[TM] Restore default TargetOptions in TargetMachine::resetTargetOptions.

Summary:
Previously if you had

 * a function with the fast-math-enabled attr, followed by
 * a function without the fast-math attr,

the second function would inherit the first function's fast-math-ness.

This means that mixing fast-math and non-fast-math functions in a module
was completely broken unless you explicitly annotated every
non-fast-math function with "unsafe-fp-math"="false".  This appears to
have been broken since r176986 (March 2013), when the resetTargetOptions
function was introduced.

This patch tests the correct behavior as best we can.  I don't think I
can test FPDenormalMode and NoTrappingFPMath, because they aren't used
in any backends during function lowering.  Surprisingly, I also can't
find any uses at all of LessPreciseFPMAD affecting generated code.

The NVPTX/fast-math.ll test changes are an expected result of fixing
this bug.  When FMA is disabled, we emit add as "add.rn.f32", which
prevents fma combining.  Before this patch, fast-math was enabled in all
functions following the one which explicitly enabled it on itself, so we
were emitting plain "add.f32" where we should have generated
"add.rn.f32".

Reviewers: mkuper

Subscribers: hfinkel, majnemer, jholewinski, nemanjai, llvm-commits

Differential Revision: https://reviews.llvm.org/D28507

llvm-svn: 291618

0 files changed, 0 insertions, 0 deletions