[llvm] [LV] Linear argument tests for vectorization of function calls (PR #73936)

[Maciej Gabka via llvm-commits]

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+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 2
+; RUN: opt < %s -passes=loop-vectorize,instsimplify -force-vector-interleave=1 -S | FileCheck %s
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mgabka wrote:

I also think we should add at least one test case where step is negative, as that is allowed I think. 
The VFABI mangling allows it, from the specification: "For example, linear(val(i):-3) gives Ln3 when the type of i is integer"

https://github.com/llvm/llvm-project/pull/73936