Refactor tree hashing (#861)

* Pre-allocated tree hash caches

* Add SmallVec to tree hash cache

* Avoid allocation for validator.pubkey

* Avoid iterator which seems to be doing heap alloc

* Add more smallvecs

* MOAR SMALLVEC

* Move non-test code to Hash256 tree hash

* Fix byte ordering error

* Add incomplete but working merkle stream impl

* Fix zero hash error

* Add zero hash fn

* Add MerkleStream comments

* Add smallvec, tidy

* Integrate into tree hash derive

* Update ssz_types tree hash

* Don't heap alloc for mix in length

* Add byte-level streaming to MerkleStream

* Avoid recursion in write method

* Update BLS to MerkleStream

* Fix some not-compiling tests

* Remove debug profiling

* Remove code duplication

* Move beacon state tree hash to new hasher

* Fix failing tests

* Update comments

* Add some fast-paths to tree_hash::merkle_root

* Remove unncessary test

* Rename MerkleStream -> MerkleHasher

* Rename new_with_leaf_count -> with_leaves

* Tidy

* Remove NonZeroUsize

* Remove todo

* Update smallvec

eth2/state_processing/src/per_block_processing/block_processing_builder.rs

@@ -50,9 +50,7 @@ impl<T: EthSpec> BlockProcessingBuilder<T> {
 
         match previous_block_root {
             Some(root) => builder.set_parent_root(root),
-            None => builder.set_parent_root(Hash256::from_slice(
-                &state.latest_block_header.tree_hash_root(),
-            )),
+            None => builder.set_parent_root(state.latest_block_header.tree_hash_root()),
         }
 
         let proposer_index = state.get_beacon_proposer_index(state.slot, spec).unwrap();
@@ -92,9 +90,7 @@ impl<T: EthSpec> BlockProcessingBuilder<T> {
 
         match previous_block_root {
             Some(root) => builder.set_parent_root(root),
-            None => builder.set_parent_root(Hash256::from_slice(
-                &state.latest_block_header.tree_hash_root(),
-            )),
+            None => builder.set_parent_root(state.latest_block_header.tree_hash_root()),
         }
 
         let proposer_index = state.get_beacon_proposer_index(state.slot, spec).unwrap();
@@ -149,9 +145,7 @@ impl<T: EthSpec> BlockProcessingBuilder<T> {
 
         match previous_block_root {
             Some(root) => builder.set_parent_root(root),
-            None => builder.set_parent_root(Hash256::from_slice(
-                &state.latest_block_header.tree_hash_root(),
-            )),
+            None => builder.set_parent_root(state.latest_block_header.tree_hash_root()),
         }
 
         let proposer_index = state.get_beacon_proposer_index(state.slot, spec).unwrap();
@@ -192,9 +186,7 @@ impl<T: EthSpec> BlockProcessingBuilder<T> {
 
         match previous_block_root {
             Some(root) => builder.set_parent_root(root),
-            None => builder.set_parent_root(Hash256::from_slice(
-                &state.latest_block_header.tree_hash_root(),
-            )),
+            None => builder.set_parent_root(state.latest_block_header.tree_hash_root()),
         }
 
         let proposer_index = state.get_beacon_proposer_index(state.slot, spec).unwrap();
@@ -241,9 +233,7 @@ impl<T: EthSpec> BlockProcessingBuilder<T> {
 
         match previous_block_root {
             Some(root) => builder.set_parent_root(root),
-            None => builder.set_parent_root(Hash256::from_slice(
-                &state.latest_block_header.tree_hash_root(),
-            )),
+            None => builder.set_parent_root(state.latest_block_header.tree_hash_root()),
         }
 
         let proposer_index = state.get_beacon_proposer_index(state.slot, spec).unwrap();
@@ -283,9 +273,7 @@ impl<T: EthSpec> BlockProcessingBuilder<T> {
 
         match previous_block_root {
             Some(root) => builder.set_parent_root(root),
-            None => builder.set_parent_root(Hash256::from_slice(
-                &state.latest_block_header.tree_hash_root(),
-            )),
+            None => builder.set_parent_root(state.latest_block_header.tree_hash_root()),
         }
 
         let proposer_index = state.get_beacon_proposer_index(state.slot, spec).unwrap();

eth2/state_processing/src/per_block_processing/signature_sets.rs

@@ -62,13 +62,13 @@ pub fn block_proposal_signature_set<'a, T: EthSpec>(
         }
         .tree_hash_root()
     } else {
-        block.signing_root(domain).as_bytes().to_vec()
+        block.signing_root(domain)
     };
 
     Ok(SignatureSet::single(
         &signed_block.signature,
         validator_pubkey(state, proposer_index)?,
-        message,
+        message.as_bytes().to_vec(),
     ))
 }
 

eth2/state_processing/src/per_block_processing/verify_deposit.rs

@@ -57,7 +57,7 @@ pub fn verify_deposit_merkle_proof<T: EthSpec>(
 
     verify!(
         verify_merkle_proof(
-            Hash256::from_slice(&leaf),
+            leaf,
             &deposit.proof[..],
             spec.deposit_contract_tree_depth as usize + 1,
             deposit_index as usize,