Clear the upper half of a V4SFmode operand register in front of all
potentially trapping instructions. The testcase:

--cut here--
typedef float v2sf __attribute__((vector_size(8)));
typedef float v4sf __attribute__((vector_size(16)));

v2sf test(v4sf x, v4sf y)
{
  v2sf x2, y2;

  x2 = __builtin_shufflevector (x, x, 0, 1);
  y2 = __builtin_shufflevector (y, y, 0, 1);

  return x2 + y2;
}
--cut here--

now compiles to:

        movq    %xmm1, %xmm1    # 9     [c=4 l=4]  *vec_concatv4sf_0
        movq    %xmm0, %xmm0    # 10    [c=4 l=4]  *vec_concatv4sf_0
        addps   %xmm1, %xmm0    # 11    [c=12 l=3]  *addv4sf3/0

This approach addresses issues with exceptions, as well as issues with
denormal/invalid values. An obvious exception to the rule is a division,
where the value != 0.0 should be loaded into the upper half of the
denominator to avoid division by zero exception.

The patch effectively tightens the solution from PR95046 by clearing upper
halves of all operand registers before every potentially trapping instruction.
The testcase:

--cut here--
typedef float __attribute__((vector_size(8))) v2sf;

v2sf test (v2sf a, v2sf b, v2sf c)
{
  return a * b - c;
}
--cut here--

compiles to:

        movq    %xmm1, %xmm1    # 8     [c=4 l=4]  *vec_concatv4sf_0
        movq    %xmm0, %xmm0    # 9     [c=4 l=4]  *vec_concatv4sf_0
        movq    %xmm2, %xmm2    # 12    [c=4 l=4]  *vec_concatv4sf_0
        mulps   %xmm1, %xmm0    # 10    [c=16 l=3]  *mulv4sf3/0
        movq    %xmm0, %xmm0    # 13    [c=4 l=4]  *vec_concatv4sf_0
        subps   %xmm2, %xmm0    # 14    [c=12 l=3]  *subv4sf3/0

The implementation emits V4SFmode operation, so we can remove all "emulated"
SSE2 V2SFmode trapping instructions and remove "emulated" SSE2 V2SFmode
alternatives from 3dNOW! insn patterns.

    PR target/110762

gcc/ChangeLog:

    * config/i386/i386.md (plusminusmult): New code iterator.
    * config/i386/mmx.md (mmxdoublevecmode): New mode attribute.
    (movq_<mode>_to_sse): New expander.
    (<plusminusmult:insn>v2sf3): Macroize expander from addv2sf3,
    subv2sf3 and mulv2sf3 using plusminusmult code iterator.  Rewrite
    as a wrapper around V4SFmode operation.
    (mmx_addv2sf3): Change operand 1 and operand 2 predicates to
    nonimmediate_operand.
    (*mmx_addv2sf3): Remove SSE alternatives.  Change operand 1 and
    operand 2 predicates to nonimmediate_operand.
    (mmx_subv2sf3): Change operand 2 predicate to nonimmediate_operand.
    (mmx_subrv2sf3): Change operand 1 predicate to nonimmediate_operand.
    (*mmx_subv2sf3): Remove SSE alternatives.  Change operand 1 and
    operand 2 predicates to nonimmediate_operand.
    (mmx_mulv2sf3): Change operand 1 and operand 2 predicates to
    nonimmediate_operand.
    (*mmx_mulv2sf3): Remove SSE alternatives.  Change operand 1 and
    operand 2 predicates to nonimmediate_operand.
    (divv2sf3): Rewrite as a wrapper around V4SFmode operation.
    (<smaxmin:code>v2sf3): Ditto.
    (mmx_<smaxmin:code>v2sf3): Change operand 1 and operand 2
    predicates to nonimmediate_operand.
    (*mmx_<smaxmin:code>v2sf3): Remove SSE alternatives.  Change
    operand 1 and operand 2 predicates to nonimmediate_operand.
    (mmx_ieee_<ieee_maxmin>v2sf3): Ditto.
    (sqrtv2sf2): Rewrite as a wrapper around V4SFmode operation.
    (*mmx_haddv2sf3_low): Ditto.
    (*mmx_hsubv2sf3_low): Ditto.
    (vec_addsubv2sf3): Ditto.
    (*mmx_maskcmpv2sf3_comm): Remove.
    (*mmx_maskcmpv2sf3): Remove.
    (vec_cmpv2sfv2si): Rewrite as a wrapper around V4SFmode operation.
    (vcond<V2FI:mode>v2sf): Ditto.
    (fmav2sf4): Ditto.
    (fmsv2sf4): Ditto.
    (fnmav2sf4): Ditto.
    (fnmsv2sf4): Ditto.
    (fix_truncv2sfv2si2): Ditto.
    (fixuns_truncv2sfv2si2): Ditto.
    (mmx_fix_truncv2sfv2si2): Remove SSE alternatives.
    Change operand 1 predicate to nonimmediate_operand.
    (floatv2siv2sf2): Rewrite as a wrapper around V4SFmode operation.
    (floatunsv2siv2sf2): Ditto.
    (mmx_floatv2siv2sf2): Remove SSE alternatives.
    Change operand 1 predicate to nonimmediate_operand.
    (nearbyintv2sf2): Rewrite as a wrapper around V4SFmode operation.
    (rintv2sf2): Ditto.
    (lrintv2sfv2si2): Ditto.
    (ceilv2sf2): Ditto.
    (lceilv2sfv2si2): Ditto.
    (floorv2sf2): Ditto.
    (lfloorv2sfv2si2): Ditto.
    (btruncv2sf2): Ditto.
    (roundv2sf2): Ditto.
    (lroundv2sfv2si2): Ditto.
    (*mmx_roundv2sf2): Remove.

gcc/testsuite/ChangeLog:

    * gcc.target/i386/pr110762.c: New test.

Bootstrapped and regression tested on x86_64-linux-gnu {,-m32}.

Uros.