0f82469314
IndVars may be able to replace a loop dependent condition with a loop invariant one, but loop-unswitch runs before IndVars, so the invariant check remains in the loop. For an example, consider a read-only loop with a bounds check: https://godbolt.org/z/8cdj4qhbG This patch uses a approach similar to the way extra cleanup passes are run on demand after vectorization (added in acea6e9cfa4c4a0e8678c7). It introduces a new ShouldRunExtraSimpleLoopUnswitch analysis marker, which IndVars can use to indicate that extra unswitching is beneficial. ExtraSimpleLoopUnswitchPassManager uses this analysis to determine whether to run its passes on a loop. Compile-time impact (geomean) ranges from +0.0% to 0.02% https://llvm-compile-time-tracker.com/compare.php?from=138c0beb109ffe47f75a0fe8c4dc2cdabe8a6532&to=19e6e99eeb280d426907ea73a21b139ba7225627&stat=instructions%3Au Compile-time impact (geomean) of unconditionally running SimpleLoopUnswitch ranges from +0.05% - +0.16% https://llvm-compile-time-tracker.com/compare.php?from=138c0beb109ffe47f75a0fe8c4dc2cdabe8a6532&to=2930dfd5accdce2e6f8d5146ae4d626add2065a2&stat=instructions:u Unconditionally running SimpleLoopUnswitch seems to indicate that there are multiple other scenarios where we fail to run unswitching when opportunities remain. Fixes https://github.com/llvm/llvm-project/issues/85551. PR: https://github.com/llvm/llvm-project/pull/81271