cmd/internal/obj: remove Follow pass

The Follow pass in the assembler backend reorders and copies
instructions. This even applies to hand-written assembly code,
which in many cases don't want to be reordered. Now that the
SSA compiler does a good job for laying out instructions, the
benefit of this pass is very little:

AMD64: (old = with Follow, new = without Follow)
name                      old time/op    new time/op    delta
BinaryTree17-12              2.78s ± 1%     2.79s ± 1%  +0.44%  (p=0.000 n=20+19)
Fannkuch11-12                3.11s ± 0%     3.31s ± 1%  +6.16%  (p=0.000 n=19+19)
FmtFprintfEmpty-12          50.9ns ± 1%    51.6ns ± 3%  +1.40%  (p=0.000 n=17+20)
FmtFprintfString-12          127ns ± 0%     128ns ± 1%  +0.88%  (p=0.000 n=17+17)
FmtFprintfInt-12             122ns ± 0%     123ns ± 1%  +0.76%  (p=0.000 n=20+19)
FmtFprintfIntInt-12          185ns ± 1%     186ns ± 1%  +0.65%  (p=0.000 n=20+19)
FmtFprintfPrefixedInt-12     192ns ± 1%     202ns ± 1%  +4.99%  (p=0.000 n=20+19)
FmtFprintfFloat-12           284ns ± 0%     288ns ± 0%  +1.33%  (p=0.000 n=15+19)
FmtManyArgs-12               807ns ± 0%     804ns ± 0%  -0.44%  (p=0.000 n=16+18)
GobDecode-12                7.23ms ± 1%    7.21ms ± 1%    ~     (p=0.052 n=20+20)
GobEncode-12                6.09ms ± 1%    6.12ms ± 1%  +0.41%  (p=0.002 n=19+19)
Gzip-12                      253ms ± 1%     255ms ± 1%  +0.95%  (p=0.000 n=18+20)
Gunzip-12                   38.4ms ± 0%    38.5ms ± 0%  +0.34%  (p=0.000 n=17+17)
HTTPClientServer-12         95.4µs ± 2%    96.1µs ± 1%  +0.78%  (p=0.002 n=19+19)
JSONEncode-12               16.5ms ± 1%    16.6ms ± 1%  +1.17%  (p=0.000 n=19+19)
JSONDecode-12               54.6ms ± 1%    55.3ms ± 1%  +1.23%  (p=0.000 n=18+18)
Mandelbrot200-12            4.47ms ± 0%    4.47ms ± 0%  +0.06%  (p=0.000 n=18+18)
GoParse-12                  3.47ms ± 1%    3.47ms ± 1%    ~     (p=0.583 n=20+20)
RegexpMatchEasy0_32-12      84.8ns ± 1%    85.2ns ± 2%  +0.51%  (p=0.022 n=20+20)
RegexpMatchEasy0_1K-12       206ns ± 1%     206ns ± 1%    ~     (p=0.770 n=20+20)
RegexpMatchEasy1_32-12      82.8ns ± 1%    83.4ns ± 1%  +0.64%  (p=0.000 n=20+19)
RegexpMatchEasy1_1K-12       363ns ± 1%     361ns ± 1%  -0.48%  (p=0.007 n=20+20)
RegexpMatchMedium_32-12      126ns ± 1%     126ns ± 0%  +0.72%  (p=0.000 n=20+20)
RegexpMatchMedium_1K-12     39.1µs ± 1%    39.8µs ± 0%  +1.73%  (p=0.000 n=19+19)
RegexpMatchHard_32-12       1.97µs ± 0%    1.98µs ± 1%  +0.29%  (p=0.005 n=18+20)
RegexpMatchHard_1K-12       59.5µs ± 1%    59.8µs ± 1%  +0.36%  (p=0.000 n=18+20)
Revcomp-12                   442ms ± 1%     445ms ± 2%  +0.67%  (p=0.000 n=19+20)
Template-12                 58.0ms ± 1%    57.5ms ± 1%  -0.85%  (p=0.000 n=19+19)
TimeParse-12                 311ns ± 0%     314ns ± 0%  +0.94%  (p=0.000 n=20+18)
TimeFormat-12                350ns ± 3%     346ns ± 0%    ~     (p=0.076 n=20+19)
[Geo mean]                  55.9µs         56.4µs       +0.80%

ARM32:
name                     old time/op    new time/op    delta
BinaryTree17-4              30.4s ± 0%     30.1s ± 0%  -1.14%  (p=0.000 n=10+8)
Fannkuch11-4                13.7s ± 0%     13.6s ± 0%  -0.75%  (p=0.000 n=10+10)
FmtFprintfEmpty-4           664ns ± 1%     651ns ± 1%  -1.96%  (p=0.000 n=7+8)
FmtFprintfString-4         1.83µs ± 2%    1.77µs ± 2%  -3.21%  (p=0.000 n=10+10)
FmtFprintfInt-4            1.57µs ± 2%    1.54µs ± 2%  -2.25%  (p=0.007 n=10+10)
FmtFprintfIntInt-4         2.37µs ± 2%    2.31µs ± 1%  -2.68%  (p=0.000 n=10+10)
FmtFprintfPrefixedInt-4    2.14µs ± 2%    2.10µs ± 1%  -1.83%  (p=0.006 n=10+10)
FmtFprintfFloat-4          3.69µs ± 2%    3.74µs ± 1%  +1.60%  (p=0.000 n=10+10)
FmtManyArgs-4              9.43µs ± 1%    9.17µs ± 1%  -2.70%  (p=0.000 n=10+10)
GobDecode-4                76.3ms ± 1%    75.5ms ± 1%  -1.14%  (p=0.003 n=10+10)
GobEncode-4                70.7ms ± 2%    69.0ms ± 1%  -2.36%  (p=0.000 n=10+10)
Gzip-4                      2.64s ± 1%     2.65s ± 0%  +0.59%  (p=0.002 n=10+10)
Gunzip-4                    402ms ± 0%     398ms ± 0%  -1.11%  (p=0.000 n=10+9)
HTTPClientServer-4          458µs ± 0%     457µs ± 0%    ~     (p=0.247 n=10+10)
JSONEncode-4                171ms ± 0%     172ms ± 0%  +0.56%  (p=0.000 n=10+10)
JSONDecode-4                672ms ± 1%     668ms ± 1%    ~     (p=0.105 n=10+10)
Mandelbrot200-4            33.5ms ± 0%    33.5ms ± 0%    ~     (p=0.156 n=9+10)
GoParse-4                  33.9ms ± 0%    34.0ms ± 0%  +0.36%  (p=0.031 n=9+9)
RegexpMatchEasy0_32-4       823ns ± 1%     835ns ± 1%  +1.49%  (p=0.000 n=8+8)
RegexpMatchEasy0_1K-4      3.99µs ± 0%    4.02µs ± 1%  +0.92%  (p=0.000 n=8+10)
RegexpMatchEasy1_32-4       877ns ± 3%     904ns ± 2%  +3.07%  (p=0.012 n=10+10)
RegexpMatchEasy1_1K-4      5.99µs ± 0%    5.97µs ± 1%  -0.38%  (p=0.023 n=8+8)
RegexpMatchMedium_32-4     1.40µs ± 2%    1.40µs ± 2%    ~     (p=0.590 n=10+9)
RegexpMatchMedium_1K-4      357µs ± 0%     355µs ± 1%  -0.72%  (p=0.000 n=7+8)
RegexpMatchHard_32-4       22.3µs ± 0%    22.1µs ± 0%  -0.49%  (p=0.000 n=8+7)
RegexpMatchHard_1K-4        661µs ± 0%     658µs ± 0%  -0.42%  (p=0.000 n=8+7)
Revcomp-4                  46.3ms ± 0%    46.3ms ± 0%    ~     (p=0.393 n=10+10)
Template-4                  753ms ± 1%     750ms ± 0%    ~     (p=0.211 n=10+9)
TimeParse-4                4.28µs ± 1%    4.22µs ± 1%  -1.34%  (p=0.000 n=8+10)
TimeFormat-4               9.00µs ± 0%    9.05µs ± 0%  +0.59%  (p=0.000 n=10+10)
[Geo mean]                  538µs          535µs       -0.55%

ARM64:
name                     old time/op    new time/op    delta
BinaryTree17-8              8.39s ± 0%     8.39s ± 0%    ~     (p=0.684 n=10+10)
Fannkuch11-8                5.95s ± 0%     5.99s ± 0%  +0.63%  (p=0.000 n=10+10)
FmtFprintfEmpty-8           116ns ± 0%     116ns ± 0%    ~     (all equal)
FmtFprintfString-8          361ns ± 0%     360ns ± 0%  -0.31%  (p=0.003 n=8+6)
FmtFprintfInt-8             290ns ± 0%     290ns ± 0%    ~     (p=0.620 n=9+9)
FmtFprintfIntInt-8          476ns ± 1%     469ns ± 0%  -1.47%  (p=0.000 n=10+6)
FmtFprintfPrefixedInt-8     412ns ± 2%     417ns ± 2%  +1.39%  (p=0.006 n=9+10)
FmtFprintfFloat-8           652ns ± 1%     652ns ± 0%    ~     (p=0.161 n=10+8)
FmtManyArgs-8              1.94µs ± 0%    1.94µs ± 2%    ~     (p=0.781 n=10+10)
GobDecode-8                17.7ms ± 1%    17.7ms ± 0%    ~     (p=0.962 n=10+7)
GobEncode-8                15.6ms ± 0%    15.6ms ± 1%    ~     (p=0.063 n=10+10)
Gzip-8                      786ms ± 0%     787ms ± 0%    ~     (p=0.356 n=10+9)
Gunzip-8                    127ms ± 0%     127ms ± 0%  +0.08%  (p=0.028 n=10+9)
HTTPClientServer-8          198µs ± 6%     198µs ± 7%    ~     (p=0.796 n=10+10)
JSONEncode-8               42.5ms ± 0%    42.2ms ± 0%  -0.73%  (p=0.000 n=9+8)
JSONDecode-8                158ms ± 1%     162ms ± 0%  +2.28%  (p=0.000 n=10+9)
Mandelbrot200-8            10.1ms ± 0%    10.1ms ± 0%  -0.01%  (p=0.000 n=10+9)
GoParse-8                  8.54ms ± 1%    8.63ms ± 1%  +1.06%  (p=0.000 n=10+9)
RegexpMatchEasy0_32-8       231ns ± 1%     225ns ± 0%  -2.52%  (p=0.000 n=9+10)
RegexpMatchEasy0_1K-8      1.63µs ± 0%    1.63µs ± 0%    ~     (p=0.170 n=10+10)
RegexpMatchEasy1_32-8       253ns ± 0%     249ns ± 0%  -1.41%  (p=0.000 n=9+10)
RegexpMatchEasy1_1K-8      2.08µs ± 0%    2.08µs ± 0%  -0.32%  (p=0.000 n=9+10)
RegexpMatchMedium_32-8      355ns ± 1%     351ns ± 0%  -1.04%  (p=0.007 n=10+7)
RegexpMatchMedium_1K-8      104µs ± 0%     104µs ± 0%    ~     (p=0.148 n=10+10)
RegexpMatchHard_32-8       5.79µs ± 0%    5.79µs ± 0%    ~     (p=0.578 n=10+10)
RegexpMatchHard_1K-8        176µs ± 0%     176µs ± 0%    ~     (p=0.137 n=10+10)
Revcomp-8                   1.37s ± 1%     1.36s ± 1%  -0.26%  (p=0.023 n=10+10)
Template-8                  151ms ± 1%     154ms ± 1%  +2.14%  (p=0.000 n=9+10)
TimeParse-8                 723ns ± 2%     721ns ± 1%    ~     (p=0.592 n=10+10)
TimeFormat-8                804ns ± 2%     798ns ± 3%    ~     (p=0.344 n=10+10)
[Geo mean]                  154µs          154µs       -0.02%

Therefore remove this pass. Also reduce text size by 0.5~2%.

Comment out some dead code in runtime/sys_nacl_amd64p32.s
which contains undefined symbols.

Change-Id: I1473986fe5b18b3d2554ce96cdc6f0999b8d955d
Reviewed-on: https://go-review.googlesource.com/36205
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

8 files changed, 0 insertions, 1092 deletions

diff --git a/src/cmd/internal/obj/arm/obj5.go b/src/cmd/internal/obj/arm/obj5.go
index 0bf8014398..75d22bcf81 100644
--- a/src/cmd/internal/obj/arm/obj5.go
+++ b/src/cmd/internal/obj/arm/obj5.go
@@ -34,7 +34,6 @@ import (
 	"cmd/internal/obj"
 	"cmd/internal/sys"
 	"fmt"
-	"log"
 	"math"
 )
 
@@ -862,183 +861,6 @@ func initdiv(ctxt *obj.Link) {
 	ctxt.Sym_modu = obj.Linklookup(ctxt, "_modu", 0)
 }
 
-func follow(ctxt *obj.Link, s *obj.LSym) {
-	ctxt.Cursym = s
-
-	firstp := ctxt.NewProg()
-	lastp := firstp
-	xfol(ctxt, s.Text, &lastp)
-	lastp.Link = nil
-	s.Text = firstp.Link
-}
-
-func relinv(a obj.As) obj.As {
-	switch a {
-	case ABEQ:
-		return ABNE
-	case ABNE:
-		return ABEQ
-	case ABCS:
-		return ABCC
-	case ABHS:
-		return ABLO
-	case ABCC:
-		return ABCS
-	case ABLO:
-		return ABHS
-	case ABMI:
-		return ABPL
-	case ABPL:
-		return ABMI
-	case ABVS:
-		return ABVC
-	case ABVC:
-		return ABVS
-	case ABHI:
-		return ABLS
-	case ABLS:
-		return ABHI
-	case ABGE:
-		return ABLT
-	case ABLT:
-		return ABGE
-	case ABGT:
-		return ABLE
-	case ABLE:
-		return ABGT
-	}
-
-	log.Fatalf("unknown relation: %s", Anames[a])
-	return 0
-}
-
-func xfol(ctxt *obj.Link, p *obj.Prog, last **obj.Prog) {
-	var q *obj.Prog
-	var r *obj.Prog
-	var i int
-
-loop:
-	if p == nil {
-		return
-	}
-	a := p.As
-	if a == AB {
-		q = p.Pcond
-		if q != nil && q.As != obj.ATEXT {
-			p.Mark |= FOLL
-			p = q
-			if p.Mark&FOLL == 0 {
-				goto loop
-			}
-		}
-	}
-
-	if p.Mark&FOLL != 0 {
-		i = 0
-		q = p
-		for ; i < 4; i, q = i+1, q.Link {
-			if q == *last || q == nil {
-				break
-			}
-			a = q.As
-			if a == obj.ANOP {
-				i--
-				continue
-			}
-
-			if a == AB || (a == obj.ARET && q.Scond == C_SCOND_NONE) || a == ARFE || a == obj.AUNDEF {
-				goto copy
-			}
-			if q.Pcond == nil || (q.Pcond.Mark&FOLL != 0) {
-				continue
-			}
-			if a != ABEQ && a != ABNE {
-				continue
-			}
-
-		copy:
-			for {
-				r = ctxt.NewProg()
-				*r = *p
-				if r.Mark&FOLL == 0 {
-					fmt.Printf("can't happen 1\n")
-				}
-				r.Mark |= FOLL
-				if p != q {
-					p = p.Link
-					(*last).Link = r
-					*last = r
-					continue
-				}
-
-				(*last).Link = r
-				*last = r
-				if a == AB || (a == obj.ARET && q.Scond == C_SCOND_NONE) || a == ARFE || a == obj.AUNDEF {
-					return
-				}
-				r.As = ABNE
-				if a == ABNE {
-					r.As = ABEQ
-				}
-				r.Pcond = p.Link
-				r.Link = p.Pcond
-				if r.Link.Mark&FOLL == 0 {
-					xfol(ctxt, r.Link, last)
-				}
-				if r.Pcond.Mark&FOLL == 0 {
-					fmt.Printf("can't happen 2\n")
-				}
-				return
-			}
-		}
-
-		a = AB
-		q = ctxt.NewProg()
-		q.As = a
-		q.Pos = p.Pos
-		q.To.Type = obj.TYPE_BRANCH
-		q.To.Offset = p.Pc
-		q.Pcond = p
-		p = q
-	}
-
-	p.Mark |= FOLL
-	(*last).Link = p
-	*last = p
-	if a == AB || (a == obj.ARET && p.Scond == C_SCOND_NONE) || a == ARFE || a == obj.AUNDEF {
-		return
-	}
-
-	if p.Pcond != nil {
-		if a != ABL && a != ABX && p.Link != nil {
-			q = obj.Brchain(ctxt, p.Link)
-			if a != obj.ATEXT {
-				if q != nil && (q.Mark&FOLL != 0) {
-					p.As = relinv(a)
-					p.Link = p.Pcond
-					p.Pcond = q
-				}
-			}
-
-			xfol(ctxt, p.Link, last)
-			q = obj.Brchain(ctxt, p.Pcond)
-			if q == nil {
-				q = p.Pcond
-			}
-			if q.Mark&FOLL != 0 {
-				p.Pcond = q
-				return
-			}
-
-			p = q
-			goto loop
-		}
-	}
-
-	p = p.Link
-	goto loop
-}
-
 var unaryDst = map[obj.As]bool{
 	ASWI:  true,
 	AWORD: true,
@@ -1048,7 +870,6 @@ var Linkarm = obj.LinkArch{
 	Arch:       sys.ArchARM,
 	Preprocess: preprocess,
 	Assemble:   span5,
-	Follow:     follow,
 	Progedit:   progedit,
 	UnaryDst:   unaryDst,
 }
diff --git a/src/cmd/internal/obj/arm64/obj7.go b/src/cmd/internal/obj/arm64/obj7.go
index f70ca345ed..f68964ab49 100644
--- a/src/cmd/internal/obj/arm64/obj7.go
+++ b/src/cmd/internal/obj/arm64/obj7.go
@@ -34,7 +34,6 @@ import (
 	"cmd/internal/obj"
 	"cmd/internal/sys"
 	"fmt"
-	"log"
 	"math"
 )
 
@@ -443,191 +442,6 @@ func rewriteToUseGot(ctxt *obj.Link, p *obj.Prog) {
 	obj.Nopout(p)
 }
 
-func follow(ctxt *obj.Link, s *obj.LSym) {
-	ctxt.Cursym = s
-
-	firstp := ctxt.NewProg()
-	lastp := firstp
-	xfol(ctxt, s.Text, &lastp)
-	lastp.Link = nil
-	s.Text = firstp.Link
-}
-
-func relinv(a obj.As) obj.As {
-	switch a {
-	case ABEQ:
-		return ABNE
-	case ABNE:
-		return ABEQ
-	case ABCS:
-		return ABCC
-	case ABHS:
-		return ABLO
-	case ABCC:
-		return ABCS
-	case ABLO:
-		return ABHS
-	case ABMI:
-		return ABPL
-	case ABPL:
-		return ABMI
-	case ABVS:
-		return ABVC
-	case ABVC:
-		return ABVS
-	case ABHI:
-		return ABLS
-	case ABLS:
-		return ABHI
-	case ABGE:
-		return ABLT
-	case ABLT:
-		return ABGE
-	case ABGT:
-		return ABLE
-	case ABLE:
-		return ABGT
-	case ACBZ:
-		return ACBNZ
-	case ACBNZ:
-		return ACBZ
-	case ACBZW:
-		return ACBNZW
-	case ACBNZW:
-		return ACBZW
-	}
-
-	log.Fatalf("unknown relation: %s", Anames[a-obj.ABaseARM64])
-	return 0
-}
-
-func xfol(ctxt *obj.Link, p *obj.Prog, last **obj.Prog) {
-	var q *obj.Prog
-	var r *obj.Prog
-	var i int
-
-loop:
-	if p == nil {
-		return
-	}
-	a := p.As
-	if a == AB {
-		q = p.Pcond
-		if q != nil {
-			p.Mark |= FOLL
-			p = q
-			if !(p.Mark&FOLL != 0) {
-				goto loop
-			}
-		}
-	}
-
-	if p.Mark&FOLL != 0 {
-		i = 0
-		q = p
-		for ; i < 4; i, q = i+1, q.Link {
-			if q == *last || q == nil {
-				break
-			}
-			a = q.As
-			if a == obj.ANOP {
-				i--
-				continue
-			}
-
-			if a == AB || a == obj.ARET || a == AERET {
-				goto copy
-			}
-			if q.Pcond == nil || (q.Pcond.Mark&FOLL != 0) {
-				continue
-			}
-			if a != ABEQ && a != ABNE {
-				continue
-			}
-
-		copy:
-			for {
-				r = ctxt.NewProg()
-				*r = *p
-				if !(r.Mark&FOLL != 0) {
-					fmt.Printf("can't happen 1\n")
-				}
-				r.Mark |= FOLL
-				if p != q {
-					p = p.Link
-					(*last).Link = r
-					*last = r
-					continue
-				}
-
-				(*last).Link = r
-				*last = r
-				if a == AB || a == obj.ARET || a == AERET {
-					return
-				}
-				if a == ABNE {
-					r.As = ABEQ
-				} else {
-					r.As = ABNE
-				}
-				r.Pcond = p.Link
-				r.Link = p.Pcond
-				if !(r.Link.Mark&FOLL != 0) {
-					xfol(ctxt, r.Link, last)
-				}
-				if !(r.Pcond.Mark&FOLL != 0) {
-					fmt.Printf("can't happen 2\n")
-				}
-				return
-			}
-		}
-
-		a = AB
-		q = ctxt.NewProg()
-		q.As = a
-		q.Pos = p.Pos
-		q.To.Type = obj.TYPE_BRANCH
-		q.To.Offset = p.Pc
-		q.Pcond = p
-		p = q
-	}
-
-	p.Mark |= FOLL
-	(*last).Link = p
-	*last = p
-	if a == AB || a == obj.ARET || a == AERET {
-		return
-	}
-	if p.Pcond != nil {
-		if a != ABL && p.Link != nil {
-			q = obj.Brchain(ctxt, p.Link)
-			if a != obj.ATEXT {
-				if q != nil && (q.Mark&FOLL != 0) {
-					p.As = relinv(a)
-					p.Link = p.Pcond
-					p.Pcond = q
-				}
-			}
-
-			xfol(ctxt, p.Link, last)
-			q = obj.Brchain(ctxt, p.Pcond)
-			if q == nil {
-				q = p.Pcond
-			}
-			if q.Mark&FOLL != 0 {
-				p.Pcond = q
-				return
-			}
-
-			p = q
-			goto loop
-		}
-	}
-
-	p = p.Link
-	goto loop
-}
-
 func preprocess(ctxt *obj.Link, cursym *obj.LSym) {
 	ctxt.Cursym = cursym
 
@@ -998,7 +812,6 @@ var Linkarm64 = obj.LinkArch{
 	Arch:       sys.ArchARM64,
 	Preprocess: preprocess,
 	Assemble:   span7,
-	Follow:     follow,
 	Progedit:   progedit,
 	UnaryDst:   unaryDst,
 }
diff --git a/src/cmd/internal/obj/link.go b/src/cmd/internal/obj/link.go
index ffc7a1b25b..1d2d03593d 100644
--- a/src/cmd/internal/obj/link.go
+++ b/src/cmd/internal/obj/link.go
@@ -804,7 +804,6 @@ type LinkArch struct {
 	*sys.Arch
 	Preprocess func(*Link, *LSym)
 	Assemble   func(*Link, *LSym)
-	Follow     func(*Link, *LSym)
 	Progedit   func(*Link, *Prog)
 	UnaryDst   map[As]bool // Instruction takes one operand, a destination.
 }
diff --git a/src/cmd/internal/obj/mips/obj0.go b/src/cmd/internal/obj/mips/obj0.go
index 87ddcd2bb3..097b834e49 100644
--- a/src/cmd/internal/obj/mips/obj0.go
+++ b/src/cmd/internal/obj/mips/obj0.go
@@ -1418,151 +1418,10 @@ func compound(ctxt *obj.Link, p *obj.Prog) bool {
 	return false
 }
 
-func follow(ctxt *obj.Link, s *obj.LSym) {
-	ctxt.Cursym = s
-
-	firstp := ctxt.NewProg()
-	lastp := firstp
-	xfol(ctxt, s.Text, &lastp)
-	lastp.Link = nil
-	s.Text = firstp.Link
-}
-
-func xfol(ctxt *obj.Link, p *obj.Prog, last **obj.Prog) {
-	var q *obj.Prog
-	var r *obj.Prog
-	var i int
-
-loop:
-	if p == nil {
-		return
-	}
-	a := p.As
-	if a == AJMP {
-		q = p.Pcond
-		if (p.Mark&NOSCHED != 0) || q != nil && (q.Mark&NOSCHED != 0) {
-			p.Mark |= FOLL
-			(*last).Link = p
-			*last = p
-			p = p.Link
-			xfol(ctxt, p, last)
-			p = q
-			if p != nil && p.Mark&FOLL == 0 {
-				goto loop
-			}
-			return
-		}
-
-		if q != nil {
-			p.Mark |= FOLL
-			p = q
-			if p.Mark&FOLL == 0 {
-				goto loop
-			}
-		}
-	}
-
-	if p.Mark&FOLL != 0 {
-		i = 0
-		q = p
-		for ; i < 4; i, q = i+1, q.Link {
-			if q == *last || (q.Mark&NOSCHED != 0) {
-				break
-			}
-			a = q.As
-			if a == obj.ANOP {
-				i--
-				continue
-			}
-
-			if a == AJMP || a == ARET || a == ARFE {
-				goto copy
-			}
-			if q.Pcond == nil || (q.Pcond.Mark&FOLL != 0) {
-				continue
-			}
-			if a != ABEQ && a != ABNE {
-				continue
-			}
-
-		copy:
-			for {
-				r = ctxt.NewProg()
-				*r = *p
-				if r.Mark&FOLL == 0 {
-					fmt.Printf("can't happen 1\n")
-				}
-				r.Mark |= FOLL
-				if p != q {
-					p = p.Link
-					(*last).Link = r
-					*last = r
-					continue
-				}
-
-				(*last).Link = r
-				*last = r
-				if a == AJMP || a == ARET || a == ARFE {
-					return
-				}
-				r.As = ABNE
-				if a == ABNE {
-					r.As = ABEQ
-				}
-				r.Pcond = p.Link
-				r.Link = p.Pcond
-				if r.Link.Mark&FOLL == 0 {
-					xfol(ctxt, r.Link, last)
-				}
-				if r.Pcond.Mark&FOLL == 0 {
-					fmt.Printf("can't happen 2\n")
-				}
-				return
-			}
-		}
-
-		a = AJMP
-		q = ctxt.NewProg()
-		q.As = a
-		q.Pos = p.Pos
-		q.To.Type = obj.TYPE_BRANCH
-		q.To.Offset = p.Pc
-		q.Pcond = p
-		p = q
-	}
-
-	p.Mark |= FOLL
-	(*last).Link = p
-	*last = p
-	if a == AJMP || a == ARET || a == ARFE {
-		if p.Mark&NOSCHED != 0 {
-			p = p.Link
-			goto loop
-		}
-
-		return
-	}
-
-	if p.Pcond != nil {
-		if a != AJAL && p.Link != nil {
-			xfol(ctxt, p.Link, last)
-			p = p.Pcond
-			if p == nil || (p.Mark&FOLL != 0) {
-				return
-			}
-			goto loop
-		}
-	}
-
-	p = p.Link
-	goto loop
-}
-
 var Linkmips64 = obj.LinkArch{
 	Arch:       sys.ArchMIPS64,
 	Preprocess: preprocess,
 	Assemble:   span0,
-	Follow:     follow,
 	Progedit:   progedit,
 }
 
@@ -1570,7 +1429,6 @@ var Linkmips64le = obj.LinkArch{
 	Arch:       sys.ArchMIPS64LE,
 	Preprocess: preprocess,
 	Assemble:   span0,
-	Follow:     follow,
 	Progedit:   progedit,
 }
 
@@ -1578,7 +1436,6 @@ var Linkmips = obj.LinkArch{
 	Arch:       sys.ArchMIPS,
 	Preprocess: preprocess,
 	Assemble:   span0,
-	Follow:     follow,
 	Progedit:   progedit,
 }
 
@@ -1586,6 +1443,5 @@ var Linkmipsle = obj.LinkArch{
 	Arch:       sys.ArchMIPSLE,
 	Preprocess: preprocess,
 	Assemble:   span0,
-	Follow:     follow,
 	Progedit:   progedit,
 }
diff --git a/src/cmd/internal/obj/plist.go b/src/cmd/internal/obj/plist.go
index 804ea637b3..643f9d02c0 100644
--- a/src/cmd/internal/obj/plist.go
+++ b/src/cmd/internal/obj/plist.go
@@ -159,9 +159,6 @@ func flushplist(ctxt *Link, freeProgs bool) {
 	for _, s := range text {
 		mkfwd(s)
 		linkpatch(ctxt, s)
-		if ctxt.Flag_optimize {
-			ctxt.Arch.Follow(ctxt, s)
-		}
 		ctxt.Arch.Preprocess(ctxt, s)
 		ctxt.Arch.Assemble(ctxt, s)
 		fieldtrack(ctxt, s)
diff --git a/src/cmd/internal/obj/ppc64/obj9.go b/src/cmd/internal/obj/ppc64/obj9.go
index b328781d87..7668ddd1fc 100644
--- a/src/cmd/internal/obj/ppc64/obj9.go
+++ b/src/cmd/internal/obj/ppc64/obj9.go
@@ -1067,177 +1067,10 @@ func stacksplit(ctxt *obj.Link, p *obj.Prog, framesize int32) *obj.Prog {
 	return p
 }
 
-func follow(ctxt *obj.Link, s *obj.LSym) {
-	ctxt.Cursym = s
-
-	firstp := ctxt.NewProg()
-	lastp := firstp
-	xfol(ctxt, s.Text, &lastp)
-	lastp.Link = nil
-	s.Text = firstp.Link
-}
-
-func relinv(a obj.As) obj.As {
-	switch a {
-	case ABEQ:
-		return ABNE
-	case ABNE:
-		return ABEQ
-
-	case ABGE:
-		return ABLT
-	case ABLT:
-		return ABGE
-
-	case ABGT:
-		return ABLE
-	case ABLE:
-		return ABGT
-
-	case ABVC:
-		return ABVS
-	case ABVS:
-		return ABVC
-	}
-
-	return 0
-}
-
-func xfol(ctxt *obj.Link, p *obj.Prog, last **obj.Prog) {
-	var q *obj.Prog
-	var r *obj.Prog
-	var b obj.As
-	var i int
-
-loop:
-	if p == nil {
-		return
-	}
-	a := p.As
-	if a == ABR {
-		q = p.Pcond
-		if (p.Mark&NOSCHED != 0) || q != nil && (q.Mark&NOSCHED != 0) {
-			p.Mark |= FOLL
-			(*last).Link = p
-			*last = p
-			p = p.Link
-			xfol(ctxt, p, last)
-			p = q
-			if p != nil && p.Mark&FOLL == 0 {
-				goto loop
-			}
-			return
-		}
-
-		if q != nil {
-			p.Mark |= FOLL
-			p = q
-			if p.Mark&FOLL == 0 {
-				goto loop
-			}
-		}
-	}
-
-	if p.Mark&FOLL != 0 {
-		i = 0
-		q = p
-		for ; i < 4; i, q = i+1, q.Link {
-			if q == *last || (q.Mark&NOSCHED != 0) {
-				break
-			}
-			b = 0 /* set */
-			a = q.As
-			if a == obj.ANOP {
-				i--
-				continue
-			}
-
-			if a == ABR || a == obj.ARET || a == ARFI || a == ARFCI || a == ARFID || a == AHRFID {
-				goto copy
-			}
-			if q.Pcond == nil || (q.Pcond.Mark&FOLL != 0) {
-				continue
-			}
-			b = relinv(a)
-			if b == 0 {
-				continue
-			}
-
-		copy:
-			for {
-				r = ctxt.NewProg()
-				*r = *p
-				if r.Mark&FOLL == 0 {
-					fmt.Printf("can't happen 1\n")
-				}
-				r.Mark |= FOLL
-				if p != q {
-					p = p.Link
-					(*last).Link = r
-					*last = r
-					continue
-				}
-
-				(*last).Link = r
-				*last = r
-				if a == ABR || a == obj.ARET || a == ARFI || a == ARFCI || a == ARFID || a == AHRFID {
-					return
-				}
-				r.As = b
-				r.Pcond = p.Link
-				r.Link = p.Pcond
-				if r.Link.Mark&FOLL == 0 {
-					xfol(ctxt, r.Link, last)
-				}
-				if r.Pcond.Mark&FOLL == 0 {
-					fmt.Printf("can't happen 2\n")
-				}
-				return
-			}
-		}
-
-		a = ABR
-		q = ctxt.NewProg()
-		q.As = a
-		q.Pos = p.Pos
-		q.To.Type = obj.TYPE_BRANCH
-		q.To.Offset = p.Pc
-		q.Pcond = p
-		p = q
-	}
-
-	p.Mark |= FOLL
-	(*last).Link = p
-	*last = p
-	if a == ABR || a == obj.ARET || a == ARFI || a == ARFCI || a == ARFID || a == AHRFID {
-		if p.Mark&NOSCHED != 0 {
-			p = p.Link
-			goto loop
-		}
-
-		return
-	}
-
-	if p.Pcond != nil {
-		if a != ABL && p.Link != nil {
-			xfol(ctxt, p.Link, last)
-			p = p.Pcond
-			if p == nil || (p.Mark&FOLL != 0) {
-				return
-			}
-			goto loop
-		}
-	}
-
-	p = p.Link
-	goto loop
-}
-
 var Linkppc64 = obj.LinkArch{
 	Arch:       sys.ArchPPC64,
 	Preprocess: preprocess,
 	Assemble:   span9,
-	Follow:     follow,
 	Progedit:   progedit,
 }
 
@@ -1245,6 +1078,5 @@ var Linkppc64le = obj.LinkArch{
 	Arch:       sys.ArchPPC64LE,
 	Preprocess: preprocess,
 	Assemble:   span9,
-	Follow:     follow,
 	Progedit:   progedit,
 }
diff --git a/src/cmd/internal/obj/s390x/objz.go b/src/cmd/internal/obj/s390x/objz.go
index 86af775aad..9d2d931af1 100644
--- a/src/cmd/internal/obj/s390x/objz.go
+++ b/src/cmd/internal/obj/s390x/objz.go
@@ -837,176 +837,6 @@ func stacksplitPost(ctxt *obj.Link, p *obj.Prog, pPre *obj.Prog, pPreempt *obj.P
 	return p
 }
 
-var pc_cnt int64
-
-func follow(ctxt *obj.Link, s *obj.LSym) {
-	ctxt.Cursym = s
-
-	pc_cnt = 0
-	firstp := ctxt.NewProg()
-	lastp := firstp
-	xfol(ctxt, s.Text, &lastp)
-	lastp.Link = nil
-	s.Text = firstp.Link
-}
-
-func relinv(a obj.As) obj.As {
-	switch a {
-	case ABEQ:
-		return ABNE
-	case ABNE:
-		return ABEQ
-
-	case ABGE:
-		return ABLT
-	case ABLT:
-		return ABGE
-
-	case ABGT:
-		return ABLE
-	case ABLE:
-		return ABGT
-
-	case ABVC:
-		return ABVS
-	case ABVS:
-		return ABVC
-	}
-
-	return 0
-}
-
-func xfol(ctxt *obj.Link, p *obj.Prog, last **obj.Prog) {
-	var q *obj.Prog
-	var r *obj.Prog
-	var b obj.As
-
-	for p != nil {
-		a := p.As
-		if a == ABR {
-			q = p.Pcond
-			if (p.Mark&NOSCHED != 0) || q != nil && (q.Mark&NOSCHED != 0) {
-				p.Mark |= FOLL
-				(*last).Link = p
-				*last = p
-				(*last).Pc = pc_cnt
-				pc_cnt += 1
-				p = p.Link
-				xfol(ctxt, p, last)
-				p = q
-				if p != nil && p.Mark&FOLL == 0 {
-					continue
-				}
-				return
-			}
-
-			if q != nil {
-				p.Mark |= FOLL
-				p = q
-				if p.Mark&FOLL == 0 {
-					continue
-				}
-			}
-		}
-
-		if p.Mark&FOLL != 0 {
-			q = p
-			for i := 0; i < 4; i, q = i+1, q.Link {
-				if q == *last || (q.Mark&NOSCHED != 0) {
-					break
-				}
-				b = 0 /* set */
-				a = q.As
-				if a == obj.ANOP {
-					i--
-					continue
-				}
-				if a != ABR && a != obj.ARET {
-					if q.Pcond == nil || (q.Pcond.Mark&FOLL != 0) {
-						continue
-					}
-					b = relinv(a)
-					if b == 0 {
-						continue
-					}
-				}
-
-				for {
-					r = ctxt.NewProg()
-					*r = *p
-					if r.Mark&FOLL == 0 {
-						fmt.Printf("can't happen 1\n")
-					}
-					r.Mark |= FOLL
-					if p != q {
-						p = p.Link
-						(*last).Link = r
-						*last = r
-						(*last).Pc = pc_cnt
-						pc_cnt += 1
-						continue
-					}
-
-					(*last).Link = r
-					*last = r
-					(*last).Pc = pc_cnt
-					pc_cnt += 1
-					if a == ABR || a == obj.ARET {
-						return
-					}
-					r.As = b
-					r.Pcond = p.Link
-					r.Link = p.Pcond
-					if r.Link.Mark&FOLL == 0 {
-						xfol(ctxt, r.Link, last)
-					}
-					if r.Pcond.Mark&FOLL == 0 {
-						fmt.Printf("can't happen 2\n")
-					}
-					return
-				}
-			}
-
-			a = ABR
-			q = ctxt.NewProg()
-			q.As = a
-			q.Pos = p.Pos
-			q.To.Type = obj.TYPE_BRANCH
-			q.To.Offset = p.Pc
-			q.Pcond = p
-			p = q
-		}
-
-		p.Mark |= FOLL
-		(*last).Link = p
-		*last = p
-		(*last).Pc = pc_cnt
-		pc_cnt += 1
-
-		if a == ABR || a == obj.ARET {
-			if p.Mark&NOSCHED != 0 {
-				p = p.Link
-				continue
-			}
-
-			return
-		}
-
-		if p.Pcond != nil {
-			if a != ABL && p.Link != nil {
-				xfol(ctxt, p.Link, last)
-				p = p.Pcond
-				if p == nil || (p.Mark&FOLL != 0) {
-					return
-				}
-				continue
-			}
-		}
-
-		p = p.Link
-	}
-}
-
 var unaryDst = map[obj.As]bool{
 	ASTCK:  true,
 	ASTCKC: true,
@@ -1022,7 +852,6 @@ var Links390x = obj.LinkArch{
 	Arch:       sys.ArchS390X,
 	Preprocess: preprocess,
 	Assemble:   spanz,
-	Follow:     follow,
 	Progedit:   progedit,
 	UnaryDst:   unaryDst,
 }
diff --git a/src/cmd/internal/obj/x86/obj6.go b/src/cmd/internal/obj/x86/obj6.go
index f1e2b2507d..ec73bb3327 100644
--- a/src/cmd/internal/obj/x86/obj6.go
+++ b/src/cmd/internal/obj/x86/obj6.go
@@ -34,7 +34,6 @@ import (
 	"cmd/internal/obj"
 	"cmd/internal/sys"
 	"fmt"
-	"log"
 	"math"
 	"strings"
 )
@@ -1183,241 +1182,6 @@ func stacksplit(ctxt *obj.Link, p *obj.Prog, framesize int32, textarg int32) *ob
 	return jls
 }
 
-func follow(ctxt *obj.Link, s *obj.LSym) {
-	ctxt.Cursym = s
-
-	firstp := ctxt.NewProg()
-	lastp := firstp
-	xfol(ctxt, s.Text, &lastp)
-	lastp.Link = nil
-	s.Text = firstp.Link
-}
-
-func nofollow(a obj.As) bool {
-	switch a {
-	case obj.AJMP,
-		obj.ARET,
-		AIRETL,
-		AIRETQ,
-		AIRETW,
-		ARETFL,
-		ARETFQ,
-		ARETFW,
-		obj.AUNDEF:
-		return true
-	}
-
-	return false
-}
-
-func pushpop(a obj.As) bool {
-	switch a {
-	case APUSHL,
-		APUSHFL,
-		APUSHQ,
-		APUSHFQ,
-		APUSHW,
-		APUSHFW,
-		APOPL,
-		APOPFL,
-		APOPQ,
-		APOPFQ,
-		APOPW,
-		APOPFW:
-		return true
-	}
-
-	return false
-}
-
-func relinv(a obj.As) obj.As {
-	switch a {
-	case AJEQ:
-		return AJNE
-	case AJNE:
-		return AJEQ
-	case AJLE:
-		return AJGT
-	case AJLS:
-		return AJHI
-	case AJLT:
-		return AJGE
-	case AJMI:
-		return AJPL
-	case AJGE:
-		return AJLT
-	case AJPL:
-		return AJMI
-	case AJGT:
-		return AJLE
-	case AJHI:
-		return AJLS
-	case AJCS:
-		return AJCC
-	case AJCC:
-		return AJCS
-	case AJPS:
-		return AJPC
-	case AJPC:
-		return AJPS
-	case AJOS:
-		return AJOC
-	case AJOC:
-		return AJOS
-	}
-
-	log.Fatalf("unknown relation: %s", a)
-	return 0
-}
-
-func xfol(ctxt *obj.Link, p *obj.Prog, last **obj.Prog) {
-	var q *obj.Prog
-	var i int
-	var a obj.As
-
-loop:
-	if p == nil {
-		return
-	}
-	if p.As == obj.AJMP {
-		q = p.Pcond
-		if q != nil && q.As != obj.ATEXT {
-			/* mark instruction as done and continue layout at target of jump */
-			p.Mark |= DONE
-
-			p = q
-			if p.Mark&DONE == 0 {
-				goto loop
-			}
-		}
-	}
-
-	if p.Mark&DONE != 0 {
-		/*
-		 * p goes here, but already used it elsewhere.
-		 * copy up to 4 instructions or else branch to other copy.
-		 */
-		i = 0
-		q = p
-		for ; i < 4; i, q = i+1, q.Link {
-			if q == nil {
-				break
-			}
-			if q == *last {
-				break
-			}
-			a = q.As
-			if a == obj.ANOP {
-				i--
-				continue
-			}
-
-			if nofollow(a) || pushpop(a) {
-				break // NOTE(rsc): arm does goto copy
-			}
-			if q.Pcond == nil || q.Pcond.Mark&DONE != 0 {
-				continue
-			}
-			if a == obj.ACALL || a == ALOOP {
-				continue
-			}
-			for {
-				if p.As == obj.ANOP {
-					p = p.Link
-					continue
-				}
-
-				q = obj.Copyp(ctxt, p)
-				p = p.Link
-				q.Mark |= DONE
-				(*last).Link = q
-				*last = q
-				if q.As != a || q.Pcond == nil || q.Pcond.Mark&DONE != 0 {
-					continue
-				}
-
-				q.As = relinv(q.As)
-				p = q.Pcond
-				q.Pcond = q.Link
-				q.Link = p
-				xfol(ctxt, q.Link, last)
-				p = q.Link
-				if p.Mark&DONE != 0 {
-					return
-				}
-				goto loop
-				/* */
-			}
-		}
-		q = ctxt.NewProg()
-		q.As = obj.AJMP
-		q.Pos = p.Pos
-		q.To.Type = obj.TYPE_BRANCH
-		q.To.Offset = p.Pc
-		q.Pcond = p
-		p = q
-	}
-
-	/* emit p */
-	p.Mark |= DONE
-
-	(*last).Link = p
-	*last = p
-	a = p.As
-
-	/* continue loop with what comes after p */
-	if nofollow(a) {
-		return
-	}
-	if p.Pcond != nil && a != obj.ACALL {
-		/*
-		 * some kind of conditional branch.
-		 * recurse to follow one path.
-		 * continue loop on the other.
-		 */
-		q = obj.Brchain(ctxt, p.Pcond)
-		if q != nil {
-			p.Pcond = q
-		}
-		q = obj.Brchain(ctxt, p.Link)
-		if q != nil {
-			p.Link = q
-		}
-		if p.From.Type == obj.TYPE_CONST {
-			if p.From.Offset == 1 {
-				/*
-				 * expect conditional jump to be taken.
-				 * rewrite so that's the fall-through case.
-				 */
-				p.As = relinv(a)
-
-				q = p.Link
-				p.Link = p.Pcond
-				p.Pcond = q
-			}
-		} else {
-			q = p.Link
-			if q.Mark&DONE != 0 {
-				if a != ALOOP {
-					p.As = relinv(a)
-					p.Link = p.Pcond
-					p.Pcond = q
-				}
-			}
-		}
-
-		xfol(ctxt, p.Link, last)
-		if p.Pcond.Mark&DONE != 0 {
-			return
-		}
-		p = p.Pcond
-		goto loop
-	}
-
-	p = p.Link
-	goto loop
-}
-
 var unaryDst = map[obj.As]bool{
 	ABSWAPL:    true,
 	ABSWAPQ:    true,
@@ -1472,7 +1236,6 @@ var Linkamd64 = obj.LinkArch{
 	Arch:       sys.ArchAMD64,
 	Preprocess: preprocess,
 	Assemble:   span6,
-	Follow:     follow,
 	Progedit:   progedit,
 	UnaryDst:   unaryDst,
 }
@@ -1481,7 +1244,6 @@ var Linkamd64p32 = obj.LinkArch{
 	Arch:       sys.ArchAMD64P32,
 	Preprocess: preprocess,
 	Assemble:   span6,
-	Follow:     follow,
 	Progedit:   progedit,
 	UnaryDst:   unaryDst,
 }
@@ -1490,7 +1252,6 @@ var Link386 = obj.LinkArch{
 	Arch:       sys.Arch386,
 	Preprocess: preprocess,
 	Assemble:   span6,
-	Follow:     follow,
 	Progedit:   progedit,
 	UnaryDst:   unaryDst,
 }