SILoadStoreOptimizer.cpp: Fix a warning in r279991. [-Wunused-variable]

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@280075 91177308-0d34-0410-b5e6-96231b3b80d8

Author: chapuni

lib/Target/AMDGPU/SILoadStoreOptimizer.cpp

@@ -336,6 +336,7 @@ MachineBasicBlock::iterator  SILoadStoreOptimizer::mergeRead2Pair(
     .addImm(0) // gds
     .addMemOperand(*I->memoperands_begin())
     .addMemOperand(*Paired->memoperands_begin());
+  (void)Read2;
 
   const MCInstrDesc &CopyDesc = TII->get(TargetOpcode::COPY);