[PATCH] D74066: [ValueTracking] usub(a, b) cannot overflow if a >= b.

[Florian Hahn via Phabricator via llvm-commits]

fhahn updated this revision to Diff 242840.
fhahn added a comment.

Updated to limit isImpliedByDomCond to usub.with.overflow calls for now.

In D74066#1859995 <https://reviews.llvm.org/D74066#1859995>, @nikic wrote:

> My only concern here is compile-time impact. Keep in mind that this function is not just being called for `usub.with.overflow`, but for every `sub` in the IR, trying to infer the `nuw` flag. As `isImpliedByDomCondition()` only inspects the direct predecessor, that's probably fine though.


Ah right! isImpliedByDomCondition should not be too expensive, but I've limited using it to usub.with.overflow for now.

> Generally we're missing a pass that can propagate conditions and assumes with non-constant operands (CVP mostly covers the constant operand case)...

Agreed!


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D74066/new/

https://reviews.llvm.org/D74066

Files:
  llvm/lib/Analysis/ValueTracking.cpp
  llvm/test/Transforms/InstCombine/usub-overflow-known-by-implied-cond.ll

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