[release-branch.go1.15] cmd/internal/obj: stop removing NOPs from instruction stream

This has already been done for s390x, ppc64. This CL is for
all the other architectures.

Fixes #40798

Change-Id: Idd1816e057df63022d47e99fa06617811d8c8489
Reviewed-on: https://go-review.googlesource.com/c/go/+/248684
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
(cherry picked from commit 46ca7b5ee2a8582736f1ddac27d8660e1104c345)
Reviewed-on: https://go-review.googlesource.com/c/go/+/249444
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>

6 files changed, 14 insertions, 123 deletions

diff --git a/src/cmd/internal/obj/arm/asm5.go b/src/cmd/internal/obj/arm/asm5.go
index f66f8aaf84..7b7e42ee2e 100644
--- a/src/cmd/internal/obj/arm/asm5.go
+++ b/src/cmd/internal/obj/arm/asm5.go
@@ -327,6 +327,9 @@ var optab = []Optab{
 	{obj.APCDATA, C_LCON, C_NONE, C_LCON, 0, 0, 0, 0, 0, 0},
 	{obj.AFUNCDATA, C_LCON, C_NONE, C_ADDR, 0, 0, 0, 0, 0, 0},
 	{obj.ANOP, C_NONE, C_NONE, C_NONE, 0, 0, 0, 0, 0, 0},
+	{obj.ANOP, C_LCON, C_NONE, C_NONE, 0, 0, 0, 0, 0, 0}, // nop variants, see #40689
+	{obj.ANOP, C_REG, C_NONE, C_NONE, 0, 0, 0, 0, 0, 0},
+	{obj.ANOP, C_FREG, C_NONE, C_NONE, 0, 0, 0, 0, 0, 0},
 	{obj.ADUFFZERO, C_NONE, C_NONE, C_SBRA, 5, 4, 0, 0, 0, 0}, // same as ABL
 	{obj.ADUFFCOPY, C_NONE, C_NONE, C_SBRA, 5, 4, 0, 0, 0, 0}, // same as ABL
 	{obj.AXXX, C_NONE, C_NONE, C_NONE, 0, 4, 0, 0, 0, 0},
diff --git a/src/cmd/internal/obj/arm/obj5.go b/src/cmd/internal/obj/arm/obj5.go
index 008118c47b..86831f2b44 100644
--- a/src/cmd/internal/obj/arm/obj5.go
+++ b/src/cmd/internal/obj/arm/obj5.go
@@ -276,67 +276,21 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 
 	/*
 	 * find leaf subroutines
-	 * strip NOPs
-	 * expand RET
-	 * expand BECOME pseudo
 	 */
-	var q1 *obj.Prog
-	var q *obj.Prog
 	for p := cursym.Func.Text; p != nil; p = p.Link {
 		switch p.As {
 		case obj.ATEXT:
 			p.Mark |= LEAF
 
-		case obj.ARET:
-			break
-
 		case ADIV, ADIVU, AMOD, AMODU:
-			q = p
 			cursym.Func.Text.Mark &^= LEAF
-			continue
-
-		case obj.ANOP:
-			q1 = p.Link
-			q.Link = q1 /* q is non-nop */
-			if q1 != nil {
-				q1.Mark |= p.Mark
-			}
-			continue
 
 		case ABL,
 			ABX,
 			obj.ADUFFZERO,
 			obj.ADUFFCOPY:
 			cursym.Func.Text.Mark &^= LEAF
-			fallthrough
-
-		case AB,
-			ABEQ,
-			ABNE,
-			ABCS,
-			ABHS,
-			ABCC,
-			ABLO,
-			ABMI,
-			ABPL,
-			ABVS,
-			ABVC,
-			ABHI,
-			ABLS,
-			ABGE,
-			ABLT,
-			ABGT,
-			ABLE:
-			q1 = p.Pcond
-			if q1 != nil {
-				for q1.As == obj.ANOP {
-					q1 = q1.Link
-					p.Pcond = q1
-				}
-			}
 		}
-
-		q = p
 	}
 
 	var q2 *obj.Prog
diff --git a/src/cmd/internal/obj/arm64/asm7.go b/src/cmd/internal/obj/arm64/asm7.go
index df17729a76..f18799b60a 100644
--- a/src/cmd/internal/obj/arm64/asm7.go
+++ b/src/cmd/internal/obj/arm64/asm7.go
@@ -837,6 +837,9 @@ var optab = []Optab{
 	{obj.APCDATA, C_VCON, C_NONE, C_NONE, C_VCON, 0, 0, 0, 0, 0},
 	{obj.AFUNCDATA, C_VCON, C_NONE, C_NONE, C_ADDR, 0, 0, 0, 0, 0},
 	{obj.ANOP, C_NONE, C_NONE, C_NONE, C_NONE, 0, 0, 0, 0, 0},
+	{obj.ANOP, C_LCON, C_NONE, C_NONE, C_NONE, 0, 0, 0, 0, 0}, // nop variants, see #40689
+	{obj.ANOP, C_REG, C_NONE, C_NONE, C_NONE, 0, 0, 0, 0, 0},
+	{obj.ANOP, C_VREG, C_NONE, C_NONE, C_NONE, 0, 0, 0, 0, 0},
 	{obj.ADUFFZERO, C_NONE, C_NONE, C_NONE, C_SBRA, 5, 4, 0, 0, 0}, // same as AB/ABL
 	{obj.ADUFFCOPY, C_NONE, C_NONE, C_NONE, C_SBRA, 5, 4, 0, 0, 0}, // same as AB/ABL
 	{obj.APCALIGN, C_LCON, C_NONE, C_NONE, C_NONE, 0, 0, 0, 0, 0},  // align code
diff --git a/src/cmd/internal/obj/arm64/obj7.go b/src/cmd/internal/obj/arm64/obj7.go
index b046685ada..0d74430053 100644
--- a/src/cmd/internal/obj/arm64/obj7.go
+++ b/src/cmd/internal/obj/arm64/obj7.go
@@ -468,73 +468,21 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 
 	/*
 	 * find leaf subroutines
-	 * strip NOPs
-	 * expand RET
 	 */
-	q := (*obj.Prog)(nil)
-	var q1 *obj.Prog
 	for p := c.cursym.Func.Text; p != nil; p = p.Link {
 		switch p.As {
 		case obj.ATEXT:
 			p.Mark |= LEAF
 
-		case obj.ARET:
-			break
-
-		case obj.ANOP:
-			if p.Link != nil {
-				q1 = p.Link
-				q.Link = q1 /* q is non-nop */
-				q1.Mark |= p.Mark
-			}
-			continue
-
 		case ABL,
 			obj.ADUFFZERO,
 			obj.ADUFFCOPY:
 			c.cursym.Func.Text.Mark &^= LEAF
-			fallthrough
-
-		case ACBNZ,
-			ACBZ,
-			ACBNZW,
-			ACBZW,
-			ATBZ,
-			ATBNZ,
-			AB,
-			ABEQ,
-			ABNE,
-			ABCS,
-			ABHS,
-			ABCC,
-			ABLO,
-			ABMI,
-			ABPL,
-			ABVS,
-			ABVC,
-			ABHI,
-			ABLS,
-			ABGE,
-			ABLT,
-			ABGT,
-			ABLE,
-			AADR, /* strange */
-			AADRP:
-			q1 = p.Pcond
-
-			if q1 != nil {
-				for q1.As == obj.ANOP {
-					q1 = q1.Link
-					p.Pcond = q1
-				}
-			}
-
-			break
 		}
-
-		q = p
 	}
 
+	var q *obj.Prog
+	var q1 *obj.Prog
 	var retjmp *obj.LSym
 	for p := c.cursym.Func.Text; p != nil; p = p.Link {
 		o := p.As
diff --git a/src/cmd/internal/obj/mips/asm0.go b/src/cmd/internal/obj/mips/asm0.go
index faa12bf133..faa827da9f 100644
--- a/src/cmd/internal/obj/mips/asm0.go
+++ b/src/cmd/internal/obj/mips/asm0.go
@@ -391,6 +391,9 @@ var optab = []Optab{
 	{obj.APCDATA, C_LCON, C_NONE, C_LCON, 0, 0, 0, 0, 0},
 	{obj.AFUNCDATA, C_SCON, C_NONE, C_ADDR, 0, 0, 0, 0, 0},
 	{obj.ANOP, C_NONE, C_NONE, C_NONE, 0, 0, 0, 0, 0},
+	{obj.ANOP, C_LCON, C_NONE, C_NONE, 0, 0, 0, 0, 0}, // nop variants, see #40689
+	{obj.ANOP, C_REG, C_NONE, C_NONE, 0, 0, 0, 0, 0},
+	{obj.ANOP, C_FREG, C_NONE, C_NONE, 0, 0, 0, 0, 0},
 	{obj.ADUFFZERO, C_NONE, C_NONE, C_LBRA, 11, 4, 0, 0, 0}, // same as AJMP
 	{obj.ADUFFCOPY, C_NONE, C_NONE, C_LBRA, 11, 4, 0, 0, 0}, // same as AJMP
 
diff --git a/src/cmd/internal/obj/mips/obj0.go b/src/cmd/internal/obj/mips/obj0.go
index 3106143844..77cad979a6 100644
--- a/src/cmd/internal/obj/mips/obj0.go
+++ b/src/cmd/internal/obj/mips/obj0.go
@@ -158,19 +158,14 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 
 	/*
 	 * find leaf subroutines
-	 * strip NOPs
 	 * expand RET
 	 * expand BECOME pseudo
 	 */
 
-	var q *obj.Prog
-	var q1 *obj.Prog
 	for p := c.cursym.Func.Text; p != nil; p = p.Link {
 		switch p.As {
 		/* too hard, just leave alone */
 		case obj.ATEXT:
-			q = p
-
 			p.Mark |= LABEL | LEAF | SYNC
 			if p.Link != nil {
 				p.Link.Mark |= LABEL
@@ -179,7 +174,6 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 		/* too hard, just leave alone */
 		case AMOVW,
 			AMOVV:
-			q = p
 			if p.To.Type == obj.TYPE_REG && p.To.Reg >= REG_SPECIAL {
 				p.Mark |= LABEL | SYNC
 				break
@@ -195,11 +189,9 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 			ATLBWI,
 			ATLBP,
 			ATLBR:
-			q = p
 			p.Mark |= LABEL | SYNC
 
 		case ANOR:
-			q = p
 			if p.To.Type == obj.TYPE_REG {
 				if p.To.Reg == REGZERO {
 					p.Mark |= LABEL | SYNC
@@ -235,8 +227,7 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 			} else {
 				p.Mark |= BRANCH
 			}
-			q = p
-			q1 = p.Pcond
+			q1 := p.Pcond
 			if q1 != nil {
 				for q1.As == obj.ANOP {
 					q1 = q1.Link
@@ -254,24 +245,11 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 			if q1 != nil {
 				q1.Mark |= LABEL
 			}
-			continue
 
 		case ARET:
-			q = p
 			if p.Link != nil {
 				p.Link.Mark |= LABEL
 			}
-			continue
-
-		case obj.ANOP:
-			q1 = p.Link
-			q.Link = q1 /* q is non-nop */
-			q1.Mark |= p.Mark
-			continue
-
-		default:
-			q = p
-			continue
 		}
 	}
 
@@ -284,6 +262,8 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym, newprog obj.ProgAlloc) {
 		mov = AMOVW
 	}
 
+	var q *obj.Prog
+	var q1 *obj.Prog
 	autosize := int32(0)
 	var p1 *obj.Prog
 	var p2 *obj.Prog