6g: simplify trampoline by postponing load.

	TEXT tramp
		MOVQ 8(SP), AX
		ADDQ $40, AX
		MOVQ AX, 8(SP)
		JMP oldfunc

	is now

	TEXT tramp
		ADDQ $40, 8(SP)
		JMP oldfunc

	and if s/40/0/, then it simplifies to

	TEXT tramp
		JMP oldfunc

	(the tramp is still needed to satisfy
	symbol references from other object files)

R=ken
OCL=28377
CL=28381

diff --git a/src/cmd/6g/obj.c b/src/cmd/6g/obj.c
index bdbf5c7671238761727c03af36e2d556d2f57795..1970d1fabcbec244ef95d18b0bc8a7069e2df374 100644 (file)
--- a/src/cmd/6g/obj.c
+++ b/src/cmd/6g/obj.c
@@ -272,7 +272,7 @@ data(void)
 {
        gflag = debug['g'];
        debug['g'] = 0;
-       
+
        if(estrdat == nil) {
                strdat = mal(sizeof(*pc));
                clearp(strdat);
@@ -324,7 +324,7 @@ datastring(char *s, int len, Addr *a)
                Strlit lit;
                char buf[100];
        } tmp;
-       
+
        // string
        memset(&ao, 0, sizeof(ao));
        ao.type = D_STATIC;
@@ -421,7 +421,7 @@ datagostring(Strlit *sval, Addr *a)
 
        wi = types[TUINT32]->width;
        wp = types[tptr]->width;
-       
+
        if(ap.index == D_STATIC) {
                // huge strings are made static to avoid long names
                snprint(namebuf, sizeof(namebuf), ".gostring.%d", ++gen);
@@ -457,7 +457,7 @@ datagostring(Strlit *sval, Addr *a)
        p->from.scale = wi;
        p->to = ac;
        p->to.offset = sval->len;
-       
+
        p = pc;
        ggloblsym(ao.sym, types[TSTRING]->width, ao.type == D_EXTERN);
        if(ao.type == D_STATIC)
@@ -553,7 +553,7 @@ void
 genembedtramp(Type *t, Sig *b)
 {
        Sym *e;
-       int c, d, o;
+       int c, d, o, loaded;
        Prog *p;
        Type *f;
 
@@ -566,9 +566,6 @@ genembedtramp(Type *t, Sig *b)
        fatal("genembedtramp %T.%s", t, b->name);
 
 out:
-       if(d == 0)
-               return;
-
 //     print("genembedtramp %d\n", d);
 //     print(" t    = %lT\n", t);
 //     print(" name = %s\n", b->name);
@@ -587,20 +584,24 @@ out:
        p->from.scale = 7;
 //print("1. %P\n", p);
 
-       //MOVQ  8(SP), AX
-       p = pc;
-       gins(AMOVQ, N, N);
-       p->from.type = D_INDIR+D_SP;
-       p->from.offset = 8;
-       p->to.type = D_AX;
-//print("2. %P\n", p);
-
+       loaded = 0;
        o = 0;
        for(c=d-1; c>=0; c--) {
                f = dotlist[c].field;
                o += f->width;
                if(!isptr[f->type->etype])
                        continue;
+               if(!loaded) {
+                       loaded = 1;
+                       //MOVQ  8(SP), AX
+                       p = pc;
+                       gins(AMOVQ, N, N);
+                       p->from.type = D_INDIR+D_SP;
+                       p->from.offset = 8;
+                       p->to.type = D_AX;
+//print("2. %P\n", p);
+               }
+
                //MOVQ  o(AX), AX
                p = pc;
                gins(AMOVQ, N, N);
@@ -616,17 +617,31 @@ out:
                gins(AADDQ, N, N);
                p->from.type = D_CONST;
                p->from.offset = o;
-               p->to.type = D_AX;
+               if(loaded)
+                       p->to.type = D_AX;
+               else {
+                       p->to.type = D_INDIR+D_SP;
+                       p->to.offset = 8;
+               }
 //print("4. %P\n", p);
        }
 
        //MOVQ  AX, 8(SP)
-       p = pc;
-       gins(AMOVQ, N, N);
-       p->from.type = D_AX;
-       p->to.type = D_INDIR+D_SP;
-       p->to.offset = 8;
+       if(loaded) {
+               p = pc;
+               gins(AMOVQ, N, N);
+               p->from.type = D_AX;
+               p->to.type = D_INDIR+D_SP;
+               p->to.offset = 8;
 //print("5. %P\n", p);
+       } else {
+               // TODO(rsc): obviously this is unnecessary,
+               // but 6l has a bug, and it can't handle
+               // JMP instructions too close to the top of
+               // a new function.
+               p = pc;
+               gins(ANOP, N, N);
+       }
 
        f = dotlist[0].field;
        //JMP   main·*Sub_test2(SB)