[compile] Fix inductor partition config

[angelayi]

When trying to run the following cmd, I ran into this assertion error because self.backend is equal to "".

vllm bench latency \
    --model=RedHatAI/Meta-Llama-3.1-8B-Instruct-FP8 \
    --output-len 1 --input-len 8192 --batch-size 1 \
    --tensor-parallel-size 8 --load-format dummy \
    --num_iters_warmup 5 --num_iters 15 \
    -O '{"level": 3, "pass_config": {"enable_async_tp": true, "enable_sequence_parallelism": true}, "use_inductor_graph_partition": true, "custom_ops":["+quant_fp8"], "cudagraph_mode":"FULL_AND_PIECEWISE"}' \
    --no-enable-prefix-caching

cc @ProExpertProg @zou3519 @BoyuanFeng @baonudesifeizhai

[gemini-code-assist]

Code Review

This pull request correctly fixes a bug in the inductor partition configuration. The is_attention_compiled_piecewise method was previously checking self.backend == "inductor", which would incorrectly evaluate to false when the default backend (an empty string) is used with inductor. The change to check self.use_inductor is the correct approach, as this flag accurately indicates whether inductor compilation is enabled. This resolves the assertion error described in the pull request.

[ProExpertProg]

Yep, bad merge of #25845 after #26113 was reverted in #26472. @morrison-turnansky can you fix in #26502?

[morrison-turnansky]

@ProExpertProg yes, will do