[scan-build] fix warnings emitted on LLVM CodeGen 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 files:

• lib/CodeGen/AsmPrinter/DwarfUnit.cpp,
• lib/CodeGen/ScheduleDAGInstrs.cpp,
• lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp.

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

[jlebar]

lgtm for NVPTX changes.

[apelete]

Ping :).
Can someone help this one find its way into he main repo ?

[apelete]

[clang-analyzer] fix warnings emitted on llvm code base

Changes since last revision:

• lib/Transforms/Vectorize/SLPVectorizer.cpp: rework the fix for the warning in BoUpSLP::optimizeGatherSequence() and fix another one in BoUpSLP::BlockScheduling::tryScheduleBundle(),

• lib/Analysis/LoopInfo.cpp: rework the fix in UnloopUpdater::getNearestLoop().

[apelete]

[clang-analyzer] fix warnings emitted on llvm code base

Changes since last revision:

• fast forward rebase on git master branch.

[apelete]

Waiting for review, could someone please have a look at this one ?

[apelete]

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

Changes since last revision:

• split patch into CodeGen changes unit to ease review process,
• cherry-pick CodeGen changes from D19498.

[MatzeB]

LGTM

lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

6469

... "must not be NULL"

lib/CodeGen/AsmPrinter/DwarfUnit.cpp

for (unsigned i = 0, N = Fields.size(); i < N; ++i) {
     auto *DT = cast<DIDerivedType>(Fields[i]);
     StringRef fieldName = DT->getName();
     if (fieldName == "__forwarding")
       forwardingField = DT;
     else if (fieldName == varName)
       varField = DT;
   }
 
+  assert(forwardingField && "forwarding field must not be NULL");
+  assert(varField && "var field must not be NULL");
+
   // Get the offsets for the forwarding field and the variable field.
   unsigned forwardingFieldOffset = forwardingField->getOffsetInBits() >> 3;
   unsigned varFieldOffset = varField->getOffsetInBits() >> 2;
 
   // Decode the original location, and use that as the start of the byref
   // variable's location.
   DIELoc *Loc = new (DIEValueAllocator) DIELoc;
 

lib/CodeGen/ScheduleDAGInstrs.cpp

void ScheduleDAGInstrs::buildSchedGraph(AliasAnalysis *AA,
   // ExitSU.
   addSchedBarrierDeps();
 
   // Walk the list of instructions, from bottom moving up.
   MachineInstr *DbgMI = nullptr;
   for (MachineBasicBlock::iterator MII = RegionEnd, MIE = RegionBegin;
        MII != MIE; --MII) {
     MachineInstr *MI = std::prev(MII);
-    if (MI && DbgMI) {
+
+    if (DbgMI) {
       DbgValues.push_back(std::make_pair(DbgMI, MI));
       DbgMI = nullptr;
     }
 
     if (MI->isDebugValue()) {
       DbgMI = MI;
       continue;
     }

lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp

static void GetRegistersForValue(SelectionDAG &DAG,
 
   MVT RegVT;
   EVT ValueVT = OpInfo.ConstraintVT;
 
   // If this is a constraint for a specific physical register, like {r17},
   // assign it now.
   if (unsigned AssignedReg = PhysReg.first) {
     const TargetRegisterClass *RC = PhysReg.second;
+
+    assert(RC && "TargetRegisterClass needs to be not NULL");
+
     if (OpInfo.ConstraintVT == MVT::Other)
       ValueVT = *RC->vt_begin();
 
     // Get the actual register value type.  This is important, because the user
     // may have asked for (e.g.) the AX register in i32 type.  We need to
     // remember that AX is actually i16 to get the right extension.
     RegVT = *RC->vt_begin();