[PATCH] D93039: Introduce llvm.noalias.decl intrinsic

[Florian Hahn via Phabricator via llvm-commits]

fhahn added inline comments.


================
Comment at: llvm/lib/IR/Verifier.cpp:121
+    cl::desc("Ensure that llvm.experimental.noalias.scope.decl for identical "
+             "scopes are not dominating"));
+
----------------
jeroen.dobbelaere wrote:
> nikic wrote:
> > fhahn wrote:
> > > jeroen.dobbelaere wrote:
> > > > nikic wrote:
> > > > > Can we flip this flag now, or are you aware of any further issues?
> > > > I just did a test-suite run and a stage2 release build using an assertion build with the flag flipped, and both went fine. IMHO it makes sense to try it out...
> > > > 
> > > What's the impact on compile-time? If it is potentially expensive, it should probably be `true` for `EXPENSIVE_CHECKS` builds.
> > I see no reason for it to be expensive at least.
> @fhahn, @nikic, It's O(N log(N)) (sorting of N = number of scope declarations)
> Next to that, it is roughly k * O((M-1)^2) * O(dominance checking) with M the the number of identical scope declarations, and k the number if different scopes.
> In practice M should be pretty low (mostly 1) and O(N log(N)) should be the main part.
> 
> Is that considered to be too expensive ?
> 
> 
IIUC we need to potentially check whether any `llvm.experimental.noalias.scope.decl` dominates any other `llvm.experimental.noalias.scope.decl`? 


Is it possible to have a function with `N` basic blocks which do not dominate each other, each with `N` `llvm.experimental.noalias.scope.decl` for the same scope?


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D93039/new/

https://reviews.llvm.org/D93039