cmd/internal/obj: delete Debugzerostack dead code

Fixes #11060

Change-Id: I4c6647fc2f103015b67e30dc2cdb6f771526c139
Reviewed-on: https://go-review.googlesource.com/13840Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/internal/obj/arm/obj5.go

@@ -186,65 +186,6 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym) {
 	cursym.Locals = autoffset
 	cursym.Args = p.To.Val.(int32)
 
-	if ctxt.Debugzerostack != 0 {
-		if autoffset != 0 && p.From3.Offset&obj.NOSPLIT == 0 {
-			// MOVW $4(R13), R1
-			p = obj.Appendp(ctxt, p)
-
-			p.As = AMOVW
-			p.From.Type = obj.TYPE_ADDR
-			p.From.Reg = REG_R13
-			p.From.Offset = 4
-			p.To.Type = obj.TYPE_REG
-			p.To.Reg = REG_R1
-
-			// MOVW $n(R13), R2
-			p = obj.Appendp(ctxt, p)
-
-			p.As = AMOVW
-			p.From.Type = obj.TYPE_ADDR
-			p.From.Reg = REG_R13
-			p.From.Offset = 4 + int64(autoffset)
-			p.To.Type = obj.TYPE_REG
-			p.To.Reg = REG_R2
-
-			// MOVW $0, R3
-			p = obj.Appendp(ctxt, p)
-
-			p.As = AMOVW
-			p.From.Type = obj.TYPE_CONST
-			p.From.Offset = 0
-			p.To.Type = obj.TYPE_REG
-			p.To.Reg = REG_R3
-
-			// L:
-			//	MOVW.nil R3, 0(R1) +4
-			//	CMP R1, R2
-			//	BNE L
-			pl := obj.Appendp(ctxt, p)
-			p := pl
-
-			p.As = AMOVW
-			p.From.Type = obj.TYPE_REG
-			p.From.Reg = REG_R3
-			p.To.Type = obj.TYPE_MEM
-			p.To.Reg = REG_R1
-			p.To.Offset = 4
-			p.Scond |= C_PBIT
-
-			p = obj.Appendp(ctxt, p)
-			p.As = ACMP
-			p.From.Type = obj.TYPE_REG
-			p.From.Reg = REG_R1
-			p.Reg = REG_R2
-
-			p = obj.Appendp(ctxt, p)
-			p.As = ABNE
-			p.To.Type = obj.TYPE_BRANCH
-			p.Pcond = pl
-		}
-	}
-
 	/*
 	 * find leaf subroutines
 	 * strip NOPs

src/cmd/internal/obj/link.go

@@ -466,7 +466,6 @@ type Link struct {
 	Arch               *LinkArch
 	Debugasm           int32
 	Debugvlog          int32
-	Debugzerostack     int32
 	Debugdivmod        int32
 	Debugpcln          int32
 	Flag_shared        int32

src/cmd/internal/obj/x86/obj6.go

@@ -657,51 +657,6 @@ func preprocess(ctxt *obj.Link, cursym *obj.LSym) {
 		p2.Pcond = p
 	}
 
-	if ctxt.Debugzerostack != 0 && autoffset != 0 && cursym.Text.From3.Offset&obj.NOSPLIT == 0 {
-		// 6l -Z means zero the stack frame on entry.
-		// This slows down function calls but can help avoid
-		// false positives in garbage collection.
-		p = obj.Appendp(ctxt, p)
-
-		p.As = AMOVQ
-		p.From.Type = obj.TYPE_REG
-		p.From.Reg = REG_SP
-		p.To.Type = obj.TYPE_REG
-		p.To.Reg = REG_DI
-		if p.Mode == 32 {
-			p.As = AMOVL
-		}
-
-		p = obj.Appendp(ctxt, p)
-		p.As = AMOVQ
-		p.From.Type = obj.TYPE_CONST
-		p.From.Offset = int64(autoffset) / int64(ctxt.Arch.Regsize)
-		p.To.Type = obj.TYPE_REG
-		p.To.Reg = REG_CX
-		if p.Mode == 32 {
-			p.As = AMOVL
-		}
-
-		p = obj.Appendp(ctxt, p)
-		p.As = AMOVQ
-		p.From.Type = obj.TYPE_CONST
-		p.From.Offset = 0
-		p.To.Type = obj.TYPE_REG
-		p.To.Reg = REG_AX
-		if p.Mode == 32 {
-			p.As = AMOVL
-		}
-
-		p = obj.Appendp(ctxt, p)
-		p.As = AREP
-
-		p = obj.Appendp(ctxt, p)
-		p.As = ASTOSQ
-		if p.Mode == 32 {
-			p.As = ASTOSL
-		}
-	}
-
 	var a int
 	var pcsize int
 	for ; p != nil; p = p.Link {