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

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Summary

This path fixes the following warnings that were reported while
running Clang Static Analyzer on Clang code base:

Logic error: called C++ object pointer is null, on files

• lib/Target/Hexagon/RDFGraph.cpp
• lib/Target/Hexagon/HexagonCFGOptimizer.cpp.

Logic error: branch condition evaluates to a garbage value, on file:

• lib/Target/Hexagon/HexagonInstrInfo.cpp.

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

[kparzysz]

LGTM. I added a minor comment, but it's not a blocker.

lib/Target/Hexagon/HexagonInstrInfo.cpp

1304

The array OpCExtended is initialized in the loop below (line 1308).

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lib/Target/Hexagon/HexagonInstrInfo.cpp

1304

This one was added to suppress a warning in the following case:

1305. ​ if (NumOperands > 4)
1306. ​ NumOperands = 4;
1307. ​
1308. ​ for (int i = 0; i < NumOperands; i++)
1309. ​ OpCExtended[i] = (isOperandExtended(&MI, i) && isConstExtended(&MI));
1310. ​​ switch(Opc) {

...

1361. ​ case Hexagon::S4_storeiri_io:
1362. return (OpCExtended[1] || isUInt<6>(MI.getOperand(1).getImm())) &&
1363. (OpCExtended[2] || isInt<6>(MI.getOperand(2).getImm()));

...

1375. }

If branches at lines 1305 and 1308 evaluate to 'false', then the branch condition at line 1362 would evaluate to a garbage value because OpCExtended wasn't initialized.

If this is OK for you, then I would need your help to commit this for me as I do not have commit access.

Thanks.

[kparzysz]

lib/Target/Hexagon/HexagonInstrInfo.cpp

1304

NumOperands is the number of operands in the instruction. S4_storeiri_io has 3, so NumOperands will be 3. The loop at 1308-1309 will initialize OpCExtended for i=0..2, so both references will be valid.

lib/Target/Hexagon/HexagonCFGOptimizer.cpp

if (MII != MBB->end()) {
           continue;
         }
 
         if ((NumSuccs == 2) && LayoutSucc && (LayoutSucc->pred_size() == 1)) {
 
           // Ensure that BB2 has one instruction -- an unconditional jump.
           if ((LayoutSucc->size() == 1) &&
               IsUnconditionalJump(LayoutSucc->front().getOpcode())) {
+            assert(JumpAroundTarget && "jump target is needed to process second basic block");
             MachineBasicBlock* UncondTarget =
               LayoutSucc->front().getOperand(0).getMBB();
             // Check if the layout successor of BB2 is BB3.
             bool case1 = LayoutSucc->isLayoutSuccessor(JumpAroundTarget);
             bool case2 = JumpAroundTarget->isSuccessor(UncondTarget) &&
               JumpAroundTarget->size() >= 1 &&
               IsUnconditionalJump(JumpAroundTarget->back().getOpcode()) &&
               JumpAroundTarget->pred_size() == 1 &&

lib/Target/Hexagon/HexagonInstrInfo.cpp

bool HexagonInstrInfo::isPredicable(MachineInstr &MI) const {
   if (!isPred)
     return false;
 
   const int Opc = MI.getOpcode();
   int NumOperands = MI.getNumOperands();
 
   // Keep a flag for upto 4 operands in the instructions, to indicate if
   // that operand has been constant extended.
-  bool OpCExtended[4];
+  bool OpCExtended[4] = {false};
   if (NumOperands > 4)
     NumOperands = 4;
 
   for (int i = 0; i < NumOperands; i++)
     OpCExtended[i] = (isOperandExtended(&MI, i) && isConstExtended(&MI));
 
   switch(Opc) {
   case Hexagon::A2_tfrsi:

lib/Target/Hexagon/RDFGraph.cpp

 }
 
 // Create data-flow links for all instructions in the block node BA. This
 // will include updating any phi nodes in BA.
 void DataFlowGraph::linkBlockRefs(DefStackMap &DefM, NodeAddr<BlockNode*> BA) {
   // Push block delimiters.
   markBlock(BA.Id, DefM);
 
+  assert(BA.Addr && "block node address is needed to create a data-flow link");
   // For each non-phi instruction in the block, link all the defs and uses
   // to their reaching defs. For any member of the block (including phis),
   // push the defs on the corresponding stacks.
   for (NodeAddr<InstrNode*> IA : BA.Addr->members(*this)) {
     // Ignore phi nodes here. They will be linked part by part from the
     // predecessors.
     if (IA.Addr->getKind() == NodeAttrs::Stmt)
       linkStmtRefs(DefM, IA);