C++ StoreInst::getAllMetadata方法代码示例

/// \brief Combine stores to match the type of value being stored.
///
/// The core idea here is that the memory does not have any intrinsic type and
/// where we can we should match the type of a store to the type of value being
/// stored.
///
/// However, this routine must never change the width of a store or the number of
/// stores as that would introduce a semantic change. This combine is expected to
/// be a semantic no-op which just allows stores to more closely model the types
/// of their incoming values.
///
/// Currently, we also refuse to change the precise type used for an atomic or
/// volatile store. This is debatable, and might be reasonable to change later.
/// However, it is risky in case some backend or other part of LLVM is relying
/// on the exact type stored to select appropriate atomic operations.
///
/// \returns true if the store was successfully combined away. This indicates
/// the caller must erase the store instruction. We have to let the caller erase
/// the store instruction sas otherwise there is no way to signal whether it was
/// combined or not: IC.EraseInstFromFunction returns a null pointer.
static bool combineStoreToValueType(InstCombiner &IC, StoreInst &SI) {
  // FIXME: We could probably with some care handle both volatile and atomic
  // stores here but it isn't clear that this is important.
  if (!SI.isSimple())
    return false;

  Value *Ptr = SI.getPointerOperand();
  Value *V = SI.getValueOperand();
  unsigned AS = SI.getPointerAddressSpace();
  SmallVector<std::pair<unsigned, MDNode *>, 8> MD;
  SI.getAllMetadata(MD);

  // Fold away bit casts of the stored value by storing the original type.
  if (auto *BC = dyn_cast<BitCastInst>(V)) {
    V = BC->getOperand(0);
    StoreInst *NewStore = IC.Builder->CreateAlignedStore(
        V, IC.Builder->CreateBitCast(Ptr, V->getType()->getPointerTo(AS)),
        SI.getAlignment());
    for (const auto &MDPair : MD) {
      unsigned ID = MDPair.first;
      MDNode *N = MDPair.second;
      // Note, essentially every kind of metadata should be preserved here! This
      // routine is supposed to clone a store instruction changing *only its
      // type*. The only metadata it makes sense to drop is metadata which is
      // invalidated when the pointer type changes. This should essentially
      // never be the case in LLVM, but we explicitly switch over only known
      // metadata to be conservatively correct. If you are adding metadata to
      // LLVM which pertains to stores, you almost certainly want to add it
      // here.
      switch (ID) {
      case LLVMContext::MD_dbg:
      case LLVMContext::MD_tbaa:
      case LLVMContext::MD_prof:
      case LLVMContext::MD_fpmath:
      case LLVMContext::MD_tbaa_struct:
      case LLVMContext::MD_alias_scope:
      case LLVMContext::MD_noalias:
      case LLVMContext::MD_nontemporal:
      case LLVMContext::MD_mem_parallel_loop_access:
      case LLVMContext::MD_nonnull:
        // All of these directly apply.
        NewStore->setMetadata(ID, N);
        break;

      case LLVMContext::MD_invariant_load:
      case LLVMContext::MD_range:
        break;
      }
    }
    return true;
  }

  // FIXME: We should also canonicalize loads of vectors when their elements are
  // cast to other types.
  return false;
}