Up to 8% RSS regression because of #44142

[arielb1]

http://perf.rust-lang.org/?start=2017-08-15T00%3A00%3A00%2B00%3A00&end=2017-09-14T00%3A00%3A00%2B00%3A00&crates=%5B%22futures-rs-test-all%22%2C%22helloworld%22%2C%22html5ever-2016-08-25%22%2C%22hyper.0.5.0%22%2C%22inflate-0.1.0%22%2C%22issue-20936-deep-vector%22%2C%22issue-32062-equality-relations-complexity%22%2C%22issue-32278-big-array-of-strings%22%2C%22issue-43572-unused-uses%22%2C%22jld-day15-parser%22%2C%22piston-image-0.10.3%22%2C%22regex-0.1.80%40010-baseline%22%2C%22regex-0.1.80%40020-incr-from-scratch%22%2C%22regex-0.1.80%40030-compile_one%22%2C%22regex-0.1.80%40040-is_valid_cap_letter%22%2C%22regex-0.1.80%40050-expand%22%2C%22regex-0.1.80%40060-Compiler-new%22%2C%22regex-0.1.80%40070-BYTE_FREQUENCIES%22%2C%22regex-0.1.80%40080-SparseSet%22%2C%22regex-0.1.80%40090-Job%22%2C%22regex-0.1.80%40100-incr-no-change%22%2C%22regex.0.1.30%22%2C%22rust-encoding-0.3.0%22%2C%22syntex-0.42.2%40000-base%22%2C%22syntex-0.42.2%40010-incr%22%2C%22syntex-0.42.2%40020-clean%22%2C%22tokio-webpush-simple%40000-base%22%2C%22tokio-webpush-simple%40010-incr%22%2C%22tokio-webpush-simple%40020-clean%22%2C%22tokio-webpush-simple%40030-minor-change%22%2C%22tuple-stress%22%5D&stat=max-rss

This is an 8% regression with incremental enabled, 1% without it. #44142

[alexcrichton]

A more focused graph

[alexcrichton]

Interestingly if you widen the view a bit you'll see:

• An 8% regression due to Migrate a slew of metadata methods to queries #44142
• A 4% improvement due to Use NodeId/HirId instead of DefId for local variables. #44316
• A 7% improvement due to rustc: Remove HirId from queries #44435
• A 7% regression due to Evaluate fixed-length array length expressions lazily. #44275

May be worth looking into #44275 as well?

[alexcrichton]

Specifically before/after #44142, massif snapshots -- I've only included the peak snapshot in the output there.

[alexcrichton]

Looks like basically all of the memory is here, aka we have a bigger dep graph. Turns out adding more queries makes a bigger dep graph :)

[alexcrichton]

I cashed in some easy savings in #44586, but it doesn't actually fix the "regression", but we likely shouldn't call it a regression as it also fixed a number of would-be bugs!