[llvm] [SystemZ] SLP reductions: cost functions of reductions and scalarization (PR #112491)

[Alexey Bataev via llvm-commits]

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+; RUN: opt -S --passes=slp-vectorizer -mtriple=s390x-unknown-linux -mcpu=z16 < %s | FileCheck %s
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alexey-bataev wrote:

1. The test itself better to precommit in a separate NFC patch anyway.
2. There should be the difference, otherwise it is meaningless. No need to check other passes, SLP vectorizer has its own cost estimation, which can be obtained via `-pass-remarks-output=` options. There are several tests already, which use it.

https://github.com/llvm/llvm-project/pull/112491