[PATCH] D64258: [InferFuncAttributes] extend 'dereferenceable' attribute based on loads

[Sanjay Patel via Phabricator via llvm-commits]

spatel added a comment.

In D64258#1578820 <https://reviews.llvm.org/D64258#1578820>, @jfb wrote:

> Right now the control flow isn't clever, but I wonder if, as this analysis becomes more powerful, it'll have to act differently when `-fno-delete-null-pointer-checks` is specified? Is there a simple test that you can add to make sure null pointer checks don't cause false assumptions whenever this optimization becomes smarter?


I hadn't seen that flag before. In IR we have this translation of the minimal test in clang/test/CodeGen/nonnull.c:

  define void @foo(i32* nocapture dereferenceable(4) %x) #0 {
    store i32 0, i32* %x, align 4, !tbaa !3
    ret void
  }
  
  attributes #0 = { ... "null-pointer-is-valid"="true" ... }

This pass/patch doesn't act on the dereferenceable attribute; it just adds it. So some other pass would be at risk if it tries a transform based on "dereferenceable" without checking the "null-pointer-is-valid" function attribute or "nonnull" argument attribute? Argument::hasNonNullAttr() seems safe.


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