[Bug tree-optimization/68235] gimple optimisations always use global -fmath-errno setting

["rsandifo at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68235

--- Comment #2 from rsandifo at gcc dot gnu.org <rsandifo at gcc dot gnu.org> ---
Author: rsandifo
Date: Sat Nov  7 09:58:32 2015
New Revision: 229917

URL: https://gcc.gnu.org/viewcvs?rev=229917&root=gcc&view=rev
Log:
Add -fno-math-errno to gcc.dg/lto/20110201-1_0.c

At the moment the ECF_* flags for a gimple call to a built-in
function are derived from the function decl, which in turn is
derived from the global command-line options.  So if the compiler
is run with -fno-math-errno, we always assume functions don't set
errno, regardless of local optimization options.  Similarly if the
compiler is run with -fmath-errno, we always assume functions set errno.

This shows up in gcc.dg/lto/20110201-1_0.c, where we compile
the file with -O0 and use -O2 -ffast-math for a specific function.
-O2 -ffast-math is enough for us to convert cabs to sqrt as hoped,
but because of the global -fmath-errno setting, we assume that the
call to sqrt is not pure or const and create vops for it.  This makes
it appear to the gimple code that a simple sqrt optab isn't enough.

Later patches move more decisions about maths functions to gimple
and think that in this case we should use:

        y = sqrt (x);
        if (!(x >= 0))
            sqrt (x); // to set errno.

This is being tracked as PR68235.  For now the patch adds
-fno-math-errno to the dg-options for this test.

Tested on x86_64-linux-gnu, aarch64-linux-gnu and arm-linux-gnueabi.

gcc/testsuite/
        PR tree-optimization/68235
        * gcc.dg/lto/20110201-1_0.c: Add -fno-math-errno.

Modified:
    trunk/gcc/testsuite/ChangeLog
    trunk/gcc/testsuite/gcc.dg/lto/20110201-1_0.c