[scan-build] fix warnings emitted on LLVM NVPTX code base

[apelete]

Summary

Fix logic error warnings of the type "called C++ object pointer is
null" emitted by Clang Static Analyzer on the following file:

lib/Target/NVPTX/NVPTXInstrInfo.cpp.

Signed-off-by: Apelete Seketeli <[e-mail]>

lib/Target/NVPTX/NVPTXInstrInfo.cpp

bool NVPTXInstrInfo::AnalyzeBranch(
   // Get the instruction before it if it's a terminator.
   MachineInstr *SecondLastInst = I;
 
   // If there are three terminators, we don't know what sort of block this is.
   if (SecondLastInst && I != MBB.begin() && isUnpredicatedTerminator(*--I))
     return true;
 
   // If the block ends with NVPTX::GOTO and NVPTX:CBranch, handle it.
-  if (SecondLastInst->getOpcode() == NVPTX::CBranch &&
+  if (SecondLastInst && SecondLastInst->getOpcode() == NVPTX::CBranch &&
       LastInst->getOpcode() == NVPTX::GOTO) {
     TBB = SecondLastInst->getOperand(1).getMBB();
     Cond.push_back(SecondLastInst->getOperand(0));
     FBB = LastInst->getOperand(0).getMBB();
     return false;
   }
 
   // If the block ends with two NVPTX:GOTOs, handle it.  The second one is not
   // executed, so remove it.
-  if (SecondLastInst->getOpcode() == NVPTX::GOTO &&
+  if (SecondLastInst && SecondLastInst->getOpcode() == NVPTX::GOTO &&
       LastInst->getOpcode() == NVPTX::GOTO) {
     TBB = SecondLastInst->getOperand(0).getMBB();
     I = LastInst;
     if (AllowModify)
       I->eraseFromParent();
     return false;
   }