[PATCH] D71660: [ValueTracking] isKnownNonZero() should take non-null-ness assumptions into consideration (PR43267)

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri created this revision.
lebedev.ri added reviewers: spatel, jdoerfert, nikic, craig.topper.
lebedev.ri added a project: LLVM.
Herald added a subscriber: hiraditya.

It is pretty common to assume that something is not zero.
Even optimizer itself sometimes emits such assumptions
(e.g. `addAssumeNonNull()` in `PromoteMemoryToRegister.cpp`).

But we currently don't deal with such assumptions :)
The only way `isKnownNonZero()` handles assumptions is
by calling `computeKnownBits()` which calls `computeKnownBitsFromAssume()`.
But `x != 0` does not tell us anything about set bits,
it only says that there are *some* set bits.
So naturally, `KnownBits` does not get populated,
and we fail to make use of this assumption.

I propose to deal with this special case by special-casing it
via adding a `isKnownNonZeroFromAssume()` that returns boolean
when there is such an assumption.

Fixes PR43267 <https://bugs.llvm.org/show_bug.cgi?id=43267>.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D71660

Files:
  llvm/lib/Analysis/ValueTracking.cpp
  llvm/test/Transforms/InstCombine/assume.ll

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