https://bugs.llvm.org/show_bug.cgi?id=47238
Bug ID: 47238
Summary: [InstCombine] We need to recursively enqueue users of
instructions whose use-count changed
Product: libraries
Version: trunk
Hardware: PC
OS: Linux
Status: NEW
Severity: enhancement
Priority: P
Component: Scalar Optimizations
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected]
And i think we've finally found a fundamental issue :S
https://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20200817/821034.html
While so far we've managed to get out of all the extra iterations by
consistently
enqueueing all the operands to be revisited, i'm not sure it's really that
simple.
Here, we have basically the following:
%i0 = cmp with non-canonical pred
%i1 = not %i0
%i2 = some-op %i0
First time around, we don't manage to fold the %i1 (by flipping cmp predicate),
because %i0 has other uses, but manage to fold away %i2, reducing use count of
%i0.
We do enqueue %i0, but that does us no good, because we need to revisit %i1,
which we don't during this iteration.
So basically, not only do we need to enqueue the values whose use-count
changed,
we also need to recursively enqueue users of these instructions.
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