[cfe-dev] operator==, Changing order of evaluation to expose bugs

[Nick Lewycky via cfe-dev]

Richard Smith wrote:
> Nick, did you ever put together a patch for this?

The work I did ended up here:

http://lists.cs.uiuc.edu/pipermail/cfe-commits/Week-of-Mon-20130114/071817.html

I don't think I ever reversed the order of 'foo() == bar()'.

>
> On Oct 10, 2015 11:46 AM, "Sergio Martins via cfe-dev"
> <cfe-dev at lists.llvm.org <mailto:cfe-dev at lists.llvm.org>> wrote:
>
>     Hi,
>
>     Consider:
>     if (foo() == bar())
>
>     it's up to the compiler to decide if it calls foo() or bar() first,
>     as the
>     standard doesn't guarantee any order.
>
>     Is there a way to force clang to evaluate first the rhs ?
>
>     I want to compile Qt with "evaluate rhs first" and check that
>     unit-tests still
>     pass, then rebuild with "evaluate lhs first".
>
>     Recenty we found some Qt code that relied on the order (undefined
>     behavior)
>     and it was discovered by compiling the code with MSVC2010, which
>     evaluated the
>     rhs first.
>
>
>     Regards,
>     Sérgio Martins
>
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