[gardening] Be more defensive around a potentially uninitialized Store by initializing it to nullptr and asserting that it is not nullptr (i.e. was assigned) before using it.

Author: gottesmm

lib/SILOptimizer/IPO/GlobalOpt.cpp

@@ -567,7 +567,7 @@ static SILFunction *genGetterFromInit(SILOptFunctionBuilder &FunctionBuilder,
   // Find the store instruction
   auto *BB = GetterF->getEntryBlock();
   SILValue Val;
-  SILInstruction *Store;
+  SILInstruction *Store = nullptr;
   for (auto II = BB->begin(), E = BB->end(); II != E;) {
     auto &I = *II++;
     if (isa<AllocGlobalInst>(&I)) {
@@ -586,6 +586,7 @@ static SILFunction *genGetterFromInit(SILOptFunctionBuilder &FunctionBuilder,
       B.createReturn(RI->getLoc(), Val);
       eraseUsesOfInstruction(RI);
       recursivelyDeleteTriviallyDeadInstructions(RI, true);
+      assert(Store && "Did not find a store?!");
       recursivelyDeleteTriviallyDeadInstructions(Store, true);
       return GetterF;
     }

lib/SILOptimizer/SILCombiner/SILCombinerCastVisitors.cpp

@@ -164,11 +164,13 @@ visitPointerToAddressInst(PointerToAddressInst *PTAI) {
   //   %addr = pointer_to_address %ptr, [strict] $T
   //   %result = index_addr %addr, %distance
   //
-  BuiltinInst *Bytes;
+  BuiltinInst *Bytes = nullptr;
   if (match(PTAI->getOperand(),
             m_IndexRawPointerInst(
                 m_ValueBase(),
                 m_TupleExtractOperation(m_BuiltinInst(Bytes), 0)))) {
+    assert(Bytes != nullptr &&
+           "Bytes should have been assigned a non-null value");
     if (match(Bytes, m_ApplyInst(BuiltinValueKind::SMulOver, m_ValueBase(),
                                  m_ApplyInst(BuiltinValueKind::Strideof,
                                              m_MetatypeInst(Metatype)),