INSERTPS can select any element from src and insert into any place
of the dest.  For SSE4.1 targets, compiler can generate e.g.

    insertps $64, %xmm0, %xmm1

to insert element 1 from %xmm1 to element 0 of %xmm0.

gcc/ChangeLog:

    PR target/94908
    * config/i386/i386-builtin.def (__builtin_ia32_insertps128):
    Use CODE_FOR_sse4_1_insertps_v4sf.
    * config/i386/i386-expand.cc (expand_vec_perm_insertps): New.
    (expand_vec_perm_1): Call expand_vec_per_insertps.
    * config/i386/i386.md ("unspec"): Declare UNSPEC_INSERTPS here.
    * config/i386/mmx.md (mmxscalarmode): New mode attribute.
    (@sse4_1_insertps_<mode>): New insn pattern.
    * config/i386/sse.md (@sse4_1_insertps_<mode>): Macroize insn
    pattern from sse4_1_insertps using VI4F_128 mode iterator.

gcc/testsuite/ChangeLog:

    PR target/94908
    * gcc.target/i386/pr94908.c: New test.
    * gcc.target/i386/sse4_1-insertps-5.c: New test.
    * gcc.target/i386/vperm-v4sf-2-sse4.c: New test.

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

Pushed to master.

Uros.