Jeremy Morse 19b65a9c02 [DebugInfo][RemoveDIs] Add a DPValue implementation for instcombine sinking (#77930) ...

In instcombine, when we sink an instruction into a successor block, we try
to clone and salvage all the variable assignments that use that Value. This
is a behaviour that's (IMO) flawed, but there are important use cases where
we want to avoid regressions, thus we're implementing this for the
non-instruction debug-info representation.

This patch refactors the dbg.value sinking code into it's own function, and
installs a parallel implementation for DPValues, the non-instruction
debug-info container. This is mostly identical to the dbg.value
implementation, except that we don't have an easy-to-access ordering
between DPValues, and have to jump through extra hoops to establish one in
the (rare) cases where that ordering is required.

The test added represents a common use-case in LLVM where these behaviours
are important: a loop has been completely optimised away, leaving several
dbg.values in a row referring to an instruction that's going to sink. The
dbg.values should sink in both dbg.value and RemoveDIs mode, and
additionally only the last assignment should sink.

2024-01-25 23:28:56 +00:00

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