Fixing the performance regression of #76244#76913
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bors merged 1 commit intorust-lang:masterfrom Sep 22, 2020
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Issue #74865 suggested that removing the
def_idfield fromParamEnvwould improve performance. PR #76244 implemented this change.Generally, results 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 show a much larger performance degradation: 25%, as mentioned by @Mark-Simulacrum.
This PR, for now, reverts #76244 and attempts to find out, which change caused the regression.