1 files changed, 28 insertions, 5 deletions

diff --git a/src/cmd/internal/obj/x86/asm6.go b/src/cmd/internal/obj/x86/asm6.go
index 115350637f..9ab6615e43 100644
--- a/src/cmd/internal/obj/x86/asm6.go
+++ b/src/cmd/internal/obj/x86/asm6.go
@@ -1895,7 +1895,7 @@ func span6(ctxt *obj.Link, s *obj.LSym) {
 
 			// process forward jumps to p
 			for q = p.Rel; q != nil; q = q.Forwd {
-				v = int32(p.Pc - (q.Pc + int64(q.Mark)))
+				v = int32(p.Pc - (q.Pc + int64(q.Isize)))
 				if q.Back&2 != 0 { // short
 					if v > 127 {
 						loop++
@@ -1908,7 +1908,7 @@ func span6(ctxt *obj.Link, s *obj.LSym) {
 						s.P[q.Pc+1] = byte(v)
 					}
 				} else {
-					bp = s.P[q.Pc+int64(q.Mark)-4:]
+					bp = s.P[q.Pc+int64(q.Isize)-4:]
 					bp[0] = byte(v)
 					bp = bp[1:]
 					bp[0] = byte(v >> 8)
@@ -1931,7 +1931,6 @@ func span6(ctxt *obj.Link, s *obj.LSym) {
 
 			obj.Symgrow(ctxt, s, p.Pc+int64(m))
 			copy(s.P[p.Pc:][:m], ctxt.And[:m])
-			p.Mark = uint16(m)
 			c += int32(m)
 		}
 
@@ -2272,8 +2271,28 @@ func oclass(ctxt *obj.Link, p *obj.Prog, a *obj.Addr) int {
 		return Yxxx
 
 	case obj.TYPE_MEM:
-		if a.Name != obj.NAME_NONE {
-			if ctxt.Asmode == 64 && (a.Reg != REG_NONE || a.Index != REG_NONE || a.Scale != 0) {
+		if a.Index == REG_SP {
+			// Can't use SP as the index register
+			return Yxxx
+		}
+		if ctxt.Asmode == 64 {
+			switch a.Name {
+			case obj.NAME_EXTERN, obj.NAME_STATIC, obj.NAME_GOTREF:
+				// Global variables can't use index registers and their
+				// base register is %rip (%rip is encoded as REG_NONE).
+				if a.Reg != REG_NONE || a.Index != REG_NONE || a.Scale != 0 {
+					return Yxxx
+				}
+			case obj.NAME_AUTO, obj.NAME_PARAM:
+				// These names must have a base of SP.  The old compiler
+				// uses 0 for the base register.  SSA uses REG_SP.
+				if a.Reg != REG_SP && a.Reg != 0 {
+					return Yxxx
+				}
+			case obj.NAME_NONE:
+				// everything is ok
+			default:
+				// unknown name
 				return Yxxx
 			}
 		}
@@ -2321,6 +2340,10 @@ func oclass(ctxt *obj.Link, p *obj.Prog, a *obj.Addr) int {
 			v = int64(int32(v))
 		}
 		if v == 0 {
+			if p.Mark&PRESERVEFLAGS != 0 {
+				// If PRESERVEFLAGS is set, avoid MOV $0, AX turning into XOR AX, AX.
+				return Yu7
+			}
 			return Yi0
 		}
 		if v == 1 {