Fix issues with EH in unexecuted loops #82329
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Tagging subscribers to this area: @JulieLeeMSFT, @jakobbotsch, @kunalspathak Issue DetailsFix two problems with code in loops that are determined to not execute that have exception handling clauses:
Fixes #81675
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Fix two problems with code in loops that are determined to not execute that have exception handling clauses: 1. Be more specific in loop unrolling to avoid unrolling even zero-count loops (which causes the loop to be removed) if there is a block in the loop with a different handler region than the handler region of the "top" block. This should only kick in for x86, where handlers are not extracted as funclets. 2. In Value Numbering, before actually value numbering nodes, `optComputeLoopSideEffectsOfBlock()` walks all the blocks of all top-level loops collecting data. Unfortunately, it sets the Value Number of certain nodes as a way to pass information "up the tree" during processing. Presumably these "fake" value numbers actually get replaced during actual value numbering for the tree. However, when we go to actually value number the IR, we only walk reachable blocks. Thus, in some cases, we would end up with a top-level "fake" value number on an unreachable statement root, thus leading `fgDebugCheckExceptionSets()` to check the tree and assert. To fix this, at the end of the `optComputeLoopSideEffectsOfBlock()`, clear the VN in case it was previously set. Fixes dotnet#81675
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@AndyAyersMS @jakobbotsch PTAL |
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Feb 22, 2023
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Fix two problems with code in loops that are determined to not execute that have exception handling clauses:
optComputeLoopSideEffectsOfBlock()walks all the blocks of all top-level loops collecting data. Unfortunately, it sets the Value Number of certain nodes as a way to pass information "up the tree" during processing. Presumably these "fake" value numbers actually get replaced during actual value numbering for the tree. However, when we go to actually value number the IR, we only walk reachable blocks. Thus, in some cases, we would end up with a top-level "fake" value number on an unreachable statement root, thus leadingfgDebugCheckExceptionSets()to check the tree and assert. To fix this, at the end of theoptComputeLoopSideEffectsOfBlock(), clear the VN in case it was previously set.Fixes #81675