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[clang] Add flag to experiment with cold function attributes #89298

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Apr 19, 2024
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[clang] Add flag to experiment with cold function attributes #89298

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57 changes: 35 additions & 22 deletions clang/lib/CodeGen/BackendUtil.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -104,6 +104,21 @@ static cl::opt<bool> ClSanitizeOnOptimizerEarlyEP(
"sanitizer-early-opt-ep", cl::Optional,
cl::desc("Insert sanitizers on OptimizerEarlyEP."));

// Experiment to mark cold functions as optsize/minsize/optnone.
// TODO: remove once this is exposed as a proper driver flag.
static cl::opt<PGOOptions::ColdFuncOpt> ClPGOColdFuncAttr(
"pgo-cold-func-opt", cl::init(PGOOptions::ColdFuncOpt::Default), cl::Hidden,
cl::desc(
"Function attribute to apply to cold functions as determined by PGO"),
cl::values(clEnumValN(PGOOptions::ColdFuncOpt::Default, "default",
"Default (no attribute)"),
clEnumValN(PGOOptions::ColdFuncOpt::OptSize, "optsize",
"Mark cold functions with optsize."),
clEnumValN(PGOOptions::ColdFuncOpt::MinSize, "minsize",
"Mark cold functions with minsize."),
clEnumValN(PGOOptions::ColdFuncOpt::OptNone, "optnone",
"Mark cold functions with optnone.")));

extern cl::opt<InstrProfCorrelator::ProfCorrelatorKind> ProfileCorrelate;

// Re-link builtin bitcodes after optimization
Expand Down Expand Up @@ -768,42 +783,41 @@ void EmitAssemblyHelper::RunOptimizationPipeline(
CodeGenOpts.InstrProfileOutput.empty() ? getDefaultProfileGenName()
: CodeGenOpts.InstrProfileOutput,
"", "", CodeGenOpts.MemoryProfileUsePath, nullptr, PGOOptions::IRInstr,
PGOOptions::NoCSAction, PGOOptions::ColdFuncOpt::Default,
PGOOptions::NoCSAction, ClPGOColdFuncAttr,
CodeGenOpts.DebugInfoForProfiling,
/*PseudoProbeForProfiling=*/false, CodeGenOpts.AtomicProfileUpdate);
else if (CodeGenOpts.hasProfileIRUse()) {
// -fprofile-use.
auto CSAction = CodeGenOpts.hasProfileCSIRUse() ? PGOOptions::CSIRUse
: PGOOptions::NoCSAction;
PGOOpt = PGOOptions(
CodeGenOpts.ProfileInstrumentUsePath, "",
CodeGenOpts.ProfileRemappingFile, CodeGenOpts.MemoryProfileUsePath, VFS,
PGOOptions::IRUse, CSAction, PGOOptions::ColdFuncOpt::Default,
CodeGenOpts.DebugInfoForProfiling);
PGOOpt = PGOOptions(CodeGenOpts.ProfileInstrumentUsePath, "",
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could you do a clang-format, commit and rebase? This and the stuff at line 812 seems mostly that. Or does adding the ClPGOCouldFuncAttr mess up formatting?

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running clang-format on this file at main doesn't change these lines, so it seems like it is ClPGOCouldFuncAttr

CodeGenOpts.ProfileRemappingFile,
CodeGenOpts.MemoryProfileUsePath, VFS,
PGOOptions::IRUse, CSAction, ClPGOColdFuncAttr,
CodeGenOpts.DebugInfoForProfiling);
} else if (!CodeGenOpts.SampleProfileFile.empty())
// -fprofile-sample-use
PGOOpt = PGOOptions(
CodeGenOpts.SampleProfileFile, "", CodeGenOpts.ProfileRemappingFile,
CodeGenOpts.MemoryProfileUsePath, VFS, PGOOptions::SampleUse,
PGOOptions::NoCSAction, PGOOptions::ColdFuncOpt::Default,
PGOOptions::NoCSAction, ClPGOColdFuncAttr,
CodeGenOpts.DebugInfoForProfiling, CodeGenOpts.PseudoProbeForProfiling);
else if (!CodeGenOpts.MemoryProfileUsePath.empty())
// -fmemory-profile-use (without any of the above options)
PGOOpt = PGOOptions("", "", "", CodeGenOpts.MemoryProfileUsePath, VFS,
PGOOptions::NoAction, PGOOptions::NoCSAction,
PGOOptions::ColdFuncOpt::Default,
CodeGenOpts.DebugInfoForProfiling);
ClPGOColdFuncAttr, CodeGenOpts.DebugInfoForProfiling);
else if (CodeGenOpts.PseudoProbeForProfiling)
// -fpseudo-probe-for-profiling
PGOOpt = PGOOptions("", "", "", /*MemoryProfile=*/"", nullptr,
PGOOptions::NoAction, PGOOptions::NoCSAction,
PGOOptions::ColdFuncOpt::Default,
CodeGenOpts.DebugInfoForProfiling, true);
PGOOpt =
PGOOptions("", "", "", /*MemoryProfile=*/"", nullptr,
PGOOptions::NoAction, PGOOptions::NoCSAction,
ClPGOColdFuncAttr, CodeGenOpts.DebugInfoForProfiling, true);
else if (CodeGenOpts.DebugInfoForProfiling)
// -fdebug-info-for-profiling
PGOOpt = PGOOptions("", "", "", /*MemoryProfile=*/"", nullptr,
PGOOptions::NoAction, PGOOptions::NoCSAction,
PGOOptions::ColdFuncOpt::Default, true);
ClPGOColdFuncAttr, true);

// Check to see if we want to generate a CS profile.
if (CodeGenOpts.hasProfileCSIRInstr()) {
Expand All @@ -820,14 +834,13 @@ void EmitAssemblyHelper::RunOptimizationPipeline(
: CodeGenOpts.InstrProfileOutput;
PGOOpt->CSAction = PGOOptions::CSIRInstr;
} else
PGOOpt =
PGOOptions("",
CodeGenOpts.InstrProfileOutput.empty()
? getDefaultProfileGenName()
: CodeGenOpts.InstrProfileOutput,
"", /*MemoryProfile=*/"", nullptr, PGOOptions::NoAction,
PGOOptions::CSIRInstr, PGOOptions::ColdFuncOpt::Default,
CodeGenOpts.DebugInfoForProfiling);
PGOOpt = PGOOptions("",
CodeGenOpts.InstrProfileOutput.empty()
? getDefaultProfileGenName()
: CodeGenOpts.InstrProfileOutput,
"", /*MemoryProfile=*/"", nullptr,
PGOOptions::NoAction, PGOOptions::CSIRInstr,
ClPGOColdFuncAttr, CodeGenOpts.DebugInfoForProfiling);
}
if (TM)
TM->setPGOOption(PGOOpt);
Expand Down
12 changes: 12 additions & 0 deletions clang/test/CodeGen/pgo-force-function-attrs.ll
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Original file line number Diff line number Diff line change
@@ -0,0 +1,12 @@
; RUN: %clang_cc1 -O2 -mllvm -pgo-cold-func-opt=optsize -mllvm -enable-pgo-force-function-attrs -fprofile-sample-use=%S/Inputs/pgo-sample.prof %s -emit-llvm -o - | FileCheck %s --check-prefix=OPTSIZE
; Check that no profile means no optsize
; RUN: %clang_cc1 -O2 -mllvm -pgo-cold-func-opt=optsize -mllvm -enable-pgo-force-function-attrs %s -emit-llvm -o - | FileCheck %s --check-prefix=NONE
; Check that no -pgo-cold-func-opt=optsize means no optsize
; RUN: %clang_cc1 -O2 -mllvm -enable-pgo-force-function-attrs -fprofile-sample-use=%S/Inputs/pgo-sample.prof %s -emit-llvm -o - | FileCheck %s --check-prefix=NONE

; NONE-NOT: optsize
; OPTSIZE: optsize

define void @f() cold {
ret void
}
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