cmd/internal/obj/x86: clean up byteswapreg

Make byteswapreg more Go like.

Change-Id: Ibdf3603cae9cad2b3465b4c224a28a4c4c745c2e
Reviewed-on: https://go-review.googlesource.com/38615
Run-TryBot: Dave Cheney <dave@cheney.net>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

diff --git a/src/cmd/internal/obj/x86/asm6.go b/src/cmd/internal/obj/x86/asm6.go
index fff17e5b75f47b6516263c5e72d44824339c71b7..86dfb28ad03db1ac3a32b9aef4386b8d6fc97cd0 100644 (file)
--- a/src/cmd/internal/obj/x86/asm6.go
+++ b/src/cmd/internal/obj/x86/asm6.go
@@ -4317,68 +4317,53 @@ bad:
 // If a is empty, it returns BX to account for MULB-like instructions
 // that might use DX and AX.
 func byteswapreg(ctxt *obj.Link, a *obj.Addr) int {
-       cand := 1
-       canc := cand
-       canb := canc
-       cana := canb
-
+       cana, canb, canc, cand := true, true, true, true
        if a.Type == obj.TYPE_NONE {
-               cand = 0
-               cana = cand
+               cana, cand = false, false
        }
 
        if a.Type == obj.TYPE_REG || ((a.Type == obj.TYPE_MEM || a.Type == obj.TYPE_ADDR) && a.Name == obj.NAME_NONE) {
                switch a.Reg {
                case REG_NONE:
-                       cand = 0
-                       cana = cand
-
+                       cana, cand = false, false
                case REG_AX, REG_AL, REG_AH:
-                       cana = 0
-
+                       cana = false
                case REG_BX, REG_BL, REG_BH:
-                       canb = 0
-
+                       canb = false
                case REG_CX, REG_CL, REG_CH:
-                       canc = 0
-
+                       canc = false
                case REG_DX, REG_DL, REG_DH:
-                       cand = 0
+                       cand = false
                }
        }
 
        if a.Type == obj.TYPE_MEM || a.Type == obj.TYPE_ADDR {
                switch a.Index {
                case REG_AX:
-                       cana = 0
-
+                       cana = false
                case REG_BX:
-                       canb = 0
-
+                       canb = false
                case REG_CX:
-                       canc = 0
-
+                       canc = false
                case REG_DX:
-                       cand = 0
+                       cand = false
                }
        }
 
-       if cana != 0 {
+       switch {
+       case cana:
                return REG_AX
-       }
-       if canb != 0 {
+       case canb:
                return REG_BX
-       }
-       if canc != 0 {
+       case canc:
                return REG_CX
-       }
-       if cand != 0 {
+       case cand:
                return REG_DX
+       default:
+               ctxt.Diag("impossible byte register")
+               log.Fatalf("bad code")
+               return 0
        }
-
-       ctxt.Diag("impossible byte register")
-       log.Fatalf("bad code")
-       return 0
 }
 
 func isbadbyte(a *obj.Addr) bool {