cmd/compile: combine similar code in amd64's assembly generator

BSFQ/BSRQ/BSFL/BSRL/SQRTSD have similar logic in amd64's assembly
generator. This CL combines them together while does not impact
generated amd64 code. The total size of
pkg/linux_amd64/cmd/compile/internal decreases about 1.8KB.

Change-Id: I5f3210c5178c20ac9108877c69f17234baf5b6b7
Reviewed-on: https://go-review.googlesource.com/c/140438
Run-TryBot: Ben Shi <powerman1st@163.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>

src/cmd/compile/internal/amd64/ssa.go

@@ -782,14 +782,14 @@ func ssaGenValue(s *gc.SSAGenState, v *ssa.Value) {
 		// Break false dependency on destination register.
 		opregreg(s, x86.AXORPS, r, r)
 		opregreg(s, v.Op.Asm(), r, v.Args[0].Reg())
+	case ssa.OpAMD64MOVQi2f, ssa.OpAMD64MOVQf2i, ssa.OpAMD64MOVLi2f, ssa.OpAMD64MOVLf2i:
+		var p *obj.Prog
+		switch v.Op {
 		case ssa.OpAMD64MOVQi2f, ssa.OpAMD64MOVQf2i:
-		p := s.Prog(x86.AMOVQ)
-		p.From.Type = obj.TYPE_REG
-		p.From.Reg = v.Args[0].Reg()
-		p.To.Type = obj.TYPE_REG
-		p.To.Reg = v.Reg()
+			p = s.Prog(x86.AMOVQ)
 		case ssa.OpAMD64MOVLi2f, ssa.OpAMD64MOVLf2i:
-		p := s.Prog(x86.AMOVL)
+			p = s.Prog(x86.AMOVL)
+		}
 		p.From.Type = obj.TYPE_REG
 		p.From.Reg = v.Args[0].Reg()
 		p.To.Type = obj.TYPE_REG
@@ -934,24 +934,17 @@ func ssaGenValue(s *gc.SSAGenState, v *ssa.Value) {
 		p := s.Prog(v.Op.Asm())
 		p.To.Type = obj.TYPE_REG
 		p.To.Reg = r
-	case ssa.OpAMD64BSFQ, ssa.OpAMD64BSRQ:
+	case ssa.OpAMD64BSFQ, ssa.OpAMD64BSRQ, ssa.OpAMD64BSFL, ssa.OpAMD64BSRL, ssa.OpAMD64SQRTSD:
 		p := s.Prog(v.Op.Asm())
 		p.From.Type = obj.TYPE_REG
 		p.From.Reg = v.Args[0].Reg()
 		p.To.Type = obj.TYPE_REG
+		switch v.Op {
+		case ssa.OpAMD64BSFQ, ssa.OpAMD64BSRQ:
 			p.To.Reg = v.Reg0()
-	case ssa.OpAMD64BSFL, ssa.OpAMD64BSRL:
-		p := s.Prog(v.Op.Asm())
-		p.From.Type = obj.TYPE_REG
-		p.From.Reg = v.Args[0].Reg()
-		p.To.Type = obj.TYPE_REG
-		p.To.Reg = v.Reg()
-	case ssa.OpAMD64SQRTSD:
-		p := s.Prog(v.Op.Asm())
-		p.From.Type = obj.TYPE_REG
-		p.From.Reg = v.Args[0].Reg()
-		p.To.Type = obj.TYPE_REG
+		case ssa.OpAMD64BSFL, ssa.OpAMD64BSRL, ssa.OpAMD64SQRTSD:
 			p.To.Reg = v.Reg()
+		}
 	case ssa.OpAMD64ROUNDSD:
 		p := s.Prog(v.Op.Asm())
 		val := v.AuxInt