[PATCH] D16116: Refactor ValueTracking isDereferenceableAndAlignedPointer

[Artur Pilipenko via llvm-commits]

apilipenko created this revision.
apilipenko added reviewers: hfinkel, reames.
apilipenko added a subscriber: llvm-commits.

Current implementation of isDereferenceableAndAlignedPointer is messy. It tries to handle sized/non-sized types, looking through casts/relocations and inherent value dereferenceability properties in a single recursive function. Recent addition of alignment handling and context-sensitive non-null analysis made it even worse. This patch is an attempt to clean it up.

Inherent value dereferenceability properties are now handled in Value class:
* Value::isDereferenceablePointer
* Value::getDereferenceableBytes

The code which tracks dereferencability over a chain of values remains in ValueTracking. isDereferenceableAndAlignedPointer is no longer recursive. Instead it uses helper functions to strip all the casts/compute a base pointer and offset. 

Overall structure of this code is as follows:
* Try to determine if a value is dereferenceable without dealing with type sizes.
Strip type safe transformations only: address space casts, global aliases, GC relocations. If the resulting pointer is fully dereferenceable we are done. It will handle derferencability of opaque types.

* If the accessed type is sized try to decompose the value to a base pointer and an offset. Check if the accessed value lies within dereferenceable portion of the base pointer.

http://reviews.llvm.org/D16116

Files:
  include/llvm/Analysis/ValueTracking.h
  include/llvm/IR/Value.h
  lib/Analysis/ValueTracking.cpp
  lib/IR/Value.cpp

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