[PATCH] D68492: [PATCH 09/38] [noalias] D9376: llvm.noalias - handling of dead intrinsics

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri added inline comments.


================
Comment at: llvm/lib/Analysis/InstructionSimplify.cpp:5156
+    if (isa<UndefValue>(Arg0) ||
+        (isa<ConstantPointerNull>(Arg0) &&
+         Arg0->getType()->getPointerAddressSpace() == 0))
----------------
jeroen.dobbelaere wrote:
> a.elovikov wrote:
> > What if we have
> > 
> >   %i = ptr2int %p
> >   %null = sub %i, %i
> >   %nullptr = int2ptr %null
> >   %scope = call @llvm.noalias(%nullptr) ; introduce the scope
> >   %null2 = ptr2int %scope
> >   %i2 = add %null2, %i
> >   %same.as.orig.p = int2ptr %i2
> > 
> > Why don't we want `%same.as.orig.p` to have the scope?
> A ptr2int will normally block the noalias propagation. Not sure if a 
>   %same.as.orig.p = getelementptr %scope, %i
> is valid when %scope is null. If that is valid, the noalias dependency should not be removed, and we should not short-circuit it here.
> 
`getelementptr` is valid for null pointer.



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