iree: [CPU][ARM] DT+UK 50x slower than Default flags on BF16 on Android

What happened?

name	threads	Default flags latency (ms)	DT+UK latency (ms)
BERT_BASE_BF16_JAX_I32_SEQLEN8	1	69.1	3963.0
BERT_BASE_BF16_JAX_I32_SEQLEN32	1	172.0	15964.0
BERT_BASE_BF16_JAX_I32_SEQLEN64	1	326.0	32015.0

Steps to reproduce your issue

1. Download MLIR: https://storage.googleapis.com/iree-model-artifacts/jax/jax_models_0.4.19_1698302455/BERT_BASE_BF16_JAX_I32_SEQLEN8/stablehlo.mlirbc

2. Compile:

ARM_CPU_FEATURES="+v9a,+fullfp16,fp-armv8,+neon,+aes,+sha2,+crc,+lse,+rdm,+complxnum,+rcpc,+sha3,+sm4,+dotprod,+fp16fml,+dit,+flagm,+ssbs,+sb,+altnzcv,+fptoint,+bf16,+i8mm,+bti"

iree-compile stablehlo.mlirbc \
    --iree-hal-target-backends="llvm-cpu" \
    --iree-input-type="stablehlo" \
    --iree-llvmcpu-link-embedded=false \
    --iree-input-demote-f64-to-f32=false \
    --iree-input-demote-i64-to-i32=false \
    --iree-llvmcpu-target-cpu-features="${ARM_CPU_FEATURES}" \
    --iree-llvmcpu-target-triple="aarch64-none-linux-android34" \
    # For DT+UK.
    --iree-opt-data-tiling \
    --iree-llvmcpu-enable-microkernels \
    -o module.vmfb

1. Run on device

iree-benchmark-module --module=module.vmfb --task_topology_cpu_ids=0 --device=local-task --function=main --input=1x8xi32=0 --input=1x8xi32=0

What component(s) does this issue relate to?

Compiler

Version information

675aafb

Additional context

No response