[clang] [llvm] [AArch64][SelectionDAG] Add CodeGen support for scalar FEAT_CPA (PR #105669)

[Rodolfo Wottrich via llvm-commits]

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+; RUN: llc -mtriple=aarch64 -verify-machineinstrs --mattr=+cpa -O0 -global-isel=0 -fast-isel=0 %s -o - 2>&1 | FileCheck %s --check-prefixes=CHECK-CPA-O0
+; RUN: llc -mtriple=aarch64 -verify-machineinstrs --mattr=+cpa -O3 -global-isel=0 -fast-isel=0 %s -o - 2>&1 | FileCheck %s --check-prefixes=CHECK-CPA-O3
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rgwott wrote:

It is interesting to have because sometimes the instruction selected is different, allowing us to exercise both. This did however get a little bit less useful with the removal of a SelectionDAG fold opportunity during the course of this PR. But I am in favour of keeping it.

https://github.com/llvm/llvm-project/pull/105669