PR for llvm/llvm-project#66868 #705
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The in-loop successor is only on the left after a potential condition inversion. As we re-use the old condition as-is, we should also reuse the old successors as-is. Fixes llvm/llvm-project#63962. (cherry picked from commit afd7db48c55cb87566758e961f1ebac8af16b8bc)
When unswitching via invariant condition injection, we currently mark the condition in the old loop, so that it does not get unswitched again. However, if there are multiple branches for which conditions can be injected, then we can do that for both the old and new loop. This means that the number of unswitches increases exponentially. Change the handling to be more similar to partial unswitching, where we instead mark the whole loop, rather than a single condition. This means that we will only generate a linear number of loops. TBH I think even that is still highly undesirable, and we should probably be unswitching all candidates at the same time, so that we end up with only two loops. But at least this mitigates the worst case. The test case is a reduced variant that generates 1700 lines of IR without this patch and 290 with it. Fixes llvm/llvm-project#66868. (cherry picked from commit 8362cae71b80bc43c8c680cdfb13c495705a622f)
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@nikic good to merge into 17.0.1? |
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Yeah, this fixes some compiler hangs we've encountered in the wild. |
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resolves llvm/llvm-project#66868