[Bug c/79678] New: x86 (and other?) SIMD builtins have signedness issues

[jbeulich at novell dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79678

            Bug ID: 79678
           Summary: x86 (and other?) SIMD builtins have signedness issues
           Product: gcc
           Version: 6.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jbeulich at novell dot com
  Target Milestone: ---

At least builtins clearly acting on and/or returning packed unsigned data
should have parameter/return types derived from unsigned ones. Beside requiring
needless casts, even trivial things like "__builtin_ia32_pmaxub128() > 0"
otherwise produce wrong code.

Similarly builtins acting on signed 8-bit quantities should not have
parameter/return types derived from plain char.