[PATCH] D42123: Derive GEP index type from Data Layout

[Ayal Zaks via Phabricator via llvm-commits]

Ayal added inline comments.


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Comment at: ../lib/Analysis/ScalarEvolution.cpp:3675
   assert(isSCEVable(Ty) && "Type is not SCEVable!");
+  if (Ty->isPointerTy())
+    return getDataLayout().getIndexTypeSizeInBits(Ty);
----------------
delena wrote:
> sanjoy wrote:
> > I don't think this is a correct place to make this change -- the size of a pointer is the size of a pointer.  I think you need to change the SCEV corresponding to GEP(Ptr, Idx) to be "sext(Ptr) + Idx" or "Ptr + sext(Idx)" depending on their relative sizes.
> I can't create SCEV expressions with ptr+ind, it will fail with assertion on different types.
Elena, Sanjoy's thought above to change SCEV to be "sext(Ptr) + Idx" or "Ptr + sext(Idx)" will bring the two addends to be of the same type, i.e., of the larger type. The challenge in your case is lack of target support for integer addition of pointer-sized integers; which seems similar to CHERI's case. Except CHERI pointers (or capabilities) hold in addition to a standard-sized address additional information, such that the latter can be stripped out for SCEV purposes (IIUC - @theraven please correct if needed); whereas in your case the address itself is larger than a standard-sized integer. Perhaps for your case too the pointer can be stripped down to standard-sized integers to leverage SCEV's capabilities on "legal" types, which seems to be what your patch is doing, coupled with separate logic that deals with the stripped out bits(?).


Repository:
  rL LLVM

https://reviews.llvm.org/D42123