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cmd/internal/obj/x86: clean up byteswapreg

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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>
This commit is contained in:
Dave Cheney 2017-03-27 15:27:44 +11:00
parent b72636cbde
commit 54af18708b
1 changed files with 20 additions and 35 deletions
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55
src/cmd/internal/obj/x86/asm6.go
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@ -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 {