[PATCH] D129876: [WIP][ConstantRange] Add support for multiply and left shift with nowrap flags

[Philip Reames via Phabricator via llvm-commits]

reames created this revision.
reames added reviewers: nikic, fhahn.
Herald added subscribers: javed.absar, bollu, hiraditya, mcrosier.
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This patch adds support for multiply and left shift variants which use NoWrap flags to restrict the range returned.  It directly follows the pattern already taken for add/sub, and extends it to mul/shl.

This is a WIP for two major reasons, both of which I'd appreciate some input on.

1. I don't understand the bits in add/sub about being required to return empty ranges on definite overflow.  I can see that from a precision perspective, but since both the 2s complement and saturating variants are valid implementations of the no-wrap behavior, it seems like intersecting them should always be valid.  Am I right here?  Or is my code subtly wrong?
2. Suggestions on how to test this?  I glanced at the ConstantRangeTest file, and am looking for specific guidance on which exhaustive test harness to use.  This file has gotten quite complicated.

Once complete, I plan to use this in SCEV to help refine the ranges returned for multiplies.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D129876

Files:
  llvm/include/llvm/IR/ConstantRange.h
  llvm/lib/IR/ConstantRange.cpp
  llvm/test/Transforms/CorrelatedValuePropagation/mul.ll
  llvm/test/Transforms/CorrelatedValuePropagation/shl.ll

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