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Summary: After a discussion with Rekka, i believe this (or a small variant) should fix the remaining phi-of-ops problems. Rekka's algorithm for completeness relies on looking up expressions that should have no leader, and expecting it to fail (IE looking up expressions that can't exist in a predecessor, and expecting it to find nothing). Unfortunately, sometimes these expressions can be simplified to constants, but we need the lookup to fail anyway. Additionally, our simplifier outsmarts this by taking these "not quite right" expressions, and simplifying them into other expressions or walking through phis, etc. In the past, we've sometimes been able to find leaders for these expressions, incorrectly. This change causes us to not to try to phi of ops such expressions. We determine safety by seeing if they depend on a phi node in our block. This is not perfect, we can do a bit better, but this should be a "correctness start" that we can then improve. It also requires a bunch of caching that i'll eventually like to eliminate. The right solution, longer term, to the simplifier issues, is to make the query interface for the instruction simplifier/constant folder have the flags we need, so that we can keep most things going, but turn off the possibly-invalid parts (threading through phis, etc). This is an issue in another wrong code bug as well. Reviewers: davide, mcrosier Subscribers: sanjoy, llvm-commits Differential Revision: https://reviews.llvm.org/D37175 llvm-svn: 312401
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