[PATCH] D24031: [InstCombine] replace fold of an icmp pattern that should never happen with an assert
Sanjay Patel via llvm-commits
llvm-commits at lists.llvm.org
Wed Aug 31 11:35:03 PDT 2016
spatel added a comment.
In https://reviews.llvm.org/D24031#530611, @efriedma wrote:
> Are you absolutely sure we can't trigger the assertion? I don't think there's any guarantee instcombine will visit the "and" before the "icmp".
Hmm...that would kill my (possibly wrong) mental model of InstCombine as a top-down / greedy machine. Is the comment in AddReachableCodeToWorklist() enough?
// Once we've found all of the instructions to add to instcombine's worklist,
// add them in reverse order. This way instcombine will visit from the top
// of the function down.
If that's not a valid assumption or if there's some other way that the worklist order doesn't match the instruction order, then I agree we can't assert here.
In that case, I think it should still be valid to remove the block of code (but don't add the assert). The regression test verifies that we get the end result that we want.
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