Notice about lack of SIMD support.

In some cases, when SIMD primitives are used without the -fllvm flag, instead of giving the friendly SIMD vector instructions require the LLVM back-end., GHC crashes with varying messages.

The simplest example is

{-# LANGUAGE MagicHash #-}
module Foo where
import GHC.Prim
data V = V Int8X16#

In 7.8.4 this crashes with

ghc: panic! (the 'impossible' happened)
  (GHC version 7.8.4 for x86_64-unknown-linux):
	Size.intSize W128

According to osa1, in HEAD this still crashes, but with

ghc-stage2: panic! (the 'impossible' happened)
  (GHC version 7.11.20150717 for x86_64-unknown-linux):
        Format.intFormat W128

Trac metadata

Trac field	Value
Version	7.8.4
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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