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combines) until they are legal. Doing it the old way could, when the stars align *just* right, cause a node to get into the combine set prior to being legalized. Then, when the same node showed up as an operand to another node later on (but not so much later on that it had been deleted as dead) we would fail to add it back to the worklist thinking it had already been combined. This would in turn cause it to not be legalized. Fortunately, we can also walk the operands looking for uncombined (and thus potentially un-legalized) nodes late. It will still ensure that we walk all operands of all nodes and send all of them through both the legalizer without changes and the combiner at least once. (Which was the original goal of this). I have a test case for this bug, but it is terribly brittle. For example, it will stop finding the bug the moment I enable the new shuffle lowering. I don't yet have any test case that reliably exercises this bug, and it isn't clear that it will be possible to craft one. It is entirely possible that with the new shuffle lowering the two forms of doing this are precisely equivalent. That doesn't mean we shouldn't take the more conservative approach of insisting on things in the combined set having survived the legalizer. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@214673 91177308-0d34-0410-b5e6-96231b3b80d8
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