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runtime: compute size classes statically

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No point in computing this info on startup.
Compute it at build time.
This lets us spend more time computing & checking the size classes.

Improve the div magic for rounding to the start of an object.
We can now use 32-bit multiplies & shifts, which should help
32-bit platforms.

The static data is <1KB.

The actual size classes are not changed by this CL.

Change-Id: I6450cec7d1b2b4ad31fd3f945f504ed2ec6570e7
Reviewed-on: https://go-review.googlesource.com/32219
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Austin Clements <austin@google.com>
This commit is contained in:
Keith Randall 2016-10-26 21:25:56 -07:00
parent 753caecc7e
commit 7ba36f4adb
6 changed files with 356 additions and 272 deletions
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4
src/runtime/mheap.go
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@ -234,7 +234,8 @@ type mspan struct {
// h->sweepgen is incremented by 2 after every GC
sweepgen uint32
divMul uint32 // for divide by elemsize - divMagic.mul
divMul uint16 // for divide by elemsize - divMagic.mul
baseMask uint16 // if non-0, elemsize is a power of 2, & this will get object allocation base
allocCount uint16 // capacity - number of objects in freelist
sizeclass uint8 // size class
incache bool // being used by an mcache
@ -248,7 +249,6 @@ type mspan struct {
limit uintptr // end of data in span
speciallock mutex // guards specials list
specials *special // linked list of special records sorted by offset.
baseMask uintptr // if non-0, elemsize is a power of 2, & this will get object allocation base
}
func (s *mspan) base() uintptr {