[Bug regression/67609] New: [Regression] Generates wrong code for SSE2 _mm_load_pd

[bisqwit at iki dot fi]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67609

            Bug ID: 67609
           Summary: [Regression] Generates wrong code for SSE2 _mm_load_pd
           Product: gcc
           Version: 5.2.1
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: regression
          Assignee: unassigned at gcc dot gnu.org
          Reporter: bisqwit at iki dot fi
  Target Milestone: ---

For this program (needs -msse2 to compile).

    #include <emmintrin.h>
    __m128d reg;
    void set_lower(double b)
    {
        double v[2];
        _mm_store_pd(v, reg);
        v[0] = b;
        reg = _mm_load_pd(v);
    }

On optimization levels -O1 and up, GCC 5.2 incorrectly generates code that
destroys the upper half of reg.
        movapd  %xmm0, %xmm1
        movaps  %xmm1, reg(%rip)

On -O0, the bug does not occur.
If the index expression is changed into an expression whose value is not known
at compile-time, the code will work properly.

GCC 4.9 does this correctly (if with bit too much labor):

        movdqa  reg(%rip), %xmm1
        movaps  %xmm1, -24(%rsp)
        movsd   %xmm0, -24(%rsp)
        movapd  -24(%rsp), %xmm2
        movaps  %xmm2, reg(%rip)

For comparison, Clang 3.4 and 3.5:
        movlpd  %xmm0, reg(%rip)

For comparison, Clang 3.6:
        movaps  reg(%rip), %xmm1
        movsd   %xmm0, %xmm1
        movaps  %xmm1, reg(%rip)