[PATCH] D69227: [LICM] Support hosting of dynamic allocas out of loops

[Artur Pilipenko via Phabricator via llvm-commits]

apilipenko accepted this revision.
apilipenko added inline comments.
This revision is now accepted and ready to land.


================
Comment at: lib/Transforms/Scalar/LICM.cpp:796-799
+  // TODO: This looks a lot like capture tracking, but we need to remove any
+  // invariant starts if we extend the lifetime of the alloca by hoisting it.
+  // We should probably refactor capture tracking into a form which allows us
+  // to reuse the relevant bits and remove the duplicated logic here.
----------------
This is even more restrictive. We can't let alloca be used in a phi, so this value can be observed in a different iteration. 
```
for.body:
  %iv = phi i64 [ %iv.next, %for.body ], [ 0, %entry ]
  %p = phi i64* [ %a, %for.body ], [ %x, %entry ]
  %a = alloca i64
  ; In the orginal program %p and %a point to different locations and don't alias
  ; If you hoist the alloca %p %a will point to the same memory location
  %iv.next = add nuw nsw i64 %iv, 1
  %exitcond = icmp ult i64 %iv, %n
  br i1 %exitcond, label %for.body, label %exit
```
It would be nice to have a test like this.


Repository:
  rL LLVM

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D69227/new/

https://reviews.llvm.org/D69227