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Deduplicate unreachable blocks, for real this time by saethlin · Pull Request #1...
source link: https://github.com/rust-lang/rust/pull/110569
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In #106428 (in particular 41eda69) we noticed that inlining unreachable_unchecked can produce duplicate unreachable blocks. So we improved two MIR optimizations: SimplifyCfg was given a simplify to deduplicate unreachable blocks, then InstCombine was given a combiner to deduplicate switch targets that point at the same block. The problem is that change doesn't actually work.
Our current pass order is
SimplifyCfg (does nothing relevant to this situation)
Inline (produces multiple unreachable blocks)
InstCombine (doesn't do anything here, oops)
SimplifyCfg (produces the duplicate SwitchTargets that InstCombine is looking for)
So in here, I have factored out the specific function from InstCombine and placed it inside the simplify that produces the case it is looking for. This should ensure that it runs in the scenario it was designed for.
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