[PATCH] D74651: Add IR constructs for inalloca replacement preallocated call setup

[Eli Friedman via Phabricator via llvm-commits]

efriedma added a comment.

> I think if we model calls with preallocated bundles as modifying inaccessible state (i.e. the stack pointer), LLVM transforms won't do this.

I don't think that's enough in general.  Well, maybe it's enough for the transforms we actually implement... LLVM currently has very few transforms that fold code together.

But a simple example, suppose we had a transform that took `void g(); void f() { g();g();g();g();g(); }` and transformed it into something like `void g(); void f() { for (int i =0; i < n; ++i) g(); }`.  Looks fine generally.  If the loop body is a sequence containing calls to `llvm.call.preallocated.setup()`/`llvm.call.preallocated.arg()`, maybe not so fine.  (I think this is only an issue if there is no call actually consuming the stack; if there were, the token would block the transform.)


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  https://reviews.llvm.org/D74651/new/

https://reviews.llvm.org/D74651