perfscript=%S/Inputs/recursion-compression-pseudoprobe.perfscript --binary=%S/Inputs/recursion-compression-pseudoprobe.perfbin --output=%t --compress-recursion=-1 --csprof-cold-thres=100 --csprof-trim-cold-context=0
; RUN: FileCheck %s --input-file %t --check-prefix=CHECK-KEEP-COLD
; RUN: llvm-profgen --perfscript=%S/Inputs/recursion-compression-pseudoprobe.perfscript --binary=%S/Inputs/recursion-compression-pseudoprobe.perfbin --output=%t2 --compress-recursion=-1 --csprof-cold-thres=100 --csprof-trim-cold-context=0
; RUN: FileCheck %s --input-file %t2 --check-prefix=CHECK-KEEP-COLD
; Test --csprof-merge-cold-context=0
; RUN: llvm-profgen --perfscript=%S/Inputs/recursion-compression-pseudoprobe.perfscript --binary=%S/Inputs/recursion-compression-pseudoprobe.perfbin --output=%t --compress-recursion=-1 --csprof-cold-thres=10 --csprof-merge-cold-context=0
; RUN: FileCheck %s --input-file %t --check-prefix=CHECK-UNMERGED
; RUN: llvm-profgen --perfscript=%S/Inputs/recursion-compression-pseudoprobe.perfscript --binary=%S/Inputs/recursion-compression-pseudoprobe.perfbin --output=%t3 --compress-recursion=-1 --csprof-cold-thres=10 --csprof-merge-cold-context=0
; RUN: FileCheck %s --input-file %t3 --check-prefix=CHECK-UNMERGED
; CHECK: [fa]:14:4
; CHECK-NEXT: 1: 4
; CHECK-NEXT: 2: 18446744073709551615
; CHECK-NEXT: 3: 4
; CHECK-NEXT: 4: 2
; CHECK-NEXT: 5: 1
@ -37,6 +38,7 @@
; CHECK-KEEP-COLD-NEXT: !Attributes: 0
; CHECK-KEEP-COLD-NEXT:[fa]:14:4
; CHECK-KEEP-COLD-NEXT: 1: 4
; CHECK-KEEP-COLD-NEXT: 2: 18446744073709551615
; CHECK-KEEP-COLD-NEXT: 3: 4
; CHECK-KEEP-COLD-NEXT: 4: 2
; CHECK-KEEP-COLD-NEXT: 5: 1

35
tools/llvm-profgen/ProfileGenerator.cpp
View File

@ -510,22 +510,19 @@ void PseudoProbeCSProfileGenerator::populateBodySamplesWithProbes(
// Extract the top frame probes by looking up each address among the range in
// the Address2ProbeMap
extractProbesFromRange(RangeCounter, ProbeCounter, Binary);
std::unordered_map<PseudoProbeInlineTree *, FunctionSamples *> FrameSamples;
for (auto PI : ProbeCounter) {
const PseudoProbe *Probe = PI.first;
uint64_t Count = PI.second;
// Ignore dangling probes since they will be reported later if needed.
if (Probe->isDangling())
continue;
FunctionSamples &FunctionProfile =
getFunctionProfileForLeafProbe(ContextStrStack, Probe, Binary);
// Use InvalidProbeCount(UINT64_MAX) to mark sample count for a dangling
// probe. Dangling probes are the probes associated to an empty block. With
// this place holder, sample count on dangling probe will not be trusted by
// the compiler and it will rely on the counts inference algorithm to get
// the probe a reasonable count.
if (Probe->isDangling()) {
FunctionProfile.addBodySamplesForProbe(
Probe->Index, FunctionSamples::InvalidProbeCount);
continue;
}
// Record the current frame and FunctionProfile whenever samples are
// collected for non-danglie probes. This is for reporting all of the
// dangling probes of the frame later.
FrameSamples[Probe->getInlineTreeNode()] = &FunctionProfile;
FunctionProfile.addBodySamplesForProbe(Probe->Index, Count);
FunctionProfile.addTotalSamples(Count);
if (Probe->isEntry()) {
@ -554,6 +551,22 @@ void PseudoProbeCSProfileGenerator::populateBodySamplesWithProbes(
FunctionProfile.getContext().getNameWithoutContext(), Count);
}
}
// Report dangling probes for frames that have real samples collected.
// Dangling probes are the probes associated to an empty block. With this
// place holder, sample count on a dangling probe will not be trusted by the
// compiler and we will rely on the counts inference algorithm to get the
// probe a reasonable count. Use InvalidProbeCount to mark sample count for
// a dangling probe.
for (auto &I : FrameSamples) {
auto *FunctionProfile = I.second;
for (auto *Probe : I.first->getProbes()) {
if (Probe->isDangling()) {
FunctionProfile->addBodySamplesForProbe(
Probe->Index, FunctionSamples::InvalidProbeCount);
}
}
}
}
}

18
tools/llvm-profgen/PseudoProbe.cpp
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@ -198,7 +198,6 @@ void PseudoProbeDecoder::buildAddress2ProbeMap(const uint8_t *Start,
// A list of NUM_INLINED_FUNCTIONS entries describing each of the
// inlined callees. Each record contains:
// INLINE SITE
// GUID of the inlinee (uint64)
// Index of the callsite probe (ULEB128)
// FUNCTION BODY
// A FUNCTION BODY entry describing the inlined function.
@ -214,8 +213,11 @@ void PseudoProbeDecoder::buildAddress2ProbeMap(const uint8_t *Start,
uint32_t Index = 0;
// A DFS-based decoding
while (Data < End) {
// Read inline site for inlinees
if (Root != Cur) {
if (Root == Cur) {
// Use a sequential id for top level inliner.
Index = Root->getChildren().size();
} else {
// Read inline site for inlinees
Index = readUnsignedNumber<uint32_t>();
}
// Switch/add to a new tree node(inlinee)
@ -243,10 +245,10 @@ void PseudoProbeDecoder::buildAddress2ProbeMap(const uint8_t *Start,
Addr = readUnencodedNumber<int64_t>();
}
// Populate Address2ProbesMap
std::vector<PseudoProbe> &ProbeVec = Address2ProbesMap[Addr];
ProbeVec.emplace_back(Addr, Cur->GUID, Index, PseudoProbeType(Kind), Attr,
Cur);
Cur->addProbes(&ProbeVec.back());
auto &Probes = Address2ProbesMap[Addr];
Probes.emplace_back(Addr, Cur->GUID, Index, PseudoProbeType(Kind), Attr,
Cur);
Cur->addProbes(&Probes.back());
LastAddr = Addr;
}
@ -298,7 +300,7 @@ PseudoProbeDecoder::getCallProbeForAddr(uint64_t Address) const {
auto It = Address2ProbesMap.find(Address);
if (It == Address2ProbesMap.end())
return nullptr;
const std::vector<PseudoProbe> &Probes = It->second;
const auto &Probes = It->second;
const PseudoProbe *CallProbe = nullptr;
for (const auto &Probe : Probes) {

13
tools/llvm-profgen/PseudoProbe.h
View File

@ -45,9 +45,10 @@ class PseudoProbeInlineTree {
return std::get<0>(Site) ^ std::get<1>(Site);
}
};
std::unordered_map<InlineSite, std::unique_ptr<PseudoProbeInlineTree>,
InlineSiteHash>
Children;
using InlinedProbeTreeMap =
std::unordered_map<InlineSite, std::unique_ptr<PseudoProbeInlineTree>,
InlineSiteHash>;
InlinedProbeTreeMap Children;
public:
// Inlinee function GUID
@ -71,6 +72,8 @@ public:
return Ret.first->second.get();
}
InlinedProbeTreeMap &getChildren() { return Children; }
std::vector<PseudoProbe *> &getProbes() { return ProbeVector; }
void addProbes(PseudoProbe *Probe) { ProbeVector.push_back(Probe); }
// Return false if it's a dummy inline site
bool hasInlineSite() const { return std::get<0>(ISite) != 0; }
@ -91,7 +94,7 @@ struct PseudoProbeFuncDesc {
// GUID to PseudoProbeFuncDesc map
using GUIDProbeFunctionMap = std::unordered_map<uint64_t, PseudoProbeFuncDesc>;
// Address to pseudo probes map.
using AddressProbesMap = std::unordered_map<uint64_t, std::vector<PseudoProbe>>;
using AddressProbesMap = std::unordered_map<uint64_t, std::list<PseudoProbe>>;
/*
A pseudo probe has the format like below:
@ -135,6 +138,8 @@ struct PseudoProbe {
bool isDirectCall() const { return Type == PseudoProbeType::DirectCall; }
bool isCall() const { return isIndirectCall() || isDirectCall(); }
PseudoProbeInlineTree *getInlineTreeNode() const { return InlineTree; }
// Get the inlined context by traversing current inline tree backwards,
// each tree node has its InlineSite which is taken as the context.
// \p ContextStack is populated in root to leaf order