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We sometimes see code like this: Case 1: %gep = getelementptr i32, i32* %a, <2 x i64> %splat %ext = extractelement <2 x i32*> %gep, i32 0 or this: Case 2: %gep = getelementptr i32, <4 x i32*> %a, i64 1 %ext = extractelement <4 x i32*> %gep, i32 0 where there is only one use of the GEP. In such cases it makes sense to fold the two together such that we create a scalar GEP: Case 1: %ext = extractelement <2 x i64> %splat, i32 0 %gep = getelementptr i32, i32* %a, i64 %ext Case 2: %ext = extractelement <2 x i32*> %a, i32 0 %gep = getelementptr i32, i32* %ext, i64 1 This may create further folding opportunities as a result, i.e. the extract of a splat vector can be completely eliminated. Also, even for the general case where the vector operand is not a splat it seems beneficial to create a scalar GEP and extract the scalar element from the operand. Therefore, in this patch I've assumed that a scalar GEP is always preferrable to a vector GEP and have added code to unconditionally fold the extract + GEP. I haven't added folds for the case when we have both a vector of pointers and a vector of indices, since this would require generating an additional extractelement operation. Tests have been added here: Transforms/InstCombine/gep-vector-indices.ll Differential Revision: https://reviews.llvm.org/D101900 |
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