JIT: work around issue with GDV and Boxing #56126
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If a call is a GDV candidate and returns a struct via hidden buffer, and that return value is immediately boxed, the GDV expansion will produce IR in incorrect order, leading to bad codegen. This seems to be a rare enough sequence that disabling GDV is a reasonable workaround for now. Actually the box expansion is producing IR in the wrong order and GDV fails to fix the order (unlike inlining, which does fix the order). Longer term we should avoid producing out of order IR. But that seems a bit more complicated and may have other CQ impact. Added a test case. Closes dotnet#53549.
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@EgorBo PTAL Not thrilled with dropping GDV for some call sites, but doing this avoids the problem, and the number of cases where we see this pattern is likely pretty small. No diffs in SPMI (other fix attempts had ~100's of diffs in asp.net). Also I'm able to run libraries xunit test harness under tiered PGO without odd errors. |
EgorBo
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Jul 22, 2021
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If a call is a GDV candidate and returns a struct via hidden buffer, and that
return value is immediately boxed, the GDV expansion will produce IR in
incorrect order, leading to bad codegen.
This seems to be a rare enough sequence that disabling GDV is a reasonable
workaround for now.
Actually the box expansion is producing IR in the wrong order and GDV fails
to fix the order (unlike inlining, which does fix the order).
Longer term we should avoid producing out of order IR. But that seems a bit
more complicated and may have other CQ impact.
Added a test case.
Closes #53549.