[PATCH] D60598: [ConstantRange] Clarify makeGuaranteedNoWrapRegion() guarantees

[Nikita Popov via Phabricator via llvm-commits]

nikic created this revision.
nikic added reviewers: lebedev.ri, spatel.
Herald added subscribers: llvm-commits, hiraditya.
Herald added a project: LLVM.

makeGuaranteedNoWrapRegion() is actually makeExactNoWrapRegion() as long as only one of NUW or NSW is specified. This is not obvious from the current documentation, and some code seems to think that it is only exact for single-element ranges. Clarify docs and add tests to be more confident this really holds.

There are currently no users of makeGuaranteedNoWrapRegion() that pass both NUW and NSW. I think it would be best to drop support for this entirely and then rename the function to makeExactNoWrapRegion().

Knowing that the no-wrap region is exact is useful, because we can backwards-constrain values. What I have in mind in particular is that LVI should be able to constrain values on edges where the with.overflow overflow flag is false.


Repository:
  rL LLVM

https://reviews.llvm.org/D60598

Files:
  llvm/include/llvm/IR/ConstantRange.h
  llvm/lib/IR/ConstantRange.cpp
  llvm/unittests/IR/ConstantRangeTest.cpp

-------------- next part --------------
A non-text attachment was scrubbed...
Name: D60598.194809.patch
Type: text/x-patch
Size: 4790 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20190412/c7538c3b/attachment.bin>