[BasicAA] Improve escape source analysis for return-only captures #131869
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This fixes an issue where improving inference from a general capture to a return-only capture can make alias analysis results worse. The problem is that if there are return-only captures, the call can no longer treated as a plain escape source, as the call result may alias one of the return-only-capture arguments, even if they don't escape. Fix this by having isEscapeSource() return the relevant arguments and explicitly check that these aren't aliased. Fixes llvm#131168.
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This approach has too much compile-time impact: https://llvm-compile-time-tracker.com/compare.php?from=761c4d73eb648ba24895da9580c398f9799a3dfc&to=7b295d82d2828f2b018240c59db7bbdf4f78a832&stat=instructions:u |
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There are some improvements on llvm-opt-benchmark, but not a lot. Would be nice to fix this somehow, but it's not particularly important and not worth increasing compile-time for. |
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This fixes an issue where improving inference from a general capture to a return-only capture can make alias analysis results worse.
The problem is that if there are return-only captures, the call can no longer treated as a plain escape source, as the call result may alias one of the return-only-capture arguments, even if they don't escape.
Fix this by having isEscapeSource() return the relevant arguments and explicitly check that these aren't aliased.
Fixes #131168.