Apply some small reviewer suggestions

Author: jdenny-ornl

llvm/include/llvm/Transforms/Utils/LoopUtils.h

@@ -355,6 +355,14 @@ LLVM_ABI bool addStringMetadataToLoop(Loop *TheLoop, const char *MDString,
 /// TODO: Eventually, once all passes have migrated away from setting branch
 /// weights to indicate estimated trip counts, this function will drop the
 /// \p EstimatedLoopInvocationWeight parameter.
+///
+/// TODO: There are also passes that currently do not consider estimated trip
+/// counts at all but that, for example, affect whether trip counts can be
+/// estimated from branch weights.  Once all such passes have been adjusted to
+/// update this metadata, this function might stop estimating trip counts from
+/// branch weights and instead simply get the \c llvm.loop_estimated_trip_count
+/// metadata.  See also the \c llvm.loop.estimated_trip_count entry in
+/// \c LangRef.rst.
 LLVM_ABI std::optional<unsigned>
 getLoopEstimatedTripCount(Loop *L,
                           unsigned *EstimatedLoopInvocationWeight = nullptr,

llvm/lib/Transforms/Utils/LoopUtils.cpp

@@ -226,7 +226,7 @@ bool llvm::addStringMetadataToLoop(Loop *TheLoop, const char *StringMD,
       if (NumOps == 1 || NumOps == 2) {
         MDString *S = dyn_cast<MDString>(Node->getOperand(0));
         if (S && S->getString() == StringMD) {
-          // If it is already in place, do nothing.
+          // If the metadata and any value are already as specified, do nothing.
           if (NumOps == 2 && V) {
             ConstantInt *IntMD =
                 mdconst::extract_or_null<ConstantInt>(Node->getOperand(1));
@@ -879,7 +879,7 @@ std::optional<unsigned> llvm::getLoopEstimatedTripCount(
   // EstimatedLoopInvocationWeight parameter.
   if (EstimatedLoopInvocationWeight) {
     if (BranchInst *ExitingBranch = getExpectedExitLoopLatchBranch(L)) {
-      uint64_t LoopWeight, ExitWeight;
+      uint64_t LoopWeight = 0, ExitWeight = 0; // Inits expected to be unused.
       if (!extractBranchWeights(*ExitingBranch, LoopWeight, ExitWeight))
         return std::nullopt;
       if (L->contains(ExitingBranch->getSuccessor(1)))
@@ -951,7 +951,7 @@ bool llvm::setLoopEstimatedTripCount(
   unsigned LatchExitWeight = 0;
   unsigned BackedgeTakenWeight = 0;
 
-  if (*EstimatedTripCount > 0) {
+  if (*EstimatedTripCount != 0) {
     LatchExitWeight = *EstimatedloopInvocationWeight;
     BackedgeTakenWeight = (*EstimatedTripCount - 1) * LatchExitWeight;
   }