Add an assert for hasLoopInvariantOperands

[trentxintong]

Summary

Add an assert for hasLoopInvariantOperands

[sanjoy]

lib/Transforms/Scalar/LoopSink.cpp

288

I'd say something about the preheader in the assertion message: "Instructions in a loop's preheader should have loop invariant operands!" or something like that.

[trentxintong]

Address comments.

lib/Transforms/Scalar/LoopSink.cpp

std::stable_sort(ColdLoopBBs.begin(), ColdLoopBBs.end(),
                      return BFI.getBlockFreq(A) < BFI.getBlockFreq(B);
                    });
 
   // Traverse preheader's instructions in reverse order becaue if A depends
   // on B (A appears after B), A needs to be sinked first before B can be
   // sinked.
   for (auto II = Preheader->rbegin(), E = Preheader->rend(); II != E;) {
     Instruction *I = &*II++;
+    // No need to check for instruction's operands are loop invariant.
+    assert(L.hasLoopInvariantOperands(I) &&
+           "Insts in a loop's preheader should have loop invariant operands!");
     if (!canSinkOrHoistInst(*I, &AA, &DT, &L, &CurAST, nullptr))
       continue;
     if (sinkInstruction(L, *I, ColdLoopBBs, LoopBlockNumber, LI, DT, BFI))
       Changed = true;
   }
 
   if (Changed && SE)
     SE->forgetLoopDispositions(&L);