[PATCH] D31711: [GlobalISel] LegalizerInfo: Check if the vector element type is power of 2

[Kristof Beyls via Phabricator via llvm-commits]

kristof.beyls added inline comments.


================
Comment at: lib/CodeGen/GlobalISel/LegalizerInfo.cpp:78-81
+  LLT Ty = Aspect.Type;
+  unsigned SizeInBits =
+      Ty.isVector() ? Ty.getElementType().getSizeInBits() : Ty.getSizeInBits();
+  if (!isPowerOf2_64(SizeInBits))
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I was confused by the summary on this patch - I thought you wanted to make sure vector types like <3 x s32> definitely wouldn't be legalized and thought the existing code could sometimes legalize them. It then started doing the following train-of-thought:
"""
For vector types, getSizeInBits() returns the "number of elements" times "element size in bits".
That result can only be a power of 2 if both "number of elements" and "element size in bits" are both a power of 2.
So, the effect of this change would be to allow more vector data types, like <3 x s32> to be legalized."

So, in summary, by the time this gets committed, I think the commit message must be clearer, and e.g. state "Enable legalization of vector types with non-power-of-2 number of elements".

This patch clearly is missing tests.



https://reviews.llvm.org/D31711