[PATCH] D53137: Scalable vector core instruction support + size queries

[Graham Hunter via Phabricator via llvm-commits]

huntergr added inline comments.


================
Comment at: llvm/include/llvm/IR/DataLayout.h:454
+    auto BaseSize = getTypeSizeInBits(Ty);
+    return { (BaseSize.getKnownMinSize() + 7) / 8, BaseSize.isScalable() };
   }
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rovka wrote:
> We already overload operator /, why not overload + as well so we don't have to change the body of this method?
Scaling a size with * or / has a clear meaning to me, since it's independent of vscale; getting a vector that's half the size or four times larger just works.

Using + (or -) on the other hand doesn't seem to be as clear; I wasn't sure if a standalone int should be automatically treated as being the same as the TypeSize, or always considered Fixed. If we try for the former I can imagine quite a few bugs arising.

I could add a roundBitsToNearestByteSize method to move the arithmetic elsewhere if that would be acceptable?


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Comment at: llvm/include/llvm/IR/DataLayout.h:656
+                     getTypeSizeInBits(VTy->getElementType()).getKnownMinSize();
+    return ScalableSize(MinBits, EltCnt.Scalable);
   }
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rovka wrote:
> Maybe just return VTy->getElementCount() * getTypeSizeInBits(VTy->getElementType()).getFixedSize().
There's no support for generating a TypeSize from an ElementCount in that way; is that an interface you feel is useful?

(I'll certainly change the `getKnownMinSize` to `getFixedSize` though, since we're just referring to a scalar)


Repository:
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  https://reviews.llvm.org/D53137/new/

https://reviews.llvm.org/D53137