part 2 of sudoaddable optimization

R=rsc
CC=golang-dev
https://golang.org/cl/190088

diff --git a/src/cmd/6g/gsubr.c b/src/cmd/6g/gsubr.c
index 4d17bb8a24ed4966411dfcc00b811030c7c8500a..aad5ff03f107faa4e4de17e564704e715b274db0 100644 (file)
--- a/src/cmd/6g/gsubr.c
+++ b/src/cmd/6g/gsubr.c
@@ -1880,7 +1880,17 @@ oindex_const:
        // can check statically and
        // can multiply by width statically
 
-       if((o & ODynam) == 0)
+       v = mpgetfix(r->val.u.xval);
+       if(!debug['B'] && (o & ODynam) == 0) {
+               // array indexed by a constant bounds check
+               if(v < 0) {
+                       yyerror("out of bounds on array");
+               } else
+               if(v >= l->type->bound) {
+                       yyerror("out of bounds on array");
+               }
+       }
+
        if(sudoaddable(as, l, a))
                goto oindex_const_sudo;
 
@@ -1893,7 +1903,6 @@ oindex_const:
        regalloc(reg, types[tptr], N);
        agen(l, reg);
 
-       v = mpgetfix(r->val.u.xval);
        if(o & ODynam) {
                if(!debug['B'] && !n->etype) {
                        n1 = *reg;
@@ -1913,14 +1922,6 @@ oindex_const:
                n1.xoffset = Array_array;
                gmove(&n1, reg);
 
-       } else
-       if(!debug['B']) {
-               if(v < 0) {
-                       yyerror("out of bounds on array");
-               } else
-               if(v >= l->type->bound) {
-                       yyerror("out of bounds on array");
-               }
        }
 
        n2 = *reg;
@@ -1932,14 +1933,38 @@ oindex_const:
        goto yes;
 
 oindex_const_sudo:
-       v = mpgetfix(r->val.u.xval);
-       if(v < 0) {
-               yyerror("out of bounds on array");
-       } else
-       if(v >= l->type->bound) {
-               yyerror("out of bounds on array");
+       if((o & ODynam) == 0) {
+               // array indexed by a constant
+               a->offset += v*w;
+               goto yes;
        }
-       a->offset += v*w;
+
+       // slice indexed by a constant
+       if(!debug['B'] && !n->etype) {
+               a->offset += Array_nel;
+               nodconst(&n2, types[TUINT64], v);
+               p1 = gins(optoas(OCMP, types[TUINT32]), N, &n2);
+               p1->from = *a;
+               p1 = gbranch(optoas(OGT, types[TUINT32]), T);
+               ginscall(throwindex, 0);
+               patch(p1, pc);
+               a->offset -= Array_nel;
+       }
+
+       a->offset += Array_array;
+       reg = &clean[cleani-1];
+       if(reg->op == OEMPTY)
+               regalloc(reg, types[tptr], N);
+
+       p1 = gins(AMOVQ, N, reg);
+       p1->from = *a;
+
+       n2 = *reg;
+       n2.op = OINDREG;
+       n2.xoffset = v*w;
+       a->type = D_NONE;
+       a->index = D_NONE;
+       naddr(&n2, a, 1);
        goto yes;
 
 yes: