[PATCH, i386] Avoid 512-bit vector return constant for Intel AVX512 configuration

[Shalnov, Sergey]

Hi,
GCC uses full 512-bit register to return the constant from the function.
The patch avoid 512-bit register usage if "-mprefer-avx256" option used.

2017-09-28  Sergey Shalnov  <sergey.shal...@intel.com>

gcc/
        * config/i386/i386.md(*movsf_internal, *movdf_internal):
        Return 256-bit AVX modes for TARGET_PREFER_AVX256.

gcc/testsuite/
        * gcc.target/i386/avx512f-constant-float-return.c: New test.

0001-Avoid-useing-zmm-if-TARGET_PREFER_AVX256.patch
Description: 0001-Avoid-useing-zmm-if-TARGET_PREFER_AVX256.patch