[Bug target/68163] New: GCC on power8 does not issue the stxsspx instruction on power8

["meissner at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=68163

            Bug ID: 68163
           Summary: GCC on power8 does not issue the stxsspx instruction
                    on power8
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: target
          Assignee: unassigned at gcc dot gnu.org
          Reporter: meissner at gcc dot gnu.org
  Target Milestone: ---

Created attachment 36624
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=36624&action=edit
Sample program to show the problem.

If you select -mcpu=power8, and create a program that has more than 32 live
single precision values, the compiler will not use the stxsspx instruction to
store values in the Altivec registers.  Instead it will do a xscvdpspn
instruction to convert the internal format to vector form, then a mfvsrd
instruction to move the value into a GPR, and finally stw instruction to store
the 32-bit word.

If you change the type from float to double, generating the stxsdx instruction.