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Josh Bleecher Snyder c9591d73ef cmd/compile: eliminate some array equality alg loops
type T [3]string

Prior to this change, we generated this equality alg for T:

func eqT(p, q *T) (r bool) {
    for i := range *p {
        if len(p[i]) == len(q[i]) {
        } else {
            return
        }
    }
    for j := range *p {
        if runtime.memeq(p[j].ptr, q[j].ptr, len(p[j])) {
        } else {
            return
        }
    }
    return true
}

That first loop can be profitably eliminated;
it's cheaper to spell out 3 length equality checks.

We now generate:

func eqT(p, q *T) (r bool) {
    if len(p[0]) == len(q[0]) &&
        len(p[1]) == len(q[1]) &&
        len(p[2]) == len(q[2]) {
    } else {
        return
    }
    for i := 0; i < len(p); i++ {
        if runtime.memeq(p[j].ptr, q[j].ptr, len(p[j])) {
        } else {
            return
        }
    }
    return true
}

We now also eliminate loops for small float arrays as well,
and for any array of size 1.

These cutoffs were selected to minimize code size on amd64
at this moment, for lack of a more compelling methodology.
Any smallish number would do.

The switch from range loops to plain for loops allowed me
to use a temp instead of a named var, which eliminated
a pointless argument to checkAll.
The code to construct them is also a bit clearer, in my opinion.

Change-Id: I1bdd8ee4a2739d00806e66b17a4e76b46e71231a
Reviewed-on: https://go-review.googlesource.com/c/go/+/230210
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
2020-04-27 17:34:32 +00:00
.github .github: add link to questions in ISSUE_TEMPLATE 2020-01-06 17:05:31 +00:00
api all: remove scattered remnants of darwin/386 2020-04-08 18:37:38 +00:00
doc os, net: define and use os.ErrDeadlineExceeded 2020-04-25 00:26:48 +00:00
lib/time time/tzdata: new package 2020-04-14 19:34:31 +00:00
misc cmd/cgo: use consistent tag for a particular struct 2020-04-14 18:59:37 +00:00
src cmd/compile: eliminate some array equality alg loops 2020-04-27 17:34:32 +00:00
test cmd/compile: optimize Move with all-zero ro sym src to Zero 2020-04-24 23:58:10 +00:00
.gitattributes build: force all Windows batch files to CRLF 2020-03-22 08:42:38 +00:00
.gitignore .gitignore: ignore src/cmd/dist/dist 2017-10-28 21:55:49 +00:00
AUTHORS A: Qais Patankar (individual CLA) 2020-04-25 23:01:43 +00:00
CONTRIBUTING.md all: restore changes from faulty merge/revert 2018-02-12 20:13:59 +00:00
CONTRIBUTORS A+C: add Andy Pan (individual CLA) 2020-04-05 22:58:00 +00:00
favicon.ico website: recreate 16px and 32px favicon 2016-08-25 15:43:32 +00:00
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SECURITY.md SECURITY.md: update go versions 2019-09-26 15:34:57 +00:00

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