[BOLT] Fix boltedcollection and no_lbr order in fdata writer and parser

[zct]

when BAT and no_lbr are set at the same time, the perf2bolt writes boltedcollection first and then no_lbr

llvm-project/bolt/lib/Profile/DataAggregator.cpp

Lines 2219 to 2225 in e6f63a9

	if (BAT)
	OutFile << "boltedcollection\n";
	if (opts::BasicAggregation) {
	OutFile << "no_lbr";
	for (const StringMapEntry<std::nullopt_t> &Entry : EventNames)
	OutFile << " " << Entry.getKey();
	OutFile << "\n";

However, when used, llvm-bolt reads the no_lbr first, and then the boltedcollection

llvm-project/bolt/lib/Profile/DataReader.cpp

Lines 1175 to 1183 in e6f63a9

	ErrorOr<bool> FlagOrErr = maybeParseNoLBRFlag();
	if (!FlagOrErr)
	return FlagOrErr.getError();
	NoLBRMode = *FlagOrErr;
	ErrorOr<bool> BATFlagOrErr = maybeParseBATFlag();
	if (!BATFlagOrErr)
	return BATFlagOrErr.getError();
	BATMode = *BATFlagOrErr;

This causes an error when reading profile data，because the profile first line is boltedcollection，the maybeParseNoLBRFlag return false despite no_lbr was use

BOLT-INFO: pre-processing profile using branch profile reader
ERROR: no valid profile data found
BOLT-ERROR: 'cannot pre-process profile': Input/output error.

So we adjusted the order of the reads

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[aaupov]

Thank you for spotting an issue. Can you please add a trivial test case? Profile containing both lines in the wrong order.

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[zct]

@aaupov Here are the test cases
We can use any source code to reproduce, and I've constructed a simple use case here

https://pastebin.com/5uJ5kg8k

First we get a BOLT optimized binary(bolt_1), profile use no_lbr and enable BAT model

perf record -e cycles:up ./a.out
perf2bolt --nl -p perf.data -o perf.fdata ./a.out
llvm-bolt ./a.out -o bolt_1 -data perf.fdata  -reorder-blocks=ext-tsp -reorder-functions=hfsort+  -update-debug-sections -enable-bat

Then we use the profile collected from the bolt_1 and perform the second optimization, the error has occurred

perf record -e cycles:up ./bolt_1
perf2bolt --nl -p perf.data -o perf.fdata_2 ./bolt_1
llvm-bolt ./a.out -o bolt_2 -data perf.fdata_2  -reorder-blocks=ext-tsp -reorder-functions=hfsort+  -update-debug-sections -enable-bat

The contents of file perf.fdata_2

boltedcollection
no_lbr cycles:up:
1 _ZN9__gnu_cxxneIPiSt6vectorIiSaIiEEEEbRKNS_17__normal_iteratorIT_T0_EESA_ 36 1
1 _ZNK9__gnu_cxx17__normal_iteratorIPiSt6vectorIiSaIiEEEmiEl 39 1
1 _ZNSt6vectorIiSaIiEE4backEv 15 2
1 _ZNSt6vectorIiSaIiEE4backEv 4 1v

llvm-bolt errors

BOLT-INFO: shared object or position-independent executable detected
BOLT-INFO: Target architecture: x86_64
BOLT-INFO: BOLT version: e19b7dc36bc047b9eb72078d034596be766da350
BOLT-INFO: first alloc address is 0x0
BOLT-INFO: creating new program header table at address 0x200000, offset 0x200000
BOLT-INFO: enabling relocation mode
BOLT-INFO: enabling lite mode
BOLT-INFO: pre-processing profile using branch profile reader
ERROR: no valid profile data found
BOLT-ERROR: 'cannot pre-process profile': Input/output error.

The reason is what I said at the beginning about the order problem

[zct]

@aaupov ping

[aaupov]

Sorry, I meant a simple test with fdata profile containing the lines in the right order, and that BOLT succeeds reading it. Please check similar tests under bolt/test.