45198456be
Fixing the performance regression of #76244 Issue https://github.com/rust-lang/rust/issues/74865 suggested that removing the `def_id` field from `ParamEnv` would improve performance. PR https://github.com/rust-lang/rust/pull/76244 implemented this change. Generally, [results](https://perf.rust-lang.org/compare.html?start=80fc9b0ecb29050d45b17c64af004200afd3cfc2&end=5ef250dd2ad618ee339f165e9b711a1b4746887d) were as expected: an instruction count decrease of about a percent. The instruction count for the unicode crates increased by about 3%, which `@nnethercote` speculated to be caused by a quirk of inlining or codegen. As the results were generally positive, and for chalk integration, this was also a step in the right direction, the PR was r+'d regardless. However, [wall-time performance results](https://perf.rust-lang.org/compare.html?start=a055c5a1bd95e029e9b31891db63b6dc8258b472&end=7402a394471a6738a40fea7d4f1891666e5a80c5&stat=task-clock) show a much larger performance degradation: 25%, as [mentioned](https://github.com/rust-lang/rust/pull/76244#issuecomment-694459840) by `@Mark-Simulacrum.` This PR, for now, reverts #76244 and attempts to find out, which change caused the regression. |
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