cmd/compile: grow stack before test() to avoid gdb misbehavior

While next-ing over a call in gdb, if execution of that call
causes a goroutine's stack to grow (i.e., be moved), gdb loses
track and runs ahead to the next breakpoint, or to the end of
the program, whichever comes first.

Prevent this by preemptively growing the stack so that
ssa/debug_test.go will reliably measure what is intended,
the goodness of line number placement and variable printing.

Fixes #25497.

Change-Id: I8daf931650292a8c8faad2285d7fd405f2157bd2
Reviewed-on: https://go-review.googlesource.com/114080
Run-TryBot: David Chase <drchase@google.com>
Reviewed-by: Austin Clements <austin@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/compile/internal/ssa/testdata/hist.dlv-dbg.nexts

@@ -96,4 +96,4 @@
 87:			if a == 0 { //gdb-opt=(a,n,t)
 88:				continue
 86:		for i, a := range hist {
-98:	}
+99:	}

src/cmd/compile/internal/ssa/testdata/hist.dlv-opt.nexts

@@ -148,4 +148,4 @@
 86:		for i, a := range hist {
 87:			if a == 0 { //gdb-opt=(a,n,t)
 86:		for i, a := range hist {
-98:	}
+99:	}

src/cmd/compile/internal/ssa/testdata/hist.gdb-dbg.nexts

@@ -120,4 +120,4 @@ t = 22
 87:			if a == 0 { //gdb-opt=(a,n,t)
 88:				continue
 86:		for i, a := range hist {
-98:	}
+99:	}

src/cmd/compile/internal/ssa/testdata/hist.gdb-opt.nexts

@@ -158,4 +158,4 @@ a = 0
 n = 9
 t = 22
 86:		for i, a := range hist {
-98:	}
+99:	}

src/cmd/compile/internal/ssa/testdata/hist.go

@@ -94,5 +94,13 @@ func test() {
 }
 
 func main() {
+	growstack() // Use stack early to prevent growth during test, which confuses gdb
 	test()
 }
+
+var snk string
+
+//go:noinline
+func growstack() {
+	snk = fmt.Sprintf("%#v,%#v,%#v", 1, true, "cat")
+}

src/cmd/compile/internal/ssa/testdata/i22558.dlv-dbg.nexts

@@ -8,4 +8,4 @@
 27:		for _, p := range t.stuff {
 28:			if isFoo(t, p) {
 29:				return
-43:	}
+44:	}

src/cmd/compile/internal/ssa/testdata/i22558.go

@@ -37,7 +37,15 @@ func isFoo(t *thing, b big) bool {
 }
 
 func main() {
+	growstack() // Use stack early to prevent growth during test, which confuses gdb
 	t := &thing{name: "t", self: nil, next: nil, stuff: make([]big, 1)}
 	u := thing{name: "u", self: t, next: t, stuff: make([]big, 1)}
 	test(t, &u)
 }
+
+var snk string
+
+//go:noinline
+func growstack() {
+	snk = fmt.Sprintf("%#v,%#v,%#v", 1, true, "cat")
+}

src/cmd/compile/internal/ssa/testdata/i22600.dlv-dbg-race.nexts

@@ -4,4 +4,4 @@
 10:		if err != nil {
 14:		fmt.Println(pwd)
 15:	}
-19:	}
+20:	}

src/cmd/compile/internal/ssa/testdata/i22600.gdb-dbg-race.nexts

@@ -4,4 +4,4 @@
 10:		if err != nil {
 14:		fmt.Println(pwd)
 15:	}
-19:	}
+20:	}

src/cmd/compile/internal/ssa/testdata/i22600.go

@@ -15,5 +15,13 @@ func test() {
 }
 
 func main() {
+	growstack() // Use stack early to prevent growth during test, which confuses gdb
 	test()
 }
+
+var snk string
+
+//go:noinline
+func growstack() {
+	snk = fmt.Sprintf("%#v,%#v,%#v", 1, true, "cat")
+}

src/cmd/compile/internal/ssa/testdata/scopes.dlv-dbg.nexts

   ./testdata/scopes.go
-21:	func test() {
-22:		x := id(0)
-23:		y := id(0)
-24:		fmt.Println(x)
-25:		for i := x; i < 3; i++ {
-26:			x := i * i
-27:			y += id(x) //gdb-dbg=(x,y)//gdb-opt=(x,y)
-25:		for i := x; i < 3; i++ {
-26:			x := i * i
-27:			y += id(x) //gdb-dbg=(x,y)//gdb-opt=(x,y)
-25:		for i := x; i < 3; i++ {
-26:			x := i * i
-27:			y += id(x) //gdb-dbg=(x,y)//gdb-opt=(x,y)
-25:		for i := x; i < 3; i++ {
-29:		y = x + y //gdb-dbg=(x,y)//gdb-opt=(x,y)
-30:		fmt.Println(x, y)
-32:		for x := 0; x <= 1; x++ { // From delve scopetest.go
-33:			a := y
-34:			f1(a)
-36:				b := 0
-37:				f2(b)
-38:				if gretbool() {
-39:					c := 0
-40:					f3(c)
-45:				f5(b)
-47:			f6(a)
-32:		for x := 0; x <= 1; x++ { // From delve scopetest.go
-33:			a := y
-34:			f1(a)
-36:				b := 0
-37:				f2(b)
-38:				if gretbool() {
-42:					c := 1.1
-43:					f4(int(c))
-45:				f5(b)
-47:			f6(a)
-32:		for x := 0; x <= 1; x++ { // From delve scopetest.go
-52:				j = id(1)
-53:				f = id(2)
-55:			for i := 0; i <= 5; i++ {
-56:				j += j * (j ^ 3) / 100
-57:				if i == f {
-61:				sleepytime()
-55:			for i := 0; i <= 5; i++ {
-56:				j += j * (j ^ 3) / 100
-57:				if i == f {
-61:				sleepytime()
-55:			for i := 0; i <= 5; i++ {
-56:				j += j * (j ^ 3) / 100
-57:				if i == f {
-58:					fmt.Println("foo")
-59:					break
-63:			helloworld()
-65:	}
-14:	}
+22:	func test() {
+23:		x := id(0)
+24:		y := id(0)
+25:		fmt.Println(x)
+26:		for i := x; i < 3; i++ {
+27:			x := i * i
+28:			y += id(x) //gdb-dbg=(x,y)//gdb-opt=(x,y)
+26:		for i := x; i < 3; i++ {
+27:			x := i * i
+28:			y += id(x) //gdb-dbg=(x,y)//gdb-opt=(x,y)
+26:		for i := x; i < 3; i++ {
+27:			x := i * i
+28:			y += id(x) //gdb-dbg=(x,y)//gdb-opt=(x,y)
+26:		for i := x; i < 3; i++ {
+30:		y = x + y //gdb-dbg=(x,y)//gdb-opt=(x,y)
+31:		fmt.Println(x, y)
+33:		for x := 0; x <= 1; x++ { // From delve scopetest.go
+34:			a := y
+35:			f1(a)
+37:				b := 0
+38:				f2(b)
+39:				if gretbool() {
+40:					c := 0
+41:					f3(c)
+46:				f5(b)
+48:			f6(a)
+33:		for x := 0; x <= 1; x++ { // From delve scopetest.go
+34:			a := y
+35:			f1(a)
+37:				b := 0
+38:				f2(b)
+39:				if gretbool() {
+43:					c := 1.1
+44:					f4(int(c))
+46:				f5(b)
+48:			f6(a)
+33:		for x := 0; x <= 1; x++ { // From delve scopetest.go
+53:				j = id(1)
+54:				f = id(2)
+56:			for i := 0; i <= 5; i++ {
+57:				j += j * (j ^ 3) / 100
+58:				if i == f {
+62:				sleepytime()
+56:			for i := 0; i <= 5; i++ {
+57:				j += j * (j ^ 3) / 100
+58:				if i == f {
+62:				sleepytime()
+56:			for i := 0; i <= 5; i++ {
+57:				j += j * (j ^ 3) / 100
+58:				if i == f {
+59:					fmt.Println("foo")
+60:					break
+64:			helloworld()
+66:	}
+15:	}

src/cmd/compile/internal/ssa/testdata/scopes.dlv-opt.nexts

   ./testdata/scopes.go
-21:	func test() {
-22:		x := id(0)
-23:		y := id(0)
-24:		fmt.Println(x)
-25:		for i := x; i < 3; i++ {
-29:		y = x + y //gdb-dbg=(x,y)//gdb-opt=(x,y)
-25:		for i := x; i < 3; i++ {
-29:		y = x + y //gdb-dbg=(x,y)//gdb-opt=(x,y)
-25:		for i := x; i < 3; i++ {
-26:			x := i * i
-27:			y += id(x) //gdb-dbg=(x,y)//gdb-opt=(x,y)
-25:		for i := x; i < 3; i++ {
-27:			y += id(x) //gdb-dbg=(x,y)//gdb-opt=(x,y)
-29:		y = x + y //gdb-dbg=(x,y)//gdb-opt=(x,y)
-25:		for i := x; i < 3; i++ {
-26:			x := i * i
-27:			y += id(x) //gdb-dbg=(x,y)//gdb-opt=(x,y)
-25:		for i := x; i < 3; i++ {
-27:			y += id(x) //gdb-dbg=(x,y)//gdb-opt=(x,y)
-29:		y = x + y //gdb-dbg=(x,y)//gdb-opt=(x,y)
-25:		for i := x; i < 3; i++ {
-26:			x := i * i
-27:			y += id(x) //gdb-dbg=(x,y)//gdb-opt=(x,y)
-25:		for i := x; i < 3; i++ {
-27:			y += id(x) //gdb-dbg=(x,y)//gdb-opt=(x,y)
-29:		y = x + y //gdb-dbg=(x,y)//gdb-opt=(x,y)
-25:		for i := x; i < 3; i++ {
-30:		fmt.Println(x, y)
-29:		y = x + y //gdb-dbg=(x,y)//gdb-opt=(x,y)
-30:		fmt.Println(x, y)
-21:	func test() {
-32:		for x := 0; x <= 1; x++ { // From delve scopetest.go
-34:			f1(a)
-37:				f2(b)
-38:				if gretbool() {
-40:					f3(c)
-45:				f5(b)
-47:			f6(a)
-32:		for x := 0; x <= 1; x++ { // From delve scopetest.go
-34:			f1(a)
-37:				f2(b)
-38:				if gretbool() {
-43:					f4(int(c))
-45:				f5(b)
-47:			f6(a)
-32:		for x := 0; x <= 1; x++ { // From delve scopetest.go
-52:				j = id(1)
-53:				f = id(2)
-55:			for i := 0; i <= 5; i++ {
-57:				if i == f {
-55:			for i := 0; i <= 5; i++ {
-61:				sleepytime()
-55:			for i := 0; i <= 5; i++ {
-57:				if i == f {
-55:			for i := 0; i <= 5; i++ {
-61:				sleepytime()
-55:			for i := 0; i <= 5; i++ {
-57:				if i == f {
-58:					fmt.Println("foo")
-63:			helloworld()
-65:	}
-14:	}
+22:	func test() {
+23:		x := id(0)
+24:		y := id(0)
+25:		fmt.Println(x)
+26:		for i := x; i < 3; i++ {
+30:		y = x + y //gdb-dbg=(x,y)//gdb-opt=(x,y)
+26:		for i := x; i < 3; i++ {
+30:		y = x + y //gdb-dbg=(x,y)//gdb-opt=(x,y)
+26:		for i := x; i < 3; i++ {
+27:			x := i * i
+28:			y += id(x) //gdb-dbg=(x,y)//gdb-opt=(x,y)
+26:		for i := x; i < 3; i++ {
+28:			y += id(x) //gdb-dbg=(x,y)//gdb-opt=(x,y)
+30:		y = x + y //gdb-dbg=(x,y)//gdb-opt=(x,y)
+26:		for i := x; i < 3; i++ {
+27:			x := i * i
+28:			y += id(x) //gdb-dbg=(x,y)//gdb-opt=(x,y)
+26:		for i := x; i < 3; i++ {
+28:			y += id(x) //gdb-dbg=(x,y)//gdb-opt=(x,y)
+30:		y = x + y //gdb-dbg=(x,y)//gdb-opt=(x,y)
+26:		for i := x; i < 3; i++ {
+27:			x := i * i
+28:			y += id(x) //gdb-dbg=(x,y)//gdb-opt=(x,y)
+26:		for i := x; i < 3; i++ {
+28:			y += id(x) //gdb-dbg=(x,y)//gdb-opt=(x,y)
+30:		y = x + y //gdb-dbg=(x,y)//gdb-opt=(x,y)
+26:		for i := x; i < 3; i++ {
+31:		fmt.Println(x, y)
+30:		y = x + y //gdb-dbg=(x,y)//gdb-opt=(x,y)
+31:		fmt.Println(x, y)
+22:	func test() {
+33:		for x := 0; x <= 1; x++ { // From delve scopetest.go
+35:			f1(a)
+38:				f2(b)
+39:				if gretbool() {
+41:					f3(c)
+46:				f5(b)
+48:			f6(a)
+33:		for x := 0; x <= 1; x++ { // From delve scopetest.go
+35:			f1(a)
+38:				f2(b)
+39:				if gretbool() {
+44:					f4(int(c))
+46:				f5(b)
+48:			f6(a)
+33:		for x := 0; x <= 1; x++ { // From delve scopetest.go
+53:				j = id(1)
+54:				f = id(2)
+56:			for i := 0; i <= 5; i++ {
+58:				if i == f {
+56:			for i := 0; i <= 5; i++ {
+62:				sleepytime()
+56:			for i := 0; i <= 5; i++ {
+58:				if i == f {
+56:			for i := 0; i <= 5; i++ {
+62:				sleepytime()
+56:			for i := 0; i <= 5; i++ {
+58:				if i == f {
+59:					fmt.Println("foo")
+64:			helloworld()
+66:	}
+15:	}

src/cmd/compile/internal/ssa/testdata/scopes.gdb-dbg.nexts

   src/cmd/compile/internal/ssa/testdata/scopes.go
-21:	func test() {
-22:		x := id(0)
-23:		y := id(0)
-24:		fmt.Println(x)
+22:	func test() {
+23:		x := id(0)
+24:		y := id(0)
+25:		fmt.Println(x)
 0:
-26:			x := i * i
-27:			y += id(x) //gdb-dbg=(x,y)//gdb-opt=(x,y)
+27:			x := i * i
+28:			y += id(x) //gdb-dbg=(x,y)//gdb-opt=(x,y)
 x = 0
 y = 0
-25:		for i := x; i < 3; i++ {
-26:			x := i * i
-27:			y += id(x) //gdb-dbg=(x,y)//gdb-opt=(x,y)
+26:		for i := x; i < 3; i++ {
+27:			x := i * i
+28:			y += id(x) //gdb-dbg=(x,y)//gdb-opt=(x,y)
 x = 1
 y = 0
-25:		for i := x; i < 3; i++ {
-26:			x := i * i
-27:			y += id(x) //gdb-dbg=(x,y)//gdb-opt=(x,y)
+26:		for i := x; i < 3; i++ {
+27:			x := i * i
+28:			y += id(x) //gdb-dbg=(x,y)//gdb-opt=(x,y)
 x = 4
 y = 1
-25:		for i := x; i < 3; i++ {
-29:		y = x + y //gdb-dbg=(x,y)//gdb-opt=(x,y)
+26:		for i := x; i < 3; i++ {
+30:		y = x + y //gdb-dbg=(x,y)//gdb-opt=(x,y)
 x = 0
 y = 5
-30:		fmt.Println(x, y)
+31:		fmt.Println(x, y)
 0: 5
-33:			a := y
-34:			f1(a)
-36:				b := 0
-37:				f2(b)
-38:				if gretbool() {
-39:					c := 0
-40:					f3(c)
-45:				f5(b)
-47:			f6(a)
-32:		for x := 0; x <= 1; x++ { // From delve scopetest.go
-33:			a := y
-34:			f1(a)
-36:				b := 0
-37:				f2(b)
-38:				if gretbool() {
-42:					c := 1.1
-43:					f4(int(c))
-45:				f5(b)
-47:			f6(a)
-32:		for x := 0; x <= 1; x++ { // From delve scopetest.go
-52:				j = id(1)
-53:				f = id(2)
-55:			for i := 0; i <= 5; i++ {
-56:				j += j * (j ^ 3) / 100
-57:				if i == f {
-61:				sleepytime()
-55:			for i := 0; i <= 5; i++ {
-56:				j += j * (j ^ 3) / 100
-57:				if i == f {
-61:				sleepytime()
-55:			for i := 0; i <= 5; i++ {
-56:				j += j * (j ^ 3) / 100
-57:				if i == f {
-58:					fmt.Println("foo")
-59:					break
-63:			helloworld()
-65:	}
-14:	}
+34:			a := y
+35:			f1(a)
+37:				b := 0
+38:				f2(b)
+39:				if gretbool() {
+40:					c := 0
+41:					f3(c)
+46:				f5(b)
+48:			f6(a)
+33:		for x := 0; x <= 1; x++ { // From delve scopetest.go
+34:			a := y
+35:			f1(a)
+37:				b := 0
+38:				f2(b)
+39:				if gretbool() {
+43:					c := 1.1
+44:					f4(int(c))
+46:				f5(b)
+48:			f6(a)
+33:		for x := 0; x <= 1; x++ { // From delve scopetest.go
+53:				j = id(1)
+54:				f = id(2)
+56:			for i := 0; i <= 5; i++ {
+57:				j += j * (j ^ 3) / 100
+58:				if i == f {
+62:				sleepytime()
+56:			for i := 0; i <= 5; i++ {
+57:				j += j * (j ^ 3) / 100
+58:				if i == f {
+62:				sleepytime()
+56:			for i := 0; i <= 5; i++ {
+57:				j += j * (j ^ 3) / 100
+58:				if i == f {
+59:					fmt.Println("foo")
+60:					break
+64:			helloworld()
+66:	}
+15:	}

src/cmd/compile/internal/ssa/testdata/scopes.gdb-opt.nexts

   src/cmd/compile/internal/ssa/testdata/scopes.go
-21:	func test() {
-22:		x := id(0)
-23:		y := id(0)
-24:		fmt.Println(x)
+22:	func test() {
+23:		x := id(0)
+24:		y := id(0)
+25:		fmt.Println(x)
 0:
-26:			x := i * i
-27:			y += id(x) //gdb-dbg=(x,y)//gdb-opt=(x,y)
+27:			x := i * i
+28:			y += id(x) //gdb-dbg=(x,y)//gdb-opt=(x,y)
 x = 0
 y = 0
-25:		for i := x; i < 3; i++ {
-26:			x := i * i
-27:			y += id(x) //gdb-dbg=(x,y)//gdb-opt=(x,y)
+26:		for i := x; i < 3; i++ {
+27:			x := i * i
+28:			y += id(x) //gdb-dbg=(x,y)//gdb-opt=(x,y)
 x = 1
 y = 0
-25:		for i := x; i < 3; i++ {
-26:			x := i * i
-27:			y += id(x) //gdb-dbg=(x,y)//gdb-opt=(x,y)
+26:		for i := x; i < 3; i++ {
+27:			x := i * i
+28:			y += id(x) //gdb-dbg=(x,y)//gdb-opt=(x,y)
 x = 4
 y = 1
-25:		for i := x; i < 3; i++ {
-30:		fmt.Println(x, y)
-29:		y = x + y //gdb-dbg=(x,y)//gdb-opt=(x,y)
+26:		for i := x; i < 3; i++ {
+31:		fmt.Println(x, y)
+30:		y = x + y //gdb-dbg=(x,y)//gdb-opt=(x,y)
 x = 0
 y = 5
 0: 5
-34:			f1(a)
-37:				f2(b)
-38:				if gretbool() {
-40:					f3(c)
-45:				f5(b)
-47:			f6(a)
-32:		for x := 0; x <= 1; x++ { // From delve scopetest.go
-34:			f1(a)
-37:				f2(b)
-38:				if gretbool() {
-43:					f4(int(c))
-45:				f5(b)
-47:			f6(a)
-32:		for x := 0; x <= 1; x++ { // From delve scopetest.go
-52:				j = id(1)
-53:				f = id(2)
-55:			for i := 0; i <= 5; i++ {
-57:				if i == f {
-61:				sleepytime()
-55:			for i := 0; i <= 5; i++ {
-57:				if i == f {
-61:				sleepytime()
-55:			for i := 0; i <= 5; i++ {
-57:				if i == f {
-58:					fmt.Println("foo")
-63:			helloworld()
-65:	}
-14:	}
+35:			f1(a)
+38:				f2(b)
+39:				if gretbool() {
+41:					f3(c)
+46:				f5(b)
+48:			f6(a)
+33:		for x := 0; x <= 1; x++ { // From delve scopetest.go
+35:			f1(a)
+38:				f2(b)
+39:				if gretbool() {
+44:					f4(int(c))
+46:				f5(b)
+48:			f6(a)
+33:		for x := 0; x <= 1; x++ { // From delve scopetest.go
+53:				j = id(1)
+54:				f = id(2)
+56:			for i := 0; i <= 5; i++ {
+58:				if i == f {
+62:				sleepytime()
+56:			for i := 0; i <= 5; i++ {
+58:				if i == f {
+62:				sleepytime()
+56:			for i := 0; i <= 5; i++ {
+58:				if i == f {
+59:					fmt.Println("foo")
+64:			helloworld()
+66:	}
+15:	}

src/cmd/compile/internal/ssa/testdata/scopes.go

@@ -10,6 +10,7 @@ import (
 )
 
 func main() {
+	growstack() // Use stack early to prevent growth during test, which confuses gdb
 	test()
 }
 
@@ -97,3 +98,10 @@ func gretbool() bool {
 	boolvar = !boolvar
 	return x
 }
+
+var sink string
+
+//go:noinline
+func growstack() {
+	sink = fmt.Sprintf("%#v,%#v,%#v", 1, true, "cat")
+}