Check size on transformer cache

Related: marian-nmt#881

Author: graemenail

src/models/transformer.h

@@ -290,7 +290,7 @@ class Transformer : public EncoderOrDecoderBase {
     // memoization propagation (short-term)
     if (cache                                                                          // if caching
         && cache_.count(prefix + "_keys") > 0                                          // and the keys expression has been seen
-        && cache_[prefix + "_keys"]->shape().elements() == keys->shape().elements()) { // and the underlying element size did not change
+        && cache_[prefix + "_keys"]->shape() == keys->shape()) {                       // and the underlying shape did not change
       kh = cache_[prefix + "_keys"];                                                   // then return cached tensor
     }
     else {
@@ -306,7 +306,7 @@ class Transformer : public EncoderOrDecoderBase {
     Expr vh;
     if (cache 
         && cache_.count(prefix + "_values") > 0 
-        && cache_[prefix + "_values"]->shape().elements() == values->shape().elements()) {
+        && cache_[prefix + "_values"]->shape() == values->shape()) {
       vh = cache_[prefix + "_values"];
     } else {
       int dimValues = values->shape()[-1]; // different than dimModel when using lemma and factors combined with concatenation