Use AccessPath in LICM.

The LICM algorithm was not robust with respect to address projection
because it identifies a projected address by its SILValue. This should
never be done! Use AccessPath instead.

Fixes regressions caused by rdar://66791257 (Print statement provokes
"Can't unsafeBitCast between types of different sizes" when
optimizations enabled)

Author: atrick

include/swift/SIL/LoopInfo.h

@@ -60,6 +60,8 @@ class SILLoop : public llvm::LoopBase<SILBasicBlock, SILLoop> {
     }
   }
 
+  SILFunction *getFunction() const { return getHeader()->getParent(); }
+
 private:
   friend class llvm::LoopInfoBase<SILBasicBlock, SILLoop>;