Hi, all
Recently I’m trying to use LLVM PGO and autoFDO. However I have some problems in the process.
LLVM source code is updated on April 9th. Operating system is SUSE x86_64
-
Problems in instrumentation based PGO:
clang -O2 -fprofile-instr-generate test.c -o a.out
./a.out (then default.profraw is generated)
clang -O2 -fprofile-instr-use=default.profraw test.c -o a.out
error: pgo data file has malformed function entry
I found that the run-time function “writeFile” in InstrProfilingFile.cpp didn’t write ‘\n’.
But when parsing the profile data, in CodeGenPGO.cpp line 56, it tried to find ‘\n’ like below:
CurPtr = strchr(CurPtr, ‘\n’);
if (!CurPtr) {
ReportBadPGOData(CGM, “pgo data file has malformed function entry”);
return;
}
-
Problems in autoFDO:
Actually the problem happened in using create_llvm_prof, transformation is failed.
clang -O2 -g test.c -o a.out
perf record -b ./a.out (perf version is 0.0.2, “-b” option is not recognized, why?)
change to: perf record ./a.out (so perf.data is generated)
create_llvm_prof --binary=./a.out --out=code.prof (it read a.out and perf.data)
error: Malformed .note.gnu.build-id section
no build id found in the binary
it seems that a.out has no build id.
Someone who can help me?
Thanks,
Kaidong Chen
This error message from create_llvm_prof is actually harmless. Dehao
will be removing it at some point. The file code.prof should have
content and clang will be able to read it. Please try:
$ clang -fprofile-sample-use=code.prof -g ...
Diego.
Hi, all
Recently I’m trying to use LLVM PGO and autoFDO. However I have some problems in the process.
LLVM source code is updated on April 9th. Operating system is SUSE x86_64
- Problems in instrumentation based PGO:
clang -O2 -fprofile-instr-generate test.c -o a.out
./a.out (then default.profraw is generated)
clang -O2 -fprofile-instr-use=default.profraw test.c -o a.out
error: pgo data file has malformed function entry
I found that the run-time function “writeFile” in InstrProfilingFile.cpp didn’t write ‘\n’.
But when parsing the profile data, in CodeGenPGO.cpp line 56, it tried to find ‘\n’ like below:
CurPtr = strchr(CurPtr, ‘\n’);
if (!CurPtr) {
ReportBadPGOData(CGM, “pgo data file has malformed function entry”);
return;
}
Sorry that this isn’t documented very well. I’m working on some documentation for the instrumentation based profiling that should make this less of a guessing game.
You need to run llvm-profdata merge on the raw profile data to generate the format that clang understands. Something like:
llvm-profdata merge default.profraw -o default.profdata
Then use default.profdata as the input to -fprofile-instr-use.
Hi, all
Recently I’m trying to use LLVM PGO and autoFDO. However I have some problems in the process.
LLVM source code is updated on April 9th. Operating system is SUSE x86_64
- Problems in instrumentation based PGO:
clang -O2 -fprofile-instr-generate test.c -o a.out
./a.out (then default.profraw is generated)
clang -O2 -fprofile-instr-use=default.profraw test.c -o a.out
error: pgo data file has malformed function entry
I found that the run-time function “writeFile” in InstrProfilingFile.cpp didn’t write ‘\n’.
But when parsing the profile data, in CodeGenPGO.cpp line 56, it tried to find ‘\n’ like below:
CurPtr = strchr(CurPtr, ‘\n’);
if (!CurPtr) {
ReportBadPGOData(CGM, “pgo data file has malformed function entry”);
return;
}
Sorry that this isn’t documented very well. I’m working on some documentation for the instrumentation
based profiling that should make this less of a guessing game.
You need to run llvm-profdata merge on the raw profile data to generate the format that clang
understands. Something like:
llvm-profdata merge default.profraw -o default.profdata
Then use default.profdata as the input to -fprofile-instr-use.
It has worked well after I do as you say. Thank you!
And I want to confirm what passes benefits from profdata-guided feedback currently.
Is the profiledata feeded back to all of basicblock replacement, function inline, register allocation
and loop-unroll, or only basicblock replacement ?
I’ll test performance improvement of PGO on some benchmarks.
I think you already have some test results.
Thanks,
Kaidong Chen