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Preserve nonnull metadata on Loads through SROA & mem2reg #90
Commits on Jul 1, 2017
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Preserve nonnull metadata on Loads through SROA & mem2reg.
Summary: https://llvm.org/bugs/show_bug.cgi?id=31142 : SROA was dropping the nonnull metadata on loads from allocas that got optimized out. This patch simply preserves nonnull metadata on loads through SROA and mem2reg. Reviewers: chandlerc, efriedma Reviewed By: efriedma Subscribers: hfinkel, spatel, efriedma, arielb1, davide, llvm-commits Differential Revision: https://reviews.llvm.org/D27114 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@298540 91177308-0d34-0410-b5e6-96231b3b80d8
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[InstCombine] Factor the logic for propagating !nonnull and !range
metadata out of InstCombine and into helpers. NFC, this just exposes the logic used by InstCombine when propagating metadata from one load instruction to another. The plan is to use this in SROA to address PR32902. If anyone has better ideas about how to factor this or name variables, I'm all ears, but this seemed like a pretty good start and lets us make progress on the PR. This is based on a patch by Ariel Ben-Yehuda (D34285). git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@306267 91177308-0d34-0410-b5e6-96231b3b80d8
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[SROA] Clean up a test case a bit prior to adding more testing for
nonnull as part of fixing PR32902. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@306353 91177308-0d34-0410-b5e6-96231b3b80d8
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[SROA] Further test cleanup and add a test for the actual propagation of
the nonnull attribute distinct from rewriting it into an assume. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@306358 91177308-0d34-0410-b5e6-96231b3b80d8
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[SROA] Fix PR32902 by more carefully propagating !nonnull metadata.
This is based heavily on the work done ni D34285. I mostly wanted to do test cleanup for the author to save them some time, but I had a really hard time understanding why it was so hard to write better test cases for these issues. The problem is that because SROA does a second rewrite of the loads and because we *don't* propagate !nonnull for non-pointer loads, we first introduced invalid !nonnull metadata and then stripped it back off just in time to avoid most ways of this PR manifesting. Moving to the more careful utility only fixes this by changing the predicate to look at the new load's type rather than the target type. However, that *does* fix the bug, and the utility is much nicer including adding range metadata to model the nonnull property after a conversion to an integer. However, we have bigger problems because we don't actually propagate *range* metadata, and the utility to do this extracted from instcombine isn't really in good shape to do this currently. It *only* handles the case of copying range metadata from an integer load to a pointer load. It doesn't even handle the trivial cases of propagating from one integer load to another when they are the same width! This utility will need to be beefed up prior to using in this location to get the metadata to fully survive. And even then, we need to go and teach things to turn the range metadata into an assume the way we do with nonnull so that when we *promote* an integer we don't lose the information. All of this will require a new test case that looks kind-of like `preserve-nonnull.ll` does here but focuses on range metadata. It will also likely require more testing because it needs to correctly handle changes to the integer width, especially as SROA actively tries to change the integer width! Last but not least, I'm a little worried about hooking the range metadata up here because the instcombine logic for converting from a range metadata *to* a nonnull metadata node seems broken in the face of non-zero address spaces where null is not mapped to the integer `0`. So that probably needs to get fixed with test cases both in SROA and in instcombine to cover it. But this *does* extract the core PR fix from D34285 of preventing the !nonnull metadata from being propagated in a broken state just long enough to feed into promotion and crash value tracking. On D34285 there is some discussion of zero-extend handling because it isn't necessary. First, the new load size covers all of the non-undef (ie, possibly initialized) bits. This may even extend past the original alloca if loading those bits could produce valid data. The only way its valid for us to zero-extend an integer load in SROA is if the original code had a zero extend or those bits were undef. And we get to assume things like undef *never* satifies nonnull, so non undef bits can participate here. No need to special case the zero-extend handling, it just falls out correctly. The original credit goes to Ariel Ben-Yehuda! I'm mostly landing this to save a few rounds of trivial edits fixing style issues and test case formulation. Differental Revision: D34285 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@306379 91177308-0d34-0410-b5e6-96231b3b80d8
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