[llvm] [LV] Convert gather loads with invariant stride into strided loads (PR #147297)

[Florian Hahn via llvm-commits]

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@@ -3307,6 +3332,52 @@ struct VPWidenLoadEVLRecipe final : public VPWidenMemoryRecipe, public VPValue {
   }
 };
 
+/// A recipe for strided load operations, using the base address, stride, and an
+/// optional mask. This recipe will generate an vp.strided.load intrinsic call
+/// to represent memory accesses with a fixed stride.
+struct VPWidenStridedLoadRecipe final : public VPWidenMemoryRecipe,
+                                        public VPValue {
+  VPWidenStridedLoadRecipe(LoadInst &Load, VPValue *Addr, VPValue *Stride,
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fhahn wrote:

> First, the current VPWidenIntrinsicRecipe cannot set attributes, so alignment information will be lost. This could be resolved by passing an AttributeList to VPWidenIntrinsicRecipe, allowing it to add the attributes during ::execute.

Hm yes, this is a general modeling issue, but could be improved separately (and does not only apply to this intrinsic I think). Is setting the alignment critical for the initial implementation?

> Next, it might become difficult to ensure profitability before generating the strided access (i.e., we may not be able to achieve the change suggested in this comment

I am not sure I understand this completely; We should be able to check the profitability up-front regardless of what recipe we create later on, I think?

> Finally, using VPWidenIntrinsicRecipe reduces readability during transformations. Currently, VPWidenStridedLoadRecipe provides members like getAddr() and getStride(), which improves readability. This issue is not limited to EVL lowering—it should also have an impact #164205.

I think this could be mostly taken care of by providing a `m_StridedLoad()` pattern?

https://github.com/llvm/llvm-project/pull/147297