[llvm] [WIP][LoopIdiomVectorize] Recognize and transform minidx pattern (PR #144987)

[David Sherwood via llvm-commits]

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+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -passes=loop-vectorize -force-vector-width=1 -force-vector-interleave=4 -S %s | FileCheck %s --check-prefix=CHECK-REV-MIN-VW1-IL4
+; RUN: opt -passes=loop-vectorize -force-vector-width=4 -force-vector-interleave=1 -S %s | FileCheck %s --check-prefix=CHECK-REV-MIN-VW4-IL1
+; RUN: opt -passes=loop-vectorize -force-vector-width=4 -force-vector-interleave=2 -S %s | FileCheck %s --check-prefix=CHECK-REV-MIN-VW4-IL2
+; RUN: opt -passes=loop-idiom-vectorize -S -mtriple=aarch64 -mattr=+sve %s | FileCheck %s --check-prefix=CHECK-LOOP-IDIOM
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david-arm wrote:

I think before landing the tests it's probably worth thinking about which pass/transform you actually want to use for your end goal. If your goal is to support general loop vectorisation then the tests should live in LoopVectorize and development should take place in LoopVectorizer/VPlan. The main intention of this pass is to support vectorisation of some common idioms that are unlikely to be supported in the loop vectoriser in the short-medium term. However, the ideal is still to migrate over to the loop vectoriser once that support exists.

https://github.com/llvm/llvm-project/pull/144987