cmd/internal/obj/x86: accept TYPE_MEM in CMPPS 3rd argument

(Because that's what the assembly files actually say - no $ on the constant.)

Change-Id: Idb774cdca0e089c4ac24ab665e23290bf7b565bf
Reviewed-on: https://go-review.googlesource.com/6895Reviewed-by: Rob Pike <r@golang.org>

src/cmd/internal/obj/x86/obj6.go

@@ -186,6 +186,15 @@ func progedit(ctxt *obj.Link, p *obj.Prog) {
 		}
 	}
 
+	// Rewrite 0 to $0 in 3rd argment to CMPPS etc.
+	// That's what the tables expect.
+	switch p.As {
+	case ACMPPD, ACMPPS, ACMPSD, ACMPSS:
+		if p.To.Type == obj.TYPE_MEM && p.To.Name == obj.NAME_NONE && p.To.Reg == REG_NONE && p.To.Index == REG_NONE && p.To.Sym == nil {
+			p.To.Type = obj.TYPE_CONST
+		}
+	}
+
 	// Rewrite float constants to values stored in memory.
 	switch p.As {
 	// Convert AMOVSS $(0), Xx to AXORPS Xx, Xx

src/cmd/old6a/a.y

@@ -302,7 +302,8 @@ spec8:	/* CMPPS/CMPPD */
 	rem ',' reg ',' con
 	{
 		$$.from = $1;
-		$$.to = $3;
+		$$.from3 = $3;
+		$$.to.Type = obj.TYPE_MEM; // to give library something to do
 		$$.to.Offset = $5;
 	}