[Clang][PGO][UserManual] Specify usage of -b flag

[madhur13490]

llvm-profgen cannot accept the perf profiles collected without -b and errors out with a message "Invalid perf script input!".

This can also be validated from the code in function checkPerfScriptType() in tools/llvm-profgen/PerfReader.cpp.

[llvmbot]

@llvm/pr-subscribers-clang

Author: Madhur Amilkanthwar (madhur13490)

Changes

llvm-profgen cannot accept the perf profiles collected without -b and errors out with a message "Invalid perf script input!".

This can also be validated from the code in function checkPerfScriptType() in tools/llvm-profgen/PerfReader.cpp.

---

Full diff: https://github.com/llvm/llvm-project/pull/139763.diff

1 Files Affected:

• (modified) clang/docs/UsersManual.rst (+3)

diff --git a/clang/docs/UsersManual.rst b/clang/docs/UsersManual.rst
index 6f804a10748d8..00899dcb8d8c2 100644
--- a/clang/docs/UsersManual.rst
+++ b/clang/docs/UsersManual.rst
@@ -2792,6 +2792,9 @@ usual build cycle when using sample profilers for optimization:
 
      $ llvm-profgen --binary=./code --output=code.prof --perfdata=perf.data
 
+   Please note, ``perf.data`` must be collected with ``-b`` flag to Linux ``perf``
+   for the above step to work.
+
    When using SEP the output is in the textual format corresponding to
    ``llvm-profgen --perfscript``. For example:
 

[tcreech-intel]

Thanks! Looks good to me.

Step 2 mentions -b, but makes it sound optional because it was optional with AutoFDO. Llvm-profgen doesn't have a mode to not require LBRs and this is good to point out.

[llvm-ci]

LLVM Buildbot has detected a new failure on builder llvm-clang-x86_64-gcc-ubuntu running on sie-linux-worker3 while building clang at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/174/builds/17728

Here is the relevant piece of the build log for the reference

Step 6 (test-build-unified-tree-check-all) failure: test (failure)
******************** TEST 'AddressSanitizer-x86_64-linux :: TestCases/asan_lsan_deadlock.cpp' FAILED ********************
Exit Code: 1

Command Output (stderr):
--
/home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/build/./bin/clang  --driver-mode=g++ -fsanitize=address -mno-omit-leaf-frame-pointer -fno-omit-frame-pointer -fno-optimize-sibling-calls -gline-tables-only  -m64  -O0 /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/llvm-project/compiler-rt/test/asan/TestCases/asan_lsan_deadlock.cpp -o /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/build/runtimes/runtimes-bins/compiler-rt/test/asan/X86_64LinuxConfig/TestCases/Output/asan_lsan_deadlock.cpp.tmp # RUN: at line 4
+ /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/build/./bin/clang --driver-mode=g++ -fsanitize=address -mno-omit-leaf-frame-pointer -fno-omit-frame-pointer -fno-optimize-sibling-calls -gline-tables-only -m64 -O0 /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/llvm-project/compiler-rt/test/asan/TestCases/asan_lsan_deadlock.cpp -o /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/build/runtimes/runtimes-bins/compiler-rt/test/asan/X86_64LinuxConfig/TestCases/Output/asan_lsan_deadlock.cpp.tmp
env ASAN_OPTIONS=detect_leaks=1 not  /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/build/runtimes/runtimes-bins/compiler-rt/test/asan/X86_64LinuxConfig/TestCases/Output/asan_lsan_deadlock.cpp.tmp 2>&1 | FileCheck /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/llvm-project/compiler-rt/test/asan/TestCases/asan_lsan_deadlock.cpp # RUN: at line 5
+ FileCheck /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/llvm-project/compiler-rt/test/asan/TestCases/asan_lsan_deadlock.cpp
+ env ASAN_OPTIONS=detect_leaks=1 not /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/build/runtimes/runtimes-bins/compiler-rt/test/asan/X86_64LinuxConfig/TestCases/Output/asan_lsan_deadlock.cpp.tmp
�[1m/home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/llvm-project/compiler-rt/test/asan/TestCases/asan_lsan_deadlock.cpp:58:12: �[0m�[0;1;31merror: �[0m�[1mCHECK: expected string not found in input
�[0m // CHECK: SUMMARY: AddressSanitizer: stack-buffer-overflow
�[0;1;32m           ^
�[0m�[1m<stdin>:1:1: �[0m�[0;1;30mnote: �[0m�[1mscanning from here
�[0m=================================================================
�[0;1;32m^
�[0m�[1m<stdin>:2:10: �[0m�[0;1;30mnote: �[0m�[1mpossible intended match here
�[0m==2764243==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7b50219de034 at pc 0x5642af832fb0 bp 0x7b501fbfdce0 sp 0x7b501fbfdcd8
�[0;1;32m         ^
�[0m
Input file: <stdin>
Check file: /home/buildbot/buildbot-root/llvm-clang-x86_64-gcc-ubuntu/llvm-project/compiler-rt/test/asan/TestCases/asan_lsan_deadlock.cpp

-dump-input=help explains the following input dump.

Input was:
<<<<<<
�[1m�[0m�[0;1;30m            1: �[0m�[1m�[0;1;46m================================================================= �[0m
�[0;1;31mcheck:58'0     X~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ error: no match found
�[0m�[0;1;30m            2: �[0m�[1m�[0;1;46m==2764243==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7b50219de034 at pc 0x5642af832fb0 bp 0x7b501fbfdce0 sp 0x7b501fbfdcd8 �[0m
�[0;1;31mcheck:58'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
�[0m�[0;1;35mcheck:58'1              ?                                                                                                                                    possible intended match
�[0m�[0;1;30m            3: �[0m�[1m�[0;1;46mWRITE of size 4 at 0x7b50219de034 thread T2 �[0m
�[0;1;31mcheck:58'0     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
�[0m>>>>>>

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