[PATCH] D125212: [GlobalISel] Allow destination patterns having empty outs

[Abinav Puthan Purayil via Phabricator via llvm-commits]

abinavpp added a comment.

In D125212#3500234 <https://reviews.llvm.org/D125212#3500234>, @arsenm wrote:

> I do think there should be a builtin hasOneUse pattern predicate the emitter could use to verify

If we have a `bit HasNoUse` builtin predicate in PatFrags we can get the matcher
table to check the empty usage of the result without the generic C++ predicates.
The problem I'm seeing here is that the default behaviour should be to not check
for the use count since most of the selection doesn't care about it. Having a
ternary HasNoUse builtin is fine since we could set it to false for selection
that needs at least 1 use (e.g.: AMDGPU's return atomic ops), true for selection
that needs no use (e.g.: AMDGPU's no return atomic ops), "don't care" for the
majority of the other selections. I don't think we can rely on the '?'
(uninitialized) value since TreePredicateFn::isPredefinedPredicateEqualTo()
return false for uninitialized fields.

How should we do this?


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