[PATCH] D76971: Deduce attributes for aligned_alloc in InstCombine

[Johannes Doerfert via Phabricator via llvm-commits]

jdoerfert added inline comments.


================
Comment at: llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp:4445
+                      Attribute::getWithDereferenceableOrNullBytes(
+                          Call.getContext(), Op1C->getZExtValue()));
   } else if (isReallocLikeFn(&Call, TLI) && Op1C) {
----------------
bondhugula wrote:
> jdoerfert wrote:
> > bondhugula wrote:
> > > jdoerfert wrote:
> > > > When Op0C is set (regardless of Op1C), we can set the alignment attribute on the return value, can't we?
> > > Would it be correct to set the alignment attribute for 0 sized allocations?
> > > Would it be correct to set the alignment attribute for 0 sized allocations?
> > 
> > Not in general, but: `The function aligned_alloc() is the same as memalign(), except for the added restriction that size should be a multiple of alignment.` So for a non-zero alignment size need to be non-zero. Please correct me if I'm wrong though.
> The size could still be zero. (zero as size would be a multiple of any alignment. :-))
> The size could still be zero. (zero as size would be a multiple of any alignment. :-))

True, it was late.

Then remove the "(regardless of Op1C),") from my original comment. We still can and should add alignment information. 


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Comment at: llvm/test/Transforms/InstCombine/deref-alloc-fns.ll:39
+  ret i8* %call
+}
+
----------------
I mean, we can add `align 32` here can't we not?


Repository:
  rG LLVM Github Monorepo

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  https://reviews.llvm.org/D76971/new/

https://reviews.llvm.org/D76971