[PATCH] D150179: [GlobalISel] Hide hoisted constants behind G_BITCAST to prevent folding.

[Amara Emerson via Phabricator via llvm-commits]

aemerson added a comment.

In D150179#4328938 <https://reviews.llvm.org/D150179#4328938>, @arsenm wrote:

> Seems like this is another one of those DAG workaround passes we ideally wouldn't need to keep running

I thought so too, but reading its documentation more I think the problem it's solving is actually agnostic to selectors. That is, the core issue isn't that DAG can only see basic blocks, but one of balancing CSE & register pressure. We could stop running this IR pass (which does exist as IR due to SDAG's nature), but we'd just need to implement something similar in the GISel pipeline anyway.



================
Comment at: llvm/test/CodeGen/AArch64/GlobalISel/irtranslator-hoisted-constants.ll:29
+entry:
+  %hc = bitcast i32 100000 to i32
+  br label %cont
----------------
arsenm wrote:
> Also add some vector cases?
Good point, constant hoisting doesn't touch vector constants so we can avoid this bitcast trickery for those.


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