[AMDGPU] Prevent post-RA scheduler from breaking memory clauses

The pre-RA scheduler does load/store clustering, but post-RA
scheduler undoes it. Add mutation to prevent it.

Differential Revision: https://reviews.llvm.org/D38014

llvm-svn: 313670
diff --git a/llvm/test/CodeGen/AMDGPU/and.ll b/llvm/test/CodeGen/AMDGPU/and.ll
index ee01901..8693089 100644
--- a/llvm/test/CodeGen/AMDGPU/and.ll
+++ b/llvm/test/CodeGen/AMDGPU/and.ll
@@ -219,10 +219,10 @@
 }
 
 ; FUNC-LABEL: {{^}}s_and_multi_use_inline_imm_i64:
+; SI: s_load_dwordx2
 ; SI: s_load_dword [[A:s[0-9]+]]
 ; SI: s_load_dword [[B:s[0-9]+]]
 ; SI: s_load_dwordx2
-; SI: s_load_dwordx2
 ; SI-NOT: and
 ; SI: s_lshl_b32 [[A]], [[A]], 1
 ; SI: s_lshl_b32 [[B]], [[B]], 1