cmd/compile: overhaul inliner

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We’re starting a project to overhaul the inlining optimization pass in the Go compiler, with the goal of having a far more effective inliner in Go 1.22. This issue will track this work. This document motivates this project and outlines our general design goals. More detailed design documents will follow.

This project is being driven by @thanm and @mdempsky, but we would love to have input from the community. Inlining is inherently very heuristic and can be a deep rabbit hole to go down, so I’m sure many of our design decisions will be motivated by pragmatism and trying to ship something better than what we have for Go 1.22, even if it’s not perfect, with the goal of further improving it in later releases.

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Change https://go.dev/cl/511565 mentions this issue: cmd/compile/internal/inline: add call site flag generation

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Change https://go.dev/cl/511560 mentions this issue: cmd/compile/internal/ir: export 'reassigned', handle OASOP

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Change https://go.dev/cl/511559 mentions this issue: cmd/compile/internal/inline: analyze function return properties

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Change https://go.dev/cl/511555 mentions this issue: internal/goexperiment: add "InlinerRevamp" experiment

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Change https://go.dev/cl/511566 mentions this issue: cmd/compile/internal/inline/inlheur: assign scores to callsites

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Change https://go.dev/cl/511564 mentions this issue: cmd/compile/internal/inline: build call site table

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Change https://go.dev/cl/511562 mentions this issue: cmd/compile: write "properties" to export data for inlinable funcs

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Change https://go.dev/cl/511557 mentions this issue: cmd/compile/internal/inline: add framework to compute func "properties"

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Change https://go.dev/cl/511561 mentions this issue: cmd/compile/internal/inline: analyze function param properties