cmd/gc: factor newly-portable code into gc directory

This isn't everything, but it's a start.
Still producing bit-identical compiler output.

The semantics of the old back ends is preserved,
even when they are probably buggy.
There are some TODOs in gc/gsubr.c to
remove special cases to preserve bugs in 5g and 8g.

Change-Id: I28ae295fbfc94ef9df43e13ab96bd6fc2f194bc4
Reviewed-on: https://go-review.googlesource.com/3802
Reviewed-by: Austin Clements <austin@google.com>

4 files changed, 23 insertions, 29 deletions

diff --git a/src/liblink/asm5.c b/src/liblink/asm5.c
index 3947a571e5..398b7841c2 100644
--- a/src/liblink/asm5.c
+++ b/src/liblink/asm5.c
@@ -96,6 +96,7 @@ static Optab	optab[] =
 	{ ABL,		C_NONE,	C_NONE,	C_SBRA,		 5, 4, 0 },
 	{ ABX,		C_NONE,	C_NONE,	C_SBRA,		 74, 20, 0 },
 	{ ABEQ,		C_NONE,	C_NONE,	C_SBRA,		 5, 4, 0 },
+	{ ABEQ,		C_RCON,	C_NONE,	C_SBRA,		 5, 4, 0 }, // prediction hinted form, hint ignored
 
 	{ AB,		C_NONE,	C_NONE,	C_ROREG,	 6, 4, 0,	LPOOL },
 	{ ABL,		C_NONE,	C_NONE,	C_ROREG,	 7, 4, 0 },
@@ -353,14 +354,6 @@ static	uchar	xcmp[C_GOK+1][C_GOK+1];
 
 static LSym *deferreturn;
 
-static void
-nocache(Prog *p)
-{
-	p->optab = 0;
-	p->from.class = 0;
-	p->to.class = 0;
-}
-
 /* size of a case statement including jump table */
 static int32
 casesz(Link *ctxt, Prog *p)
diff --git a/src/liblink/go.c b/src/liblink/go.c
index 754a7cc15e..08ce82b30c 100644
--- a/src/liblink/go.c
+++ b/src/liblink/go.c
@@ -133,3 +133,24 @@ double2ieee(uint64 *ieee, float64 f)
 {
 	memmove(ieee, &f, 8);
 }
+
+void
+nopout(Prog *p)
+{
+	p->as = ANOP;
+	p->scond = zprog.scond;
+	p->from = zprog.from;
+	p->from3 = zprog.from3;
+	p->reg = zprog.reg;
+	p->to = zprog.to;
+}
+
+void
+nocache(Prog *p)
+{
+	p->optab = 0;
+	p->from.class = 0;
+	p->from3.class = 0;
+	p->to.class = 0;
+}
+
diff --git a/src/liblink/obj5.c b/src/liblink/obj5.c
index 805d7a59c2..abddbc3c4f 100644
--- a/src/liblink/obj5.c
+++ b/src/liblink/obj5.c
@@ -185,14 +185,6 @@ linkcase(Prog *casep)
 }
 
 static void
-nocache5(Prog *p)
-{
-	p->optab = 0;
-	p->from.class = 0;
-	p->to.class = 0;
-}
-
-static void
 preprocess(Link *ctxt, LSym *cursym)
 {
 	Prog *p, *pl, *p1, *p2, *q, *q1, *q2;
@@ -478,7 +470,7 @@ preprocess(Link *ctxt, LSym *cursym)
 			break;
 
 		case ARET:
-			nocache5(p);
+			nocache(p);
 			if(cursym->text->mark & LEAF) {
 				if(!autosize) {
 					p->as = AB;
diff --git a/src/liblink/obj6.c b/src/liblink/obj6.c
index cddc723bf2..546c89d53c 100644
--- a/src/liblink/obj6.c
+++ b/src/liblink/obj6.c
@@ -35,18 +35,6 @@
 #include "../cmd/6l/6.out.h"
 #include "../runtime/stack.h"
 
-static void
-nopout(Prog *p)
-{
-	p->as = ANOP;
-	p->from.type = TYPE_NONE;
-	p->from.reg = 0;
-	p->from.name = 0;
-	p->to.type = TYPE_NONE;
-	p->to.reg = 0;
-	p->to.name = 0;
-}
-
 static void nacladdr(Link*, Prog*, Addr*);
 
 static int