cmd/internal/obj/x86: add named consts for Prog.Back flags

Passes toolstash-check.

Change-Id: I7232ba43895a54b03cc328bb2e99c05c44eb6e8e
Reviewed-on: https://go-review.googlesource.com/107057
Reviewed-by: Ilya Tocar <ilya.tocar@intel.com>
Run-TryBot: Iskander Sharipov <iskander.sharipov@intel.com>

diff --git a/src/cmd/internal/obj/x86/asm6.go b/src/cmd/internal/obj/x86/asm6.go
index 72c6ca54d7d79a4a7afa22d473e33a1e4f61b428..ebf6209dbc8354c2688d5429694e6306ff7ad658 100644 (file)
--- a/src/cmd/internal/obj/x86/asm6.go
+++ b/src/cmd/internal/obj/x86/asm6.go
@@ -65,6 +65,19 @@ const (
        maxLoopPad = 0
 )
 
+// Bit flags that are used to express jump target properties.
+const (
+       // branchBackwards marks targets that are located behind.
+       // Used to express jumps to loop headers.
+       branchBackwards = (1 << iota)
+       // branchShort marks branches those target is close,
+       // with offset is in -128..127 range.
+       branchShort
+       // branchLoopHead marks loop entry.
+       // Used to insert padding for misaligned loops.
+       branchLoopHead
+)
+
 type Optab struct {
        as     obj.As
        ytab   []ytab
@@ -2125,11 +2138,11 @@ func span6(ctxt *obj.Link, s *obj.LSym, newprog obj.ProgAlloc) {
        var count int64 // rough count of number of instructions
        for p := s.Func.Text; p != nil; p = p.Link {
                count++
-               p.Back = 2 // use short branches first time through
+               p.Back = branchShort // use short branches first time through
                q = p.Pcond
-               if q != nil && (q.Back&2 != 0) {
-                       p.Back |= 1 // backward jump
-                       q.Back |= 4 // loop head
+               if q != nil && (q.Back&branchShort != 0) {
+                       p.Back |= branchBackwards
+                       q.Back |= branchLoopHead
                }
 
                if p.As == AADJSP {
@@ -2197,7 +2210,7 @@ func span6(ctxt *obj.Link, s *obj.LSym, newprog obj.ProgAlloc) {
                                }
                        }
 
-                       if (p.Back&4 != 0) && c&(loopAlign-1) != 0 {
+                       if (p.Back&branchLoopHead != 0) && c&(loopAlign-1) != 0 {
                                // pad with NOPs
                                v := -c & (loopAlign - 1)
 
@@ -2213,10 +2226,10 @@ func span6(ctxt *obj.Link, s *obj.LSym, newprog obj.ProgAlloc) {
                        // process forward jumps to p
                        for q = p.Rel; q != nil; q = q.Forwd {
                                v := int32(p.Pc - (q.Pc + int64(q.Isize)))
-                               if q.Back&2 != 0 { // short
+                               if q.Back&branchShort != 0 {
                                        if v > 127 {
                                                loop++
-                                               q.Back ^= 2
+                                               q.Back ^= branchShort
                                        }
 
                                        if q.As == AJCXZL || q.As == AXBEGIN {
@@ -4328,7 +4341,7 @@ func (ab *AsmBuf) doasm(ctxt *obj.Link, cursym *obj.LSym, p *obj.Prog) {
                                        log.Fatalf("bad code")
                                }
 
-                               if p.Back&1 != 0 {
+                               if p.Back&branchBackwards != 0 {
                                        v = q.Pc - (p.Pc + 2)
                                        if v >= -128 && p.As != AXBEGIN {
                                                if p.As == AJCXZL {
@@ -4358,7 +4371,7 @@ func (ab *AsmBuf) doasm(ctxt *obj.Link, cursym *obj.LSym, p *obj.Prog) {
                                p.Forwd = q.Rel
 
                                q.Rel = p
-                               if p.Back&2 != 0 && p.As != AXBEGIN { // short
+                               if p.Back&branchShort != 0 && p.As != AXBEGIN {
                                        if p.As == AJCXZL {
                                                ab.Put1(0x67)
                                        }