/// \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; }