[AArch64] Remove an unnecessary restriction on pre-index instructions.

Previously, the index was constrained to the size of the memory operation for
no apparent reason.  This change removes that constraint so that we can form
pre-index instructions with any valid offset.

llvm-svn: 248931
diff --git a/llvm/lib/Target/AArch64/AArch64LoadStoreOptimizer.cpp b/llvm/lib/Target/AArch64/AArch64LoadStoreOptimizer.cpp
index 1e73328..de3930c 100644
--- a/llvm/lib/Target/AArch64/AArch64LoadStoreOptimizer.cpp
+++ b/llvm/lib/Target/AArch64/AArch64LoadStoreOptimizer.cpp
@@ -959,7 +959,6 @@
 
   unsigned BaseReg = getLdStBaseOp(MemMI).getReg();
   int Offset = getLdStOffsetOp(MemMI).getImm();
-  unsigned MemSize = getMemScale(MemMI);
 
   // If the load/store is the first instruction in the block, there's obviously
   // not any matching update. Ditto if the memory offset isn't zero.
@@ -991,7 +990,7 @@
     ++Count;
 
     // If we found a match, return it.
-    if (isMatchingUpdateInsn(I, MI, BaseReg, MemSize))
+    if (isMatchingUpdateInsn(I, MI, BaseReg, Offset))
       return MBBI;
 
     // Update the status of what the instruction clobbered and used.