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Reduce slices correctly.

    Now, slicing creates stores/loads to the slice components. A good
    optimization opportunity would involve recognizing
        Oasn(some_slice, Oslice(some_slicable, start, end))
    But that's for another day.

    I think this is as far as I can get without rudimentary register
    allocation.

--- a/8/isel.c

+++ b/8/isel.c

@@ -39,7 +39,7 @@

 #undef Reg

 };

-const Reg reginterferes[][Nmode + 1] = {

+const Reg reginterferes[Nreg][Nmode + 1] = {

     /* byte */

     [Ral] = {Ral, Rax, Reax},

     [Rcl] = {Rcl, Rcx, Recx},

@@ -61,6 +61,8 @@

     [Rebx] = {Rbl, Rbx, Rebx},

     [Resi] = {Rsi, Resi},

     [Redi] = {Rdi, Redi},

+    [Resp] = {Resp},

+    [Rebp] = {Rebp},

 };

 char *insnfmts[] = {

@@ -699,7 +701,18 @@

             b = selexpr(s, args[0]);

             a = selexpr(s, args[1]);

             blit(s, a, b, args[2]->expr.args[0]->lit.intval);

+            r = b;

             break;

+        case Oslbase:

+            a = selexpr(s, args[0]);

+            a = inr(s, a);

+            locmem(&r, 0, a.reg, Rnone, ModeL);

+            break;

+        case Osllen:

+            a = selexpr(s, args[0]);

+            a = inr(s, a);

+            locmem(&r, 4, a.reg, Rnone, ModeL);

+            break;

         /* These operators should never show up in the reduced trees,

          * since they should have been replaced with more primitive

@@ -709,7 +722,6 @@

         case Osubeq: case Omuleq: case Odiveq: case Omodeq: case Oboreq:

         case Obandeq: case Obxoreq: case Obsleq: case Obsreq: case Omemb:

         case Oslice: case Oidx: case Osize: case Numops:

-        case Oslbase: case Osllen:

             dump(n, stdout);

             die("Should not see %s in isel", opstr(exprop(n)));

             break;

--- a/8/reduce.c

+++ b/8/reduce.c

@@ -371,6 +371,25 @@

     return r;

 }

+Node *lowerslice(Simp *s, Node *n)

+{

+    Node *t;

+    Node *base;

+    Node *len;

+    Node *stbase;

+    Node *stlen;

+

+    t = temp(s, n);

+    /* base = (void*)base + off*sz */

+    base = slicebase(s, n->expr.args[0], n->expr.args[1]);

+    len = mkexpr(-1, Osub, n->expr.args[2], n->expr.args[1], NULL);

+    stbase = mkexpr(-1, Ostor, mkexpr(-1, Oaddr, mkexpr(-1, Oslbase, t, NULL), NULL), base, NULL);

+    stlen = mkexpr(-1, Ostor, mkexpr(-1, Oaddr, mkexpr(-1, Osllen, t, NULL), NULL), len, NULL);

+    append(s, stbase);

+    append(s, stlen);

+    return t;

+}

+

 Node *rval(Simp *s, Node *n)

 {

     Node *r; /* expression result */

@@ -404,11 +423,7 @@

             r = mkexpr(-1, Olit, mkint(-1, size(args[0])), NULL);

             break;

         case Oslice:

-            /* normalize to '(base + off)[0,len]' */

-            args[0] = slicebase(s, args[0], args[1]);

-            args[2] = mkexpr(-1, Osub, args[2], args[1], NULL);

-            args[1] = mkexpr(-1, Olit, mkint(-1, 0), NULL);

-            r = n;

+            r = lowerslice(s, n);

             break;

         case Oidx:

             t = idxaddr(s, n);