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[SR-2045] Optimization of FloatingPoint .round for Float/Double/Float80 #44654

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stephentyrone opened this issue Jul 11, 2016 · 7 comments
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[SR-2045] Optimization of FloatingPoint .round for Float/Double/Float80 #44654

stephentyrone opened this issue Jul 11, 2016 · 7 comments
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improvement standard library Area: Standard library umbrella

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Previous ID SR-2045
Radar None
Original Reporter @stephentyrone
Type Improvement
Status Closed
Resolution Done
Additional Detail from JIRA
Votes 0
Component/s Standard Library
Labels Improvement
Assignee @stephentyrone
Priority Medium

md5: 087779091399356b02a215851a43df40

Issue Description:

These functions contain an extra layer of indirection as currently implemented; they call e.g. `_swift_stdlib_ceilf( )`, which turns around and either calls `ceilf( )` or contains a lowering of `ceilf( )` (arm64).

This extra overhead is especially significant for these functions in particular because they have single-instruction implementations for `Float` and `Double` on arm64 and x86. We're eating a function call where we should simply have a single instruction instead.
@stephentyrone
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#3454

@xwu
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xwu commented Jul 11, 2016

Out of curiosity, is the same indirection also worth addressing for fused multiply-add and remainder?

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Yes, definitely (especially for FMA, remainder is relatively rare and expensive no matter what). I think there's a bug for that kicking around somewhere, but if there isn't I'll take a look.

@stephentyrone
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@xwu I threw fma and sqrt in with this change. Remainder requires more fiddling, and is much less important.

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xwu commented Jul 12, 2016

Thanks! I'd offer to pitch in, but one look at the plumbing in lib/AST/* and it's clear I don't have that skill.

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Found a solution for remainder too. No AST plumbing necessary.

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Done for Apple platforms. `squareRoot` and `remainder` will need special handling for Linux, but that can be done under a separate bug.

@swift-ci swift-ci transferred this issue from apple/swift-issues Apr 25, 2022
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