[llvm-bugs] [Bug 39748] New: Regression(r347379): __tsan_{read, write}8 are ~10% slower

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https://bugs.llvm.org/show_bug.cgi?id=39748

            Bug ID: 39748
           Summary: Regression(r347379): __tsan_{read,write}8 are ~10%
                    slower
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Global Analyses
          Assignee: unassignedbugs at nondot.org
          Reporter: peter at pcc.me.uk
                CC: llvm-bugs at lists.llvm.org

It seems that r347379 has had the effect of making the __tsan_read8 and
__tsan_write8 functions about 10% slower. These functions are performance
critical since they are called on every 64-bit load and store in a
tsan-instrumented function. This was caught by the
sanitizer-x86_64-linux-autoconf bot:
http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux-autoconf/builds/31402/steps/tsan%20analyze/logs/stdio

I can observe the regression on my local machine like this:

$ projects/compiler-rt/lib/tsan/tests/rtl/TsanRtlTest-x86_64-Test 
--gtest_also_run_disabled_tests --gtest_filter=DISABLED_BENCH.Mop8*
Note: Google Test filter = DISABLED_BENCH.Mop8*
[==========] Running 3 tests from 1 test case.
[----------] Global test environment set-up.
[----------] 3 tests from DISABLED_BENCH
[ RUN      ] DISABLED_BENCH.Mop8
[       OK ] DISABLED_BENCH.Mop8 (74 ms)
[ RUN      ] DISABLED_BENCH.Mop8Read
[       OK ] DISABLED_BENCH.Mop8Read (820 ms)
[ RUN      ] DISABLED_BENCH.Mop8Write
[       OK ] DISABLED_BENCH.Mop8Write (817 ms)
[----------] 3 tests from DISABLED_BENCH (1711 ms total)

[----------] Global test environment tear-down
[==========] 3 tests from 1 test case ran. (1711 ms total)
[  PASSED  ] 3 tests.
$ projects/compiler-rt/lib/tsan/tests/rtl/TsanRtlTest-x86_64-Test1 
--gtest_also_run_disabled_tests --gtest_filter=DISABLED_BENCH.Mop8*
Note: Google Test filter = DISABLED_BENCH.Mop8*
[==========] Running 3 tests from 1 test case.
[----------] Global test environment set-up.
[----------] 3 tests from DISABLED_BENCH
[ RUN      ] DISABLED_BENCH.Mop8
[       OK ] DISABLED_BENCH.Mop8 (91 ms)
[ RUN      ] DISABLED_BENCH.Mop8Read
[       OK ] DISABLED_BENCH.Mop8Read (905 ms)
[ RUN      ] DISABLED_BENCH.Mop8Write
[       OK ] DISABLED_BENCH.Mop8Write (889 ms)
[----------] 3 tests from DISABLED_BENCH (1885 ms total)

[----------] Global test environment tear-down
[==========] 3 tests from 1 test case ran. (1885 ms total)
[  PASSED  ] 3 tests.

and the timings are reasonably consistent between runs.

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