Bug 149408 – [JSC] access/nbody and math/partial-sums fails on x86 Linux without JIT

• Status: NEW
• Component: JavaScriptCore

[Csaba Osztrogonác]

$ JSC_useJIT=0 Tools/Scripts/run-sunspider --efl

...

{
    "3d-cube": 52,
    "3d-morph": 49,
    "3d-raytrace": 59,
    "access-binary-trees": 14,
    "access-fannkuch": 155,
    "access-nbody": NaN,
    "access-nsieve": 26,
    "bitops-3bit-bits-in-byte": 20,
    "bitops-bits-in-byte": 28,
    "bitops-bitwise-and": 22,
    "bitops-nsieve-bits": 72,
    "controlflow-recursive": 17,
    "crypto-aes": 67,
    "crypto-md5": 20,
    "crypto-sha1": 19,
    "date-format-tofte": 40,
    "date-format-xparb": 30,
    "math-cordic": 55,
    "math-partial-sums": NaN,
    "math-spectral-norm": 22,
    "regexp-dna": 12,
    "string-base64": 31,
    "string-fasta": 44,
    "string-tagcloud": 37,
    "string-unpack-code": 44,
    "string-validate-input": 22
}

...

============================================
RESULTS (means and 95% confidence intervals)
--------------------------------------------
Total:                    ERROR: Some tests failed.
--------------------------------------------

  3d:                   166.3ms +/- 4.4%
    cube:                55.9ms +/- 5.2%
    morph:               49.4ms +/- 4.1%
    raytrace:            61.0ms +/- 4.4%

  access:                 ERROR: Some tests failed.
    binary-trees:        13.8ms +/- 4.8%
    fannkuch:           159.3ms +/- 4.6%
    nbody:                ERROR: Invalid test run.
    nsieve:              26.7ms +/- 3.4%

  bitops:               146.1ms +/- 5.8%
    3bit-bits-in-byte:   20.0ms +/- 6.7%
    bits-in-byte:        29.1ms +/- 4.7%
    bitwise-and:         23.5ms +/- 16.2%
    nsieve-bits:         73.5ms +/- 3.9%

  controlflow:           17.3ms +/- 3.9%
    recursive:           17.3ms +/- 3.9%

  crypto:               110.8ms +/- 3.7%
    aes:                 69.6ms +/- 3.7%
    md5:                 21.0ms +/- 3.9%
    sha1:                20.2ms +/- 3.7%

  date:                  71.1ms +/- 2.5%
    format-tofte:        40.9ms +/- 3.0%
    format-xparb:        30.2ms +/- 2.7%

  math:                   ERROR: Some tests failed.
    cordic:              54.9ms +/- 3.5%
    partial-sums:         ERROR: Invalid test run.
    spectral-norm:       21.8ms +/- 3.4%

  regexp:                12.4ms +/- 4.0%
    dna:                 12.4ms +/- 4.0%

  string:               179.9ms +/- 2.8%
    base64:              31.0ms +/- 2.9%
    fasta:               44.5ms +/- 3.1%
    tagcloud:            37.6ms +/- 2.6%
    unpack-code:         44.8ms +/- 3.1%
    validate-input:      22.0ms +/- 2.7%

----

running these tests with run-jsc-stress-tests (after making it to run them with disabled JIT):

sunspider-1.0/access-nbody.js.no-jit: Exception: ERROR: bad result: expected -1.3524862408537381 but got -1.352486240853738
sunspider-1.0/access-nbody.js.no-jit: ERROR: Unexpected exit code: 3
sunspider-1.0/math-partial-sums.js.no-jit: Exception: ERROR: bad result: expected 60.08994194659945 but got 60.089941946599446
sunspider-1.0/math-partial-sums.js.no-jit: ERROR: Unexpected exit code: 3

Only the least significant digit is different, so it must be some rounding problem.

[Csaba Osztrogonác]

After a little bit investigation, I found the root of the bug.
The rounding error is caused by X87 instructions in LLINT.

If I disable X87, LLINT uses SSE2 and there are no rounding problem.