[llvm] [ARM]Adjust cost of muls in SMLAL patterns (PR #122713)

[Nashe Mncube via llvm-commits]

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+; RUN: opt -passes="print<cost-model>" 2>&1 -disable-output -mtriple thumbv8.1-m.main -mattr=+mve,+dsp  < %s | FileCheck %s
+define i64 @test(i16 %a, i16 %b) {
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nasherm wrote:

Done

https://github.com/llvm/llvm-project/pull/122713