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[AARCH64] Improve accumulator forwarding for Cortex-A57 model

Authored by mnadeem on Jan 4 2021, 2:58 AM.

Description

[AARCH64] Improve accumulator forwarding for Cortex-A57 model

The old CPU model only had MLA->MLA forwarding. I added some missing
MUL->MLA read advances and a missing absolute diff accumulator read
advance according to the Cortex A57 Software Optimization Guide.

The patch improves performance in EEMBC rgbyiqv2 by about 6%-7% and
spec2006/milc by 8% (repeated runs on multiple devices), causes no
significant regressions (none in SPEC).

Differential Revision: https://reviews.llvm.org/D92296

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