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cmd/compile: remove unused constant divide strength reduction code

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Change list https://golang.org/cl/37015/ moved the optimization
of division by constants to the generic ssa backend.
This removes the old now unused code that was used
for this optimization outside of the ssa backend.

Change-Id: I86223e56742e48dbb372ba8d779681e66448c513
Reviewed-on: https://go-review.googlesource.com/37198
Run-TryBot: Martin Möhrmann <moehrmann@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
Reviewed-by: Keith Randall <khr@golang.org>
This commit is contained in:
Martin Möhrmann 2017-02-19 11:34:29 +01:00
parent 177dfba112
commit 3892d50796
1 changed files with 0 additions and 220 deletions
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220
src/cmd/compile/internal/gc/magic.go
View File

@ -1,220 +0,0 @@
// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package gc
// Transmogrify slow integer division into fast multiplication using magic.
// argument passing to/from
// smagic and umagic
type Magic struct {
W int // input for both - width
S int // output for both - shift
Bad int // output for both - unexpected failure
// magic multiplier for signed literal divisors
Sd int64 // input - literal divisor
Sm int64 // output - multiplier
// magic multiplier for unsigned literal divisors
Ud uint64 // input - literal divisor
Um uint64 // output - multiplier
Ua int // output - adder
}
// magic number for signed division
// see hacker's delight chapter 10
func smagic(m *Magic) {
var mask uint64
m.Bad = 0
switch m.W {
default:
m.Bad = 1
return
case 8:
mask = 0xff
case 16:
mask = 0xffff
case 32:
mask = 0xffffffff
case 64:
mask = 0xffffffffffffffff
}
two31 := mask ^ (mask >> 1)
p := m.W - 1
ad := uint64(m.Sd)
if m.Sd < 0 {
ad = -uint64(m.Sd)
}
// bad denominators
if ad == 0 || ad == 1 || ad == two31 {
m.Bad = 1
return
}
t := two31
ad &= mask
anc := t - 1 - t%ad
anc &= mask
q1 := two31 / anc
r1 := two31 - q1*anc
q1 &= mask
r1 &= mask
q2 := two31 / ad
r2 := two31 - q2*ad
q2 &= mask
r2 &= mask
var delta uint64
for {
p++
q1 <<= 1
r1 <<= 1
q1 &= mask
r1 &= mask
if r1 >= anc {
q1++
r1 -= anc
q1 &= mask
r1 &= mask
}
q2 <<= 1
r2 <<= 1
q2 &= mask
r2 &= mask
if r2 >= ad {
q2++
r2 -= ad
q2 &= mask
r2 &= mask
}
delta = ad - r2
delta &= mask
if q1 < delta || (q1 == delta && r1 == 0) {
continue
}
break
}
m.Sm = int64(q2 + 1)
if uint64(m.Sm)&two31 != 0 {
m.Sm |= ^int64(mask)
}
m.S = p - m.W
}
// magic number for unsigned division
// see hacker's delight chapter 10
func umagic(m *Magic) {
var mask uint64
m.Bad = 0
m.Ua = 0
switch m.W {
default:
m.Bad = 1
return
case 8:
mask = 0xff
case 16:
mask = 0xffff
case 32:
mask = 0xffffffff
case 64:
mask = 0xffffffffffffffff
}
two31 := mask ^ (mask >> 1)
m.Ud &= mask
if m.Ud == 0 || m.Ud == two31 {
m.Bad = 1
return
}
nc := mask - (-m.Ud&mask)%m.Ud
p := m.W - 1
q1 := two31 / nc
r1 := two31 - q1*nc
q1 &= mask
r1 &= mask
q2 := (two31 - 1) / m.Ud
r2 := (two31 - 1) - q2*m.Ud
q2 &= mask
r2 &= mask
var delta uint64
for {
p++
if r1 >= nc-r1 {
q1 <<= 1
q1++
r1 <<= 1
r1 -= nc
} else {
q1 <<= 1
r1 <<= 1
}
q1 &= mask
r1 &= mask
if r2+1 >= m.Ud-r2 {
if q2 >= two31-1 {
m.Ua = 1
}
q2 <<= 1
q2++
r2 <<= 1
r2++
r2 -= m.Ud
} else {
if q2 >= two31 {
m.Ua = 1
}
q2 <<= 1
r2 <<= 1
r2++
}
q2 &= mask
r2 &= mask
delta = m.Ud - 1 - r2
delta &= mask
if p < m.W+m.W {
if q1 < delta || (q1 == delta && r1 == 0) {
continue
}
}
break
}
m.Um = q2 + 1
m.S = p - m.W
}