[ARM][ParallelDSP] Disable for big-endian

Bail early when we don't have a preheader and also if the target is
big endian because it's written with only little endian in mind!

Differential Revision: https://reviews.llvm.org/D59368

llvm-svn: 356243
diff --git a/llvm/test/CodeGen/ARM/ParallelDSP/smlad0.ll b/llvm/test/CodeGen/ARM/ParallelDSP/smlad0.ll
index d3bf51f..acd694f 100644
--- a/llvm/test/CodeGen/ARM/ParallelDSP/smlad0.ll
+++ b/llvm/test/CodeGen/ARM/ParallelDSP/smlad0.ll
@@ -1,4 +1,5 @@
 ; RUN: opt -mtriple=arm-arm-eabi -mcpu=cortex-m33 < %s -arm-parallel-dsp -S | FileCheck %s
+; RUN: opt -mtriple=armeb-arm-eabi -mcpu=cortex-m0 < %s -arm-parallel-dsp -S | FileCheck %s --check-prefix=CHECK-UNSUPPORTED
 ;
 ; The Cortex-M0 does not support unaligned accesses:
 ; RUN: opt -mtriple=arm-arm-eabi -mcpu=cortex-m0 < %s -arm-parallel-dsp -S | FileCheck %s --check-prefix=CHECK-UNSUPPORTED