[PGO] Add option to always instrumenting loop entries #116789
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✅ With the latest revision this PR passed the C/C++ code formatter. |
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Dropped a bunch of nit comments. The general idea makes sense to me and I think we can soonish open this for general reviews of people experienced with these components.
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| // If true loop entries will be always instrumented. | |
| /// If true loop entries will be always instrumented. |
I'm aware that other parts of this file do not follow the style guide, so maybe it's better to stay consistent instead.
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Nice work 🙂
Dropped one more nit comment. Apart from this, this should be ready for a review of owners/maintainers of the PGO infra.
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@llvm/pr-subscribers-pgo @llvm/pr-subscribers-llvm-transforms Author: None (ronryvchin) ChangesThis patch extends the PGO infrastructure with an option to prefer the instrumentation of loop entry blocks. Note that change does NOT change the default behavior. Full diff: https://github.com/llvm/llvm-project/pull/116789.diff 4 Files Affected:
diff --git a/llvm/include/llvm/Transforms/Instrumentation/CFGMST.h b/llvm/include/llvm/Transforms/Instrumentation/CFGMST.h
index 35b3d615e3844a..8540f3103c23f5 100644
--- a/llvm/include/llvm/Transforms/Instrumentation/CFGMST.h
+++ b/llvm/include/llvm/Transforms/Instrumentation/CFGMST.h
@@ -19,6 +19,7 @@
#include "llvm/Analysis/BlockFrequencyInfo.h"
#include "llvm/Analysis/BranchProbabilityInfo.h"
#include "llvm/Analysis/CFG.h"
+#include "llvm/Analysis/LoopInfo.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/Support/BranchProbability.h"
@@ -52,10 +53,14 @@ template <class Edge, class BBInfo> class CFGMST {
BranchProbabilityInfo *const BPI;
BlockFrequencyInfo *const BFI;
+ LoopInfo *const LI;
// If function entry will be always instrumented.
const bool InstrumentFuncEntry;
+ // If true loop entries will be always instrumented.
+ const bool InstrumentLoopEntries;
+
// Find the root group of the G and compress the path from G to the root.
BBInfo *findAndCompressGroup(BBInfo *G) {
if (G->Group != G)
@@ -154,6 +159,11 @@ template <class Edge, class BBInfo> class CFGMST {
}
if (BPI != nullptr)
Weight = BPI->getEdgeProbability(&BB, TargetBB).scale(scaleFactor);
+ // If InstrumentLoopEntries is on and TargetBB is a loop head (i.e.,
+ // the current edge leads to a loop), set Weight to be minimal, so
+ // that the edge won't be chosen for the MST and will be instrumented.
+ if (InstrumentLoopEntries && LI->isLoopHeader(TargetBB))
+ Weight = 0;
if (Weight == 0)
Weight++;
auto *E = &addEdge(&BB, TargetBB, Weight);
@@ -291,10 +301,14 @@ template <class Edge, class BBInfo> class CFGMST {
return *AllEdges.back();
}
- CFGMST(Function &Func, bool InstrumentFuncEntry,
+ CFGMST(Function &Func, bool InstrumentFuncEntry, bool InstrumentLoopEntries,
BranchProbabilityInfo *BPI = nullptr,
- BlockFrequencyInfo *BFI = nullptr)
- : F(Func), BPI(BPI), BFI(BFI), InstrumentFuncEntry(InstrumentFuncEntry) {
+ BlockFrequencyInfo *BFI = nullptr, LoopInfo *LI = nullptr)
+ : F(Func), BPI(BPI), BFI(BFI), LI(LI),
+ InstrumentFuncEntry(InstrumentFuncEntry),
+ InstrumentLoopEntries(InstrumentLoopEntries) {
+ assert(!(InstrumentLoopEntries && !LI) &&
+ "expected a LoopInfo to instrumenting loop entries");
buildEdges();
sortEdgesByWeight();
computeMinimumSpanningTree();
diff --git a/llvm/lib/Transforms/Instrumentation/GCOVProfiling.cpp b/llvm/lib/Transforms/Instrumentation/GCOVProfiling.cpp
index 2ea89be40a3d46..f9be7f933d31e4 100644
--- a/llvm/lib/Transforms/Instrumentation/GCOVProfiling.cpp
+++ b/llvm/lib/Transforms/Instrumentation/GCOVProfiling.cpp
@@ -820,7 +820,8 @@ bool GCOVProfiler::emitProfileNotes(
SplitIndirectBrCriticalEdges(F, /*IgnoreBlocksWithoutPHI=*/false, BPI,
BFI);
- CFGMST<Edge, BBInfo> MST(F, /*InstrumentFuncEntry_=*/false, BPI, BFI);
+ CFGMST<Edge, BBInfo> MST(F, /*InstrumentFuncEntry=*/false,
+ /*InstrumentLoopEntries=*/false, BPI, BFI);
// getInstrBB can split basic blocks and push elements to AllEdges.
for (size_t I : llvm::seq<size_t>(0, MST.numEdges())) {
diff --git a/llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp b/llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp
index 4d8141431a0c19..ad68dcb7370507 100644
--- a/llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp
+++ b/llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp
@@ -259,6 +259,11 @@ static cl::opt<bool> PGOInstrumentEntry(
"pgo-instrument-entry", cl::init(false), cl::Hidden,
cl::desc("Force to instrument function entry basicblock."));
+static cl::opt<bool>
+ PGOInstrumentLoopEntries("pgo-instrument-loop-entries", cl::init(false),
+ cl::Hidden,
+ cl::desc("Force to instrument loop entries."));
+
static cl::opt<bool> PGOFunctionEntryCoverage(
"pgo-function-entry-coverage", cl::Hidden,
cl::desc(
@@ -359,6 +364,7 @@ class FunctionInstrumenter final {
std::unordered_multimap<Comdat *, GlobalValue *> &ComdatMembers;
BranchProbabilityInfo *const BPI;
BlockFrequencyInfo *const BFI;
+ LoopInfo *const LI;
const PGOInstrumentationType InstrumentationType;
@@ -376,14 +382,17 @@ class FunctionInstrumenter final {
InstrumentationType == PGOInstrumentationType::CTXPROF;
}
+ bool shouldInstrumentLoopEntries() const { return PGOInstrumentLoopEntries; }
+
public:
FunctionInstrumenter(
Module &M, Function &F, TargetLibraryInfo &TLI,
std::unordered_multimap<Comdat *, GlobalValue *> &ComdatMembers,
BranchProbabilityInfo *BPI = nullptr, BlockFrequencyInfo *BFI = nullptr,
+ LoopInfo *LI = nullptr,
PGOInstrumentationType InstrumentationType = PGOInstrumentationType::FDO)
: M(M), F(F), TLI(TLI), ComdatMembers(ComdatMembers), BPI(BPI), BFI(BFI),
- InstrumentationType(InstrumentationType) {}
+ LI(LI), InstrumentationType(InstrumentationType) {}
void instrument();
};
@@ -625,12 +634,13 @@ template <class Edge, class BBInfo> class FuncPGOInstrumentation {
Function &Func, TargetLibraryInfo &TLI,
std::unordered_multimap<Comdat *, GlobalValue *> &ComdatMembers,
bool CreateGlobalVar = false, BranchProbabilityInfo *BPI = nullptr,
- BlockFrequencyInfo *BFI = nullptr, bool IsCS = false,
- bool InstrumentFuncEntry = true, bool HasSingleByteCoverage = false)
+ BlockFrequencyInfo *BFI = nullptr, LoopInfo *LI = nullptr,
+ bool IsCS = false, bool InstrumentFuncEntry = true,
+ bool InstrumentLoopEntries = false, bool HasSingleByteCoverage = false)
: F(Func), IsCS(IsCS), ComdatMembers(ComdatMembers), VPC(Func, TLI),
TLI(TLI), ValueSites(IPVK_Last + 1),
SIVisitor(Func, HasSingleByteCoverage),
- MST(F, InstrumentFuncEntry, BPI, BFI),
+ MST(F, InstrumentFuncEntry, InstrumentLoopEntries, BPI, BFI, LI),
BCI(constructBCI(Func, HasSingleByteCoverage, InstrumentFuncEntry)) {
if (BCI && PGOViewBlockCoverageGraph)
BCI->viewBlockCoverageGraph();
@@ -916,9 +926,10 @@ void FunctionInstrumenter::instrument() {
const bool IsCtxProf = InstrumentationType == PGOInstrumentationType::CTXPROF;
FuncPGOInstrumentation<PGOEdge, PGOBBInfo> FuncInfo(
- F, TLI, ComdatMembers, /*CreateGlobalVar=*/!IsCtxProf, BPI, BFI,
+ F, TLI, ComdatMembers, /*CreateGlobalVar=*/!IsCtxProf, BPI, BFI, LI,
InstrumentationType == PGOInstrumentationType::CSFDO,
- shouldInstrumentEntryBB(), PGOBlockCoverage);
+ shouldInstrumentEntryBB(), shouldInstrumentLoopEntries(),
+ PGOBlockCoverage);
auto *const Name = IsCtxProf ? cast<GlobalValue>(&F) : FuncInfo.FuncNameVar;
auto *const CFGHash =
@@ -1136,11 +1147,13 @@ class PGOUseFunc {
PGOUseFunc(Function &Func, Module *Modu, TargetLibraryInfo &TLI,
std::unordered_multimap<Comdat *, GlobalValue *> &ComdatMembers,
BranchProbabilityInfo *BPI, BlockFrequencyInfo *BFIin,
- ProfileSummaryInfo *PSI, bool IsCS, bool InstrumentFuncEntry,
+ LoopInfo *LI, ProfileSummaryInfo *PSI, bool IsCS,
+ bool InstrumentFuncEntry, bool InstrumentLoopEntries,
bool HasSingleByteCoverage)
: F(Func), M(Modu), BFI(BFIin), PSI(PSI),
- FuncInfo(Func, TLI, ComdatMembers, false, BPI, BFIin, IsCS,
- InstrumentFuncEntry, HasSingleByteCoverage),
+ FuncInfo(Func, TLI, ComdatMembers, false, BPI, BFIin, LI, IsCS,
+ InstrumentFuncEntry, InstrumentLoopEntries,
+ HasSingleByteCoverage),
FreqAttr(FFA_Normal), IsCS(IsCS), VPC(Func, TLI) {}
void handleInstrProfError(Error Err, uint64_t MismatchedFuncSum);
@@ -1923,6 +1936,7 @@ static bool InstrumentAllFunctions(
Module &M, function_ref<TargetLibraryInfo &(Function &)> LookupTLI,
function_ref<BranchProbabilityInfo *(Function &)> LookupBPI,
function_ref<BlockFrequencyInfo *(Function &)> LookupBFI,
+ function_ref<LoopInfo *(Function &)> LookupLI,
PGOInstrumentationType InstrumentationType) {
// For the context-sensitve instrumentation, we should have a separated pass
// (before LTO/ThinLTO linking) to create these variables.
@@ -1943,10 +1957,11 @@ static bool InstrumentAllFunctions(
for (auto &F : M) {
if (skipPGOGen(F))
continue;
- auto &TLI = LookupTLI(F);
- auto *BPI = LookupBPI(F);
- auto *BFI = LookupBFI(F);
- FunctionInstrumenter FI(M, F, TLI, ComdatMembers, BPI, BFI,
+ TargetLibraryInfo &TLI = LookupTLI(F);
+ BranchProbabilityInfo *BPI = LookupBPI(F);
+ BlockFrequencyInfo *BFI = LookupBFI(F);
+ LoopInfo *LI = LookupLI(F);
+ FunctionInstrumenter FI(M, F, TLI, ComdatMembers, BPI, BFI, LI,
InstrumentationType);
FI.instrument();
}
@@ -1980,8 +1995,11 @@ PreservedAnalyses PGOInstrumentationGen::run(Module &M,
auto LookupBFI = [&FAM](Function &F) {
return &FAM.getResult<BlockFrequencyAnalysis>(F);
};
+ auto LookupLI = [&FAM](Function &F) {
+ return &FAM.getResult<LoopAnalysis>(F);
+ };
- if (!InstrumentAllFunctions(M, LookupTLI, LookupBPI, LookupBFI,
+ if (!InstrumentAllFunctions(M, LookupTLI, LookupBPI, LookupBFI, LookupLI,
InstrumentationType))
return PreservedAnalyses::all();
@@ -2116,7 +2134,8 @@ static bool annotateAllFunctions(
function_ref<TargetLibraryInfo &(Function &)> LookupTLI,
function_ref<BranchProbabilityInfo *(Function &)> LookupBPI,
function_ref<BlockFrequencyInfo *(Function &)> LookupBFI,
- ProfileSummaryInfo *PSI, bool IsCS) {
+ function_ref<LoopInfo *(Function &)> LookupLI, ProfileSummaryInfo *PSI,
+ bool IsCS) {
LLVM_DEBUG(dbgs() << "Read in profile counters: ");
auto &Ctx = M.getContext();
// Read the counter array from file.
@@ -2181,22 +2200,26 @@ static bool annotateAllFunctions(
bool InstrumentFuncEntry = PGOReader->instrEntryBBEnabled();
if (PGOInstrumentEntry.getNumOccurrences() > 0)
InstrumentFuncEntry = PGOInstrumentEntry;
+ bool InstrumentLoopEntries =
+ (PGOInstrumentLoopEntries.getNumOccurrences() > 0);
bool HasSingleByteCoverage = PGOReader->hasSingleByteCoverage();
for (auto &F : M) {
if (skipPGOUse(F))
continue;
- auto &TLI = LookupTLI(F);
- auto *BPI = LookupBPI(F);
- auto *BFI = LookupBFI(F);
+ TargetLibraryInfo &TLI = LookupTLI(F);
+ BranchProbabilityInfo *BPI = LookupBPI(F);
+ BlockFrequencyInfo *BFI = LookupBFI(F);
+ LoopInfo *LI = LookupLI(F);
if (!HasSingleByteCoverage) {
// Split indirectbr critical edges here before computing the MST rather
// than later in getInstrBB() to avoid invalidating it.
SplitIndirectBrCriticalEdges(F, /*IgnoreBlocksWithoutPHI=*/false, BPI,
BFI);
}
- PGOUseFunc Func(F, &M, TLI, ComdatMembers, BPI, BFI, PSI, IsCS,
- InstrumentFuncEntry, HasSingleByteCoverage);
+ PGOUseFunc Func(F, &M, TLI, ComdatMembers, BPI, BFI, LI, PSI, IsCS,
+ InstrumentFuncEntry, InstrumentLoopEntries,
+ HasSingleByteCoverage);
if (HasSingleByteCoverage) {
Func.populateCoverage(PGOReader.get());
continue;
@@ -2335,10 +2358,14 @@ PreservedAnalyses PGOInstrumentationUse::run(Module &M,
auto LookupBFI = [&FAM](Function &F) {
return &FAM.getResult<BlockFrequencyAnalysis>(F);
};
+ auto LookupLI = [&FAM](Function &F) {
+ return &FAM.getResult<LoopAnalysis>(F);
+ };
auto *PSI = &MAM.getResult<ProfileSummaryAnalysis>(M);
if (!annotateAllFunctions(M, ProfileFileName, ProfileRemappingFileName, *FS,
- LookupTLI, LookupBPI, LookupBFI, PSI, IsCS))
+ LookupTLI, LookupBPI, LookupBFI, LookupLI, PSI,
+ IsCS))
return PreservedAnalyses::all();
return PreservedAnalyses::none();
diff --git a/llvm/test/Transforms/PGOProfile/loop3.ll b/llvm/test/Transforms/PGOProfile/loop3.ll
new file mode 100644
index 00000000000000..7ffc3450d55ecb
--- /dev/null
+++ b/llvm/test/Transforms/PGOProfile/loop3.ll
@@ -0,0 +1,62 @@
+; RUN: opt %s -passes=pgo-instr-gen -pgo-instrument-loop-entries=false -S | FileCheck %s --check-prefixes=GEN,NOTLOOPENTRIES
+; RUN: opt %s -passes=pgo-instr-gen -pgo-instrument-loop-entries=true -S | FileCheck %s --check-prefixes=GEN,LOOPENTRIES
+; RUN: opt %s -passes=pgo-instr-gen -pgo-instrument-entry=true -S | FileCheck %s --check-prefixes=GEN,FUNCTIONENTRY
+
+; GEN: $__llvm_profile_raw_version = comdat any
+; GEN: @__llvm_profile_raw_version = hidden constant i64 {{[0-9]+}}, comdat
+; GEN: @__profn_test_simple_for_with_bypass = private constant [27 x i8] c"test_simple_for_with_bypass"
+
+define i32 @test_simple_for_with_bypass(i32 %n) {
+entry:
+; GEN: entry:
+; NOTLOOPENTRIES: call void @llvm.instrprof.increment(ptr @__profn_test_simple_for_with_bypass, i64 {{[0-9]+}}, i32 3, i32 1)
+; LOOPENTRIES: call void @llvm.instrprof.increment(ptr @__profn_test_simple_for_with_bypass, i64 {{[0-9]+}}, i32 3, i32 0)
+; FUNCTIONENTRY: call void @llvm.instrprof.increment(ptr @__profn_test_simple_for_with_bypass, i64 {{[0-9]+}}, i32 3, i32 0)
+ %mask = and i32 %n, 65535
+ %skip = icmp eq i32 %mask, 0
+ br i1 %skip, label %end, label %for.entry
+
+for.entry:
+; GEN: for.entry:
+; LOOPENTRIES: call void @llvm.instrprof.increment(ptr @__profn_test_simple_for_with_bypass, i64 {{[0-9]+}}, i32 3, i32 1)
+; NOTLOOPENTRIES-NOT: call void @llvm.instrprof.increment
+; FUNCTIONENTRY-NOT: call void @llvm.instrprof.increment
+ br label %for.cond
+
+for.cond:
+; GEN: for.cond:
+; GEN-NOT: call void @llvm.instrprof.increment
+ %i = phi i32 [ 0, %for.entry ], [ %inc1, %for.inc ]
+ %sum = phi i32 [ 1, %for.entry ], [ %inc, %for.inc ]
+ %cmp = icmp slt i32 %i, %n
+ br i1 %cmp, label %for.body, label %for.end, !prof !1
+
+for.body:
+; GEN: for.body:
+; GEN-NOT: call void @llvm.instrprof.increment
+ %inc = add nsw i32 %sum, 1
+ br label %for.inc
+
+for.inc:
+; GEN: for.inc:
+; NOTLOOPENTRIES: call void @llvm.instrprof.increment(ptr @__profn_test_simple_for_with_bypass, i64 {{[0-9]+}}, i32 3, i32 0)
+; LOOPENTRIES: call void @llvm.instrprof.increment(ptr @__profn_test_simple_for_with_bypass, i64 {{[0-9]+}}, i32 3, i32 2)
+; FUNCTIONENTRY: call void @llvm.instrprof.increment(ptr @__profn_test_simple_for_with_bypass, i64 {{[0-9]+}}, i32 3, i32 1)
+ %inc1 = add nsw i32 %i, 1
+ br label %for.cond
+
+for.end:
+; GEN: for.end:
+; NOTLOOPENTRIES: call void @llvm.instrprof.increment(ptr @__profn_test_simple_for_with_bypass, i64 {{[0-9]+}}, i32 3, i32 2)
+; FUNCTIONENTRY: call void @llvm.instrprof.increment(ptr @__profn_test_simple_for_with_bypass, i64 {{[0-9]+}}, i32 3, i32 2)
+; LOOPENTRIES-NOT: call void @llvm.instrprof.increment
+ br label %end
+
+end:
+; GEN: end:
+; GEN-NOT: call void @llvm.instrprof.increment
+ %final_sum = phi i32 [ %sum, %for.end ], [ 0, %entry ]
+ ret i32 %final_sum
+}
+
+!1 = !{!"branch_weights", i32 100000, i32 80}
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I think we also need to add a new variant mask for instrumenting loop entries. Otherwise we won't be able to match the profiles they generate correctly
llvm-project/llvm/lib/Transforms/Instrumentation/PGOInstrumentation.cpp
Lines 439 to 441 in dd78d7c
| }; | ||
| auto LookupLI = [&FAM](Function &F) { | ||
| return &FAM.getResult<LoopAnalysis>(F); | ||
| }; |
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Honestly I'm not sure why we don't simply pass the FAM rather than these lambdas, but this probably shouldn't block your work.
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@ellishg Do you know how |
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| #define VARIANT_MASK_IR_PROF (0x1ULL << 55) | ||
| #define VARIANT_MASK_CSIR_PROF (0x1ULL << 56) | ||
| #define VARIANT_MASK_INSTR_ENTRY (0x1ULL << 57) |
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To maintain backwards compatibility these bits cannot be changed. I guess we need to expand the mask to support more bits.
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Are bits 33-55 in use?
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I don't actually remember. I think VARIANT_MASK_IR_PROF was actually the first mask and later ones used higher bits. But we cannot go any higher. There might be some reason we started at 55. At first glance it seems that using bit 54 should be fine.
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I see that you are right (historically it started at 56 and climbed higher), but I cannot find usages of bit 55
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Considering that there is no usage of bit 55 and that there is no documentation about this being reserved, I would argue that we should be free to use 55. If any downstream user is relying on such an undocumented implementation detail, we should be free to break it.
llvm/test/Transforms/PGOProfile/Inputs/thinlto_indirect_call_promotion.profraw
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Thanks for asking. I think you should not need to change this test, especially since this flag is off by default. I suspect it is broken because the variant mask bits were changed. |
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This patch extends the PGO infrastructure with an option to prefer the instrumentation of loop entry blocks. This option is a generalization of llvm@19fb5b4, and helps to cover cases where the loop exit is never executed. An example where this can occur are event handling loops. Note that change does NOT change the default behavior.
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@ellishg Thank you for your comments! |
|
@ronryvchin Congratulations on having your first Pull Request (PR) merged into the LLVM Project! Your changes will be combined with recent changes from other authors, then tested by our build bots. If there is a problem with a build, you may receive a report in an email or a comment on this PR. Please check whether problems have been caused by your change specifically, as the builds can include changes from many authors. It is not uncommon for your change to be included in a build that fails due to someone else's changes, or infrastructure issues. How to do this, and the rest of the post-merge process, is covered in detail here. If your change does cause a problem, it may be reverted, or you can revert it yourself. This is a normal part of LLVM development. You can fix your changes and open a new PR to merge them again. If you don't get any reports, no action is required from you. Your changes are working as expected, well done! |
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This patch extends the PGO infrastructure with an option to prefer the instrumentation of loop entry blocks.
This option is a generalization of 19fb5b4,
and helps to cover cases where the loop exit is never executed.
An example where this can occur are event handling loops.
Note that change does NOT change the default behavior.