Resurrect the assertion removed by r227717

[jingyue]

Summary

MSVC can compile "LoopID->getOperand(0) == LoopID" when LoopID is MDNode*.

[mkuper]

LGTM

(So what was the problem, the constness?)

[jingyue]

I suspect the issue you saw is a bug in MSVC. There is a path from MDOperand & to const MDNode *. http://llvm.org/docs/doxygen/html/Metadata_8h_source.html#l00547 defines a type caster from MDOperand & to Metadata *, Metadata is a super class of MDNode, and finally changing constness is a valid implicit cast.

Anyhow, I noticed Loop::getLoopID() returns MDNode * instead of const MDNode *, and using MDNode * seems to work for MSVC. Therefore, I took this approach. Did you confirm it does fix the building error on your end?

[mkuper]

Yes, I've confirmed this builds for me..

llvm/trunk/include/llvm/Transforms/Utils/UnrollLoop.h

 
 bool UnrollLoop(Loop *L, unsigned Count, unsigned TripCount, bool AllowRuntime,
                 unsigned TripMultiple, LoopInfo *LI, Pass *PP,
                 LPPassManager *LPM, AssumptionCache *AC);
 
 bool UnrollRuntimeLoopProlog(Loop *L, unsigned Count, LoopInfo *LI,
                              LPPassManager* LPM);
 
-const MDNode *GetUnrollMetadata(const MDNode *LoopID, StringRef Name);
+MDNode *GetUnrollMetadata(MDNode *LoopID, StringRef Name);
 }
 
 #endif

llvm/trunk/lib/Target/NVPTX/NVPTXAsmPrinter.cpp

bool NVPTXAsmPrinter::isLoopHeaderOfNoUnroll(
   // whether its metadata contains llvm.loop.unroll.disable.
   for (auto I = MBB.pred_begin(); I != MBB.pred_end(); ++I) {
     const MachineBasicBlock *PMBB = *I;
     if (LI.getLoopFor(PMBB) != LI.getLoopFor(&MBB)) {
       // Edges from other loops to MBB are not back edges.
       continue;
     }
     if (const BasicBlock *PBB = PMBB->getBasicBlock()) {
-      if (const MDNode *LoopID =
-              PBB->getTerminator()->getMetadata("llvm.loop")) {
+      if (MDNode *LoopID = PBB->getTerminator()->getMetadata("llvm.loop")) {
         if (GetUnrollMetadata(LoopID, "llvm.loop.unroll.disable"))
           return true;
       }
     }
   }
   return false;
 }
 

llvm/trunk/lib/Transforms/Scalar/LoopUnrollPass.cpp

static unsigned ApproximateLoopSize(const Loop *L, unsigned &NumCalls,
   LoopSize = std::max(LoopSize, 3u);
 
   return LoopSize;
 }
 
 // Returns the loop hint metadata node with the given name (for example,
 // "llvm.loop.unroll.count").  If no such metadata node exists, then nullptr is
 // returned.
-static const MDNode *GetUnrollMetadataForLoop(const Loop *L, StringRef Name) {
-  MDNode *LoopID = L->getLoopID();
-  if (!LoopID)
-    return nullptr;
+static MDNode *GetUnrollMetadataForLoop(const Loop *L, StringRef Name) {
+  if (MDNode *LoopID = L->getLoopID())
     return GetUnrollMetadata(LoopID, Name);
+  return nullptr;
 }
 
 // Returns true if the loop has an unroll(full) pragma.
 static bool HasUnrollFullPragma(const Loop *L) {
   return GetUnrollMetadataForLoop(L, "llvm.loop.unroll.full");
 }
 
 // Returns true if the loop has an unroll(disable) pragma.
 static bool HasUnrollDisablePragma(const Loop *L) {
   return GetUnrollMetadataForLoop(L, "llvm.loop.unroll.disable");
 }
 
 // If loop has an unroll_count pragma return the (necessarily
 // positive) value from the pragma.  Otherwise return 0.
 static unsigned UnrollCountPragmaValue(const Loop *L) {
-  const MDNode *MD = GetUnrollMetadataForLoop(L, "llvm.loop.unroll.count");
+  MDNode *MD = GetUnrollMetadataForLoop(L, "llvm.loop.unroll.count");
   if (MD) {
     assert(MD->getNumOperands() == 2 &&
            "Unroll count hint metadata should have two operands.");
     unsigned Count =
         mdconst::extract<ConstantInt>(MD->getOperand(1))->getZExtValue();
     assert(Count >= 1 && "Unroll count must be positive.");
     return Count;
   }

llvm/trunk/lib/Transforms/Utils/LoopUnroll.cpp

bool llvm::UnrollLoop(Loop *L, unsigned Count, unsigned TripCount,
   }
 
   return true;
 }
 
 /// Given an llvm.loop loop id metadata node, returns the loop hint metadata
 /// node with the given name (for example, "llvm.loop.unroll.count"). If no
 /// such metadata node exists, then nullptr is returned.
-const MDNode *llvm::GetUnrollMetadata(const MDNode *LoopID, StringRef Name) {
+MDNode *llvm::GetUnrollMetadata(MDNode *LoopID, StringRef Name) {
   // First operand should refer to the loop id itself.
   assert(LoopID->getNumOperands() > 0 && "requires at least one operand");
+  assert(LoopID->getOperand(0) == LoopID && "invalid loop id");
 
   for (unsigned i = 1, e = LoopID->getNumOperands(); i < e; ++i) {
-    const MDNode *MD = dyn_cast<MDNode>(LoopID->getOperand(i));
+    MDNode *MD = dyn_cast<MDNode>(LoopID->getOperand(i));
     if (!MD)
       continue;
 
-    const MDString *S = dyn_cast<MDString>(MD->getOperand(0));
+    MDString *S = dyn_cast<MDString>(MD->getOperand(0));
     if (!S)
       continue;
 
     if (Name.equals(S->getString()))
       return MD;
   }
   return nullptr;
 }