Comment 2 for bug 1845854

Hi Michael,

I agree that testing "Inf + -Inf" directly is not useful, and might even suggest removing that test as written rather than adding a compiler pragma. If we only check this in debug builds, and users will be running release builds, then I feel some of the usefulness of the test is lost.

So thinking again about epicsMathTest as you say, what we probably care about is an expression like "a + -b" being evaluated in code/calc record where a or b (or both) might be "Inf". If we rewrite epicsMathTest to do these sorts of tests rather than a direct "Inf + -Inf" etc. then I feel it is really testing what we care about, and currently all MSVC compiler versions pass tests written in this style.

Regards,

Freddie

-----Original Message-----
From: <email address hidden> <email address hidden> On Behalf Of mdavidsaver
Sent: 29 September 2019 18:28
To: Akeroyd, Freddie (STFC,RAL,ISIS) <email address hidden>
Subject: [Bug 1845854] Re: EPICS Math tests failing on Windows with MSVC

Taking a step back. I ask myself, what is epicsMathTest actually testing? To me it's about runtime behavior. "Inf + - Inf" is nonsense which wouldn't be found in a real source file, so the fact that the MSVC optimizer gets it wrong is interesting, but ultimately a distraction.

While not the best solution. Absent fine grained control of the optimizer, maybe the path forward is to disable optimizations (only) in epicsMathTest.c and/or epicsCalcTest.c ? Or at least around the NaN and Inf tests?

> #if defined(_MSC_VER)
> # pragma optimize("g", off)
> #endif

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https://bugs.launchpad.net/bugs/1845854

Title:
  EPICS Math tests failing on Windows with MSVC

Status in EPICS Base:
  New

Bug description:
  Some epics base tests involving NaN and Inf have been failing for most
  windows MSVC builds, I have written a small test program
  https://github.com/FreddieAkeroyd/Testing/blob/master/src/mytests/inftest.cpp
  with output at https://ci.appveyor.com/project/FreddieAkeroyd/testing
  which illustrates the underlying cause.

  The general summary is that:

  VS2010, VS2017 and VS2019 are OK in all configurations
  For other Visual studio versions:
      Debug builds are often OK
      All release builds fail.

  The failure mode is as follows (Inf shown here but applies to NaN
  too):

  Inf – Inf is evaluated correctly
  Inf + -Inf is evaluated incorrectly
  Inf + (-Inf) is evaluated correctly on VS 11.0 and 12.0, but not 14.0

  The test code is using expressions like “a + -a” with a = Inf, if it
  instead tests “a + -b” with a = b = Inf then release mode works in all
  cases. So it looks like the repeated variable name is causing an
  undesired optimisation. I feel expressions of the form “a + -b” rather
  than “a + -a” are a better reflection of what is likely in practice,
  if that change is acceptable then I would be happy to submit a PR to
  use different variable names within binary operation tests

  Regards,

  Freddie

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