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[ScalarEvolution] Strictly enforce pointer/int type rules.

Authored by efriedma on Jun 23 2021, 2:43 PM.

Description

[ScalarEvolution] Strictly enforce pointer/int type rules.

Rules:

  1. SCEVUnknown is a pointer if and only if the LLVM IR value is a pointer.
  2. SCEVPtrToInt is never a pointer.
  3. If any other SCEV expression has no pointer operands, the result is an integer.
  4. If a SCEVAddExpr has exactly one pointer operand, the result is a pointer.
  5. If a SCEVAddRecExpr's first operand is a pointer, and it has no other pointer operands, the result is a pointer.
  6. If every operand of a SCEVMinMaxExpr is a pointer, the result is a pointer.
  7. Otherwise, the SCEV expression is invalid.

I'm not sure how useful rule 6 is in practice. If we exclude it, we can
guarantee that ScalarEvolution::getPointerBase always returns a
SCEVUnknown, which might be a helpful property. Anyway, I'll leave that
for a followup.

This is basically mop-up at this point; all the changes with significant
functional effects have landed. Some of the remaining changes could be
split off, but I don't see much point.

Differential Revision: https://reviews.llvm.org/D105510