[Bug target/55941] New: [4.8 Regression] Strange copy of double (in struct) to stack

[glisse at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55941

             Bug #: 55941
           Summary: [4.8 Regression] Strange copy of double (in struct) to
                    stack
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: glisse@gcc.gnu.org
            Target: x86_64-linux-gnu


typedef struct A { double a, b; } A;
double f(A x,double y){return x.a+y;}

generates with gcc -Ofast -S:

    addsd    %xmm0, %xmm2
    movsd    %xmm0, -8(%rsp)
    movapd    %xmm2, %xmm0
    ret

I don't understand what that movsd is doing there?

Note that gcc-4.7 generates the expected:

    addsd    %xmm2, %xmm0
    ret