[llvm] [MachineCombiner][NFC]Add tests for long chain FMA reassociation, NFC (PR #224126)

[Craig Topper via llvm-commits]

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@@ -0,0 +1,348 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 6
+; RUN: llc -O3 -mtriple=aarch64 -mcpu=neoverse-v2 < %s | FileCheck %s
+
+; A long chain of FMA accumulations is reassociated into two shorter chains
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topperc wrote:

Where is the main patch? Nothing in this PR links to it.

https://github.com/llvm/llvm-project/pull/224126