[LoopRotate] Fix for dbg.value propagation

[samparker]

Summary

The patch of D30190 was reverted in r297159. This patch should address the bug raised in https://bugs.llvm.org/show_bug.cgi?id=32171 as well as a similar issue that Adrian had pointed out, but I missed, in the previous review.

[aprantl]

Inline comments, otherwise looks ok.

lib/Transforms/Scalar/LoopRotation.cpp

185

auto *

186

I think you still want a dyn_cast_or_null here. Optimizations sometimes delete an llvm::Value without deleting debug intrinsics pointing to it.

189

You could get rid of all curly braces here if you want to.

[samparker]

lib/Transforms/Scalar/LoopRotation.cpp

186

Yes, thank you!

[samparker]

submitted in r297269

lib/Transforms/Scalar/LoopRotation.cpp

 
 /// Propagate dbg.value intrinsics through the newly inserted Phis.
 static void insertDebugValues(BasicBlock *OrigHeader,
                               SmallVectorImpl<PHINode*> &InsertedPHIs) {
   ValueToValueMapTy DbgValueMap;
 
   // Map existing PHI nodes to their dbg.values.
   for (auto &I : *OrigHeader) {
     if (auto DbgII = dyn_cast<DbgInfoIntrinsic>(&I)) {
-      if (isa<PHINode>(DbgII->getVariableLocation()))
-        DbgValueMap.insert({DbgII->getVariableLocation(), DbgII});
+      if (auto Loc = dyn_cast<PHINode>(DbgII->getVariableLocation()))
+        DbgValueMap.insert({Loc, DbgII});
     }
   }
 
   // Then iterate through the new PHIs and look to see if they use one of the
   // previously mapped PHIs. If so, insert a new dbg.value intrinsic that will
   // propagate the info through the new PHI.
   LLVMContext &C = OrigHeader->getContext();
   for (auto PHI : InsertedPHIs) {
     for (auto VI : PHI->operand_values()) {
       auto V = DbgValueMap.find(VI);
       if (V != DbgValueMap.end()) {
-        auto *DbgII = dyn_cast<DbgInfoIntrinsic>(V->second);
+        auto *DbgII = cast<DbgInfoIntrinsic>(V->second);
         Instruction *NewDbgII = DbgII->clone();
         auto PhiMAV = MetadataAsValue::get(C, ValueAsMetadata::get(PHI));
         NewDbgII->setOperand(0, PhiMAV);
         BasicBlock *Parent = PHI->getParent();
         NewDbgII->insertBefore(Parent->getFirstNonPHIOrDbgOrLifetime());
       }
     }
   }