Cranelift: Break op cost ties with expression depth in egraphs #7456
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cfallin
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Nov 2, 2023
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a1phyr
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Nov 3, 2023
Mechanical change.
This means that, when the opcode cost is the same, we prefer shallow and wide expressions to narrow and deep. For example, `(a + b) + (c + d)` is preferred to `((a + b) + c) + d`. This is beneficial because it exposes more instruction-level parallelism and shortens live ranges. Co-Authored-By: Trevor Elliott <telliott@fastly.com>
Co-Authored-By: Chris Fallin <chris@cfallin.org> Co-Authored-By: Trevor Elliott <telliott@fastly.com>
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This means that, when the opcode cost is the same, we prefer shallow and wide
expressions to narrow and deep. For example,
(a + b) + (c + d)is preferred to((a + b) + c) + d. This is beneficial because it exposes moreinstruction-level parallelism and shortens live ranges.
Follow up PRs will add rules that take advantage of this.
Depends on #7465