SIL: fix the hash function for Projection

The hash function didn't take the "index" of an projection into account. This lead to quadratic behavior in redundant load elimination and dead store elimination when compiling very large functions with many loads and stores.

rdar://problem/56268570

Author: eeckstein

include/swift/SIL/Projection.h

@@ -255,6 +255,8 @@ class Projection {
   unsigned getIndex() const {
     return Value.getIndex();
   }
+  
+  unsigned getHash() const { return (unsigned)Value.getStorage(); }
 
   /// Determine if I is a value projection instruction whose corresponding
   /// projection equals this projection.
@@ -689,7 +691,7 @@ static inline llvm::hash_code hash_value(const ProjectionPath &P) {
 
 /// Returns the hashcode for the projection path.
 static inline llvm::hash_code hash_value(const Projection &P) {
-  return llvm::hash_combine(static_cast<unsigned>(P.getKind()));
+  return llvm::hash_combine(P.getHash());
 }
 
 class ProjectionTree;