[PATCH] D70147: Repeat DevirtSCCRepeatedPass if new indirect calls are found.

[Hiroshi Yamauchi via Phabricator via llvm-commits]

yamauchi added a comment.

As I understand, that code around line 1323 of InlineCost.cpp would handle a simple case where a caller is passing a (constant) function pointer as a call argument and the callee simply calls it (constant propagation). But it wouldn't handle a (more complex) virtual call (vtable lookup though memory) on a stack allocated (in the caller) object passed to a callee, and would not work for this particular missed inlining case, at least, as is.

To handle such a case, it would have to add logic like the original patch (D69591 <https://reviews.llvm.org/D69591>) that detects a vtable look up pattern along with consideration for aliasing (since the vtable is in memory). But it'd be difficult to do because CallAnalyzer/InlineCost operates without actually having the code inlined (ie. interprocedural) and won't be able to reuse the facilities like llvm::FindAvailablePtrLoadStore.

It'd be conceivable to beef up CallAnalyzer to do this sort of things, but it'd be potentially non-trivial in complexity and compile-time-increasing.

The original patch D69591 <https://reviews.llvm.org/D69591> (which, I think is, fairly fine grained to this case, btw) doesn't have this issue because it applies right after the call is actually inlined and the scope of analysis becomes intraprocedural.


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