cmd/gc: eliminate some pointer arithmetic

In mparith, all the a1-- are problematic. Rewrite it all without pointers.
It's clearer anyway.

In popt, v is problematic because it is used both as a fixed pointer
(v = byvar[i]) and as a moving pointer (v = var; v++) aka slice.
Eliminate pointer movement.

Tested that this still produces bit-for-bit output for 'go build -a std'
compared to d260756 (current master).

Change-Id: I1a1bed0f98b594c3864fe95075dd95f9b52113e0
Reviewed-on: https://go-review.googlesource.com/4645
Reviewed-by: Austin Clements <austin@google.com>

diff --git a/src/cmd/gc/mparith1.c b/src/cmd/gc/mparith1.c
index d85dc73bd95aa194f455b5835bdf7c1d0d71a51d..6a0eb2d6d9da1c725b02629f733e342ebc18832b 100644 (file)
--- a/src/cmd/gc/mparith1.c
+++ b/src/cmd/gc/mparith1.c
@@ -235,9 +235,9 @@ mppow10flt(Mpflt *a, int p)
 static void
 mphextofix(Mpint *a, char *s, int n)
 {
-       char *hexdigitp, *end, c;
+       char c;
        long d;
-       int bit;
+       int bit, hexdigitp, end;
 
        while(*s == '0') {
                s++;
@@ -250,9 +250,9 @@ mphextofix(Mpint *a, char *s, int n)
                return;
        }
 
-       end = s+n-1;
-       for(hexdigitp=end; hexdigitp>=s; hexdigitp--) {
-               c = *hexdigitp;
+       end = n-1;
+       for(hexdigitp=end; hexdigitp>=0; hexdigitp--) {
+               c = s[hexdigitp];
                if(c >= '0' && c <= '9')
                        d = c-'0';
                else if(c >= 'A' && c <= 'F')
@@ -348,7 +348,8 @@ mpatoflt(Mpflt *a, char *as)
                mpnorm(a);
        }
        for(;;) {
-               switch(c = *s++) {
+               c = *s++;
+               switch(c) {
                default:
                        yyerror("malformed constant: %s (at %c)", as, c);
                        goto bad;
@@ -542,7 +543,8 @@ bad:
 int
 Bconv(Fmt *fp)
 {
-       char buf[500], *p;
+       char buf[500];
+       int p;
        Mpint *xval, q, r, ten, sixteen;
        int f, digit;
 
@@ -554,8 +556,8 @@ Bconv(Fmt *fp)
                mpnegfix(&q);
        }
 
-       p = &buf[sizeof(buf)];
-       *--p = 0;
+       p = sizeof(buf);
+       buf[--p] = 0;
        if(fp->flags & FmtSharp) {
                // Hexadecimal
                mpmovecfix(&sixteen, 16);
@@ -563,27 +565,27 @@ Bconv(Fmt *fp)
                        mpdivmodfixfix(&q, &r, &q, &sixteen);
                        digit = mpgetfix(&r);
                        if(digit < 10)
-                               *--p = digit + '0';
+                               buf[--p] = digit + '0';
                        else
-                               *--p = digit - 10 + 'A';
+                               buf[--p] = digit - 10 + 'A';
                        if(mptestfix(&q) <= 0)
                                break;
                }
-               *--p = 'x';
-               *--p = '0';
+               buf[--p] = 'x';
+               buf[--p] = '0';
        } else {
                // Decimal
                mpmovecfix(&ten, 10);
                for(;;) {
                        mpdivmodfixfix(&q, &r, &q, &ten);
-                       *--p = mpgetfix(&r) + '0';
+                       buf[--p] = mpgetfix(&r) + '0';
                        if(mptestfix(&q) <= 0)
                                break;
                }
        }
        if(f)
-               *--p = '-';
-       return fmtstrcpy(fp, p);
+               buf[--p] = '-';
+       return fmtstrcpy(fp, &buf[p]);
 }
 
 int

diff --git a/src/cmd/gc/mparith2.c b/src/cmd/gc/mparith2.c
index fd9f591ceae2ac164b48b6be4ffdad8a04af04b4..37aafbb5f53ad55c57928930c523b91000a7ff81 100644 (file)
--- a/src/cmd/gc/mparith2.c
+++ b/src/cmd/gc/mparith2.c
@@ -14,12 +14,10 @@ static int
 mplen(Mpint *a)
 {
        int i, n;
-       long *a1;
 
        n = -1;
-       a1 = &a->a[0];
        for(i=0; i<Mpprec; i++) {
-               if(*a1++ != 0)
+               if(a->a[i] != 0)
                        n = i;
        }
        return n+1;
@@ -32,19 +30,18 @@ mplen(Mpint *a)
 static void
 mplsh(Mpint *a, int quiet)
 {
-       long *a1, x;
+       long x;
        int i, c;
 
        c = 0;
-       a1 = &a->a[0];
        for(i=0; i<Mpprec; i++) {
-               x = (*a1 << 1) + c;
+               x = (a->a[i] << 1) + c;
                c = 0;
                if(x >= Mpbase) {
                        x -= Mpbase;
                        c = 1;
                }
-               *a1++ = x;
+               a->a[i] = x;
        }
        a->ovf = c;
        if(a->ovf && !quiet)
@@ -58,20 +55,17 @@ mplsh(Mpint *a, int quiet)
 static void
 mplshw(Mpint *a, int quiet)
 {
-       long *a1;
        int i;
 
-       a1 = &a->a[Mpprec-1];
-       if(*a1) {
+       i = Mpprec-1;
+       if(a->a[i]) {
                a->ovf = 1;
                if(!quiet)
                        yyerror("constant shift overflow");
        }
-       for(i=1; i<Mpprec; i++) {
-               a1[0] = a1[-1];
-               a1--;
-       }
-       a1[0] = 0;
+       for(; i > 0; i--)
+               a->a[i] = a->a[i-1];
+       a->a[i] = 0;
 }
 
 //
@@ -81,15 +75,14 @@ mplshw(Mpint *a, int quiet)
 static void
 mprsh(Mpint *a)
 {
-       long *a1, x, lo;
+       long x, lo;
        int i, c;
 
        c = 0;
        lo = a->a[0] & 1;
-       a1 = &a->a[Mpprec];
-       for(i=0; i<Mpprec; i++) {
-               x = *--a1;
-               *a1 = (x + c) >> 1;
+       for(i=Mpprec-1; i>=0; i--) {
+               x = a->a[i];
+               a->a[i] = (x + c) >> 1;
                c = 0;
                if(x & 1)
                        c = Mpbase;
@@ -105,16 +98,14 @@ mprsh(Mpint *a)
 static void
 mprshw(Mpint *a)
 {
-       long *a1, lo;
+       long lo;
        int i;
 
        lo = a->a[0];
-       a1 = &a->a[0];
-       for(i=1; i<Mpprec; i++) {
-               a1[0] = a1[1];
-               a1++;
+       for(i=0; i<Mpprec-1; i++) {
+               a->a[i] = a->a[i+1];
        }
-       a1[0] = 0;
+       a->a[i] = 0;
        if(a->neg && lo != 0)
                mpaddcfix(a, -1);
 }
@@ -125,7 +116,7 @@ mprshw(Mpint *a)
 static int
 mpcmp(Mpint *a, Mpint *b)
 {
-       long x, *a1, *b1;
+       long x;
        int i;
 
        if(a->ovf || b->ovf) {
@@ -134,11 +125,8 @@ mpcmp(Mpint *a, Mpint *b)
                return 0;
        }
 
-       a1 = &a->a[0] + Mpprec;
-       b1 = &b->a[0] + Mpprec;
-
-       for(i=0; i<Mpprec; i++) {
-               x = *--a1 - *--b1;
+       for(i=Mpprec-1; i>=0; i--) {
+               x = a->a[i] - b->a[i];
                if(x > 0)
                        return +1;
                if(x < 0)
@@ -154,19 +142,18 @@ mpcmp(Mpint *a, Mpint *b)
 static void
 mpneg(Mpint *a)
 {
-       long x, *a1;
+       long x;
        int i, c;
 
-       a1 = &a->a[0];
        c = 0;
        for(i=0; i<Mpprec; i++) {
-               x = -*a1 -c;
+               x = -a->a[i] -c;
                c = 0;
                if(x < 0) {
                        x += Mpbase;
                        c = 1;
                }
-               *a1++ = x;
+               a->a[i] = x;
        }
 }
 
@@ -202,7 +189,7 @@ void
 mpaddfixfix(Mpint *a, Mpint *b, int quiet)
 {
        int i, c;
-       long x, *a1, *b1;
+       long x;
 
        if(a->ovf || b->ovf) {
                if(nsavederrors+nerrors == 0)
@@ -212,20 +199,18 @@ mpaddfixfix(Mpint *a, Mpint *b, int quiet)
        }
 
        c = 0;
-       a1 = &a->a[0];
-       b1 = &b->a[0];
        if(a->neg != b->neg)
                goto sub;
 
        // perform a+b
        for(i=0; i<Mpprec; i++) {
-               x = *a1 + *b1++ + c;
+               x = a->a[i] + b->a[i] + c;
                c = 0;
                if(x >= Mpbase) {
                        x -= Mpbase;
                        c = 1;
                }
-               *a1++ = x;
+               a->a[i] = x;
        }
        a->ovf = c;
        if(a->ovf && !quiet)
@@ -242,26 +227,26 @@ sub:
 
        case 1:
                for(i=0; i<Mpprec; i++) {
-                       x = *a1 - *b1++ - c;
+                       x = a->a[i] - b->a[i] - c;
                        c = 0;
                        if(x < 0) {
                                x += Mpbase;
                                c = 1;
                        }
-                       *a1++ = x;
+                       a->a[i] = x;
                }
                break;
 
        case -1:
                a->neg ^= 1;
                for(i=0; i<Mpprec; i++) {
-                       x = *b1++ - *a1 - c;
+                       x = b->a[i] - a->a[i] - c;
                        c = 0;
                        if(x < 0) {
                                x += Mpbase;
                                c = 1;
                        }
-                       *a1++ = x;
+                       a->a[i] = x;
                }
                break;
        }
@@ -272,8 +257,9 @@ mpmulfixfix(Mpint *a, Mpint *b)
 {
 
        int i, j, na, nb;
-       long *a1, x;
+       long x;
        Mpint s, q;
+       Mpint *c;
 
        if(a->ovf || b->ovf) {
                if(nsavederrors+nerrors == 0)
@@ -288,17 +274,17 @@ mpmulfixfix(Mpint *a, Mpint *b)
        nb = mplen(b);
        if(na > nb) {
                mpmovefixfix(&s, a);
-               a1 = &b->a[0];
+               c = b;
                na = nb;
        } else {
                mpmovefixfix(&s, b);
-               a1 = &a->a[0];
+               c = a;
        }
        s.neg = 0;
 
        mpmovecfix(&q, 0);
        for(i=0; i<na; i++) {
-               x = *a1++;
+               x = c->a[i];
                for(j=0; j<Mpscale; j++) {
                        if(x & 1) {
                                if(s.ovf) {
@@ -326,7 +312,7 @@ mpmulfract(Mpint *a, Mpint *b)
 {
 
        int i, j;
-       long *a1, x;
+       long x;
        Mpint s, q;
 
        if(a->ovf || b->ovf) {
@@ -337,16 +323,16 @@ mpmulfract(Mpint *a, Mpint *b)
        }
 
        mpmovefixfix(&s, b);
-       a1 = &a->a[Mpprec];
        s.neg = 0;
        mpmovecfix(&q, 0);
 
-       x = *--a1;
+       i = Mpprec-1;
+       x = a->a[i];
        if(x != 0)
                yyerror("mpmulfract not normal");
 
-       for(i=0; i<Mpprec-1; i++) {
-               x = *--a1;
+       for(i--; i >= 0; i--) {
+               x = a->a[i];
                if(x == 0) {
                        mprshw(&s);
                        continue;
@@ -369,7 +355,7 @@ void
 mporfixfix(Mpint *a, Mpint *b)
 {
        int i;
-       long x, *a1, *b1;
+       long x;
 
        x = 0;
        if(a->ovf || b->ovf) {
@@ -386,11 +372,9 @@ mporfixfix(Mpint *a, Mpint *b)
        if(b->neg)
                mpneg(b);
 
-       a1 = &a->a[0];
-       b1 = &b->a[0];
        for(i=0; i<Mpprec; i++) {
-               x = *a1 | *b1++;
-               *a1++ = x;
+               x = a->a[i] | b->a[i];
+               a->a[i] = x;
        }
 
        if(b->neg)
@@ -405,7 +389,7 @@ void
 mpandfixfix(Mpint *a, Mpint *b)
 {
        int i;
-       long x, *a1, *b1;
+       long x;
 
        x = 0;
        if(a->ovf || b->ovf) {
@@ -422,11 +406,9 @@ mpandfixfix(Mpint *a, Mpint *b)
        if(b->neg)
                mpneg(b);
 
-       a1 = &a->a[0];
-       b1 = &b->a[0];
        for(i=0; i<Mpprec; i++) {
-               x = *a1 & *b1++;
-               *a1++ = x;
+               x = a->a[i] & b->a[i];
+               a->a[i] = x;
        }
 
        if(b->neg)
@@ -441,7 +423,7 @@ void
 mpandnotfixfix(Mpint *a, Mpint *b)
 {
        int i;
-       long x, *a1, *b1;
+       long x;
 
        x = 0;
        if(a->ovf || b->ovf) {
@@ -458,11 +440,9 @@ mpandnotfixfix(Mpint *a, Mpint *b)
        if(b->neg)
                mpneg(b);
 
-       a1 = &a->a[0];
-       b1 = &b->a[0];
        for(i=0; i<Mpprec; i++) {
-               x = *a1 & ~*b1++;
-               *a1++ = x;
+               x = a->a[i] & ~b->a[i];
+               a->a[i] = x;
        }
 
        if(b->neg)
@@ -477,7 +457,7 @@ void
 mpxorfixfix(Mpint *a, Mpint *b)
 {
        int i;
-       long x, *a1, *b1;
+       long x;
 
        x = 0;
        if(a->ovf || b->ovf) {
@@ -494,11 +474,9 @@ mpxorfixfix(Mpint *a, Mpint *b)
        if(b->neg)
                mpneg(b);
 
-       a1 = &a->a[0];
-       b1 = &b->a[0];
        for(i=0; i<Mpprec; i++) {
-               x = *a1 ^ *b1++;
-               *a1++ = x;
+               x = a->a[i] ^ b->a[i];
+               a->a[i] = x;
        }
 
        if(b->neg)
@@ -585,7 +563,6 @@ void
 mpmovecfix(Mpint *a, vlong c)
 {
        int i;
-       long *a1;
        vlong x;
 
        a->neg = 0;
@@ -597,9 +574,8 @@ mpmovecfix(Mpint *a, vlong c)
                x = -(uvlong)x;
        }
 
-       a1 = &a->a[0];
        for(i=0; i<Mpprec; i++) {
-               *a1++ = x&Mpmask;
+               a->a[i] = x&Mpmask;
                x >>= Mpscale;
        }
 }
@@ -658,13 +634,11 @@ mpdivmodfixfix(Mpint *q, Mpint *r, Mpint *n, Mpint *d)
 static int
 mpiszero(Mpint *a)
 {
-       long *a1;
        int i;
-       a1 = &a->a[0] + Mpprec;
-       for(i=0; i<Mpprec; i++) {
-               if(*--a1 != 0)
+
+       for(i=Mpprec-1; i>=0; i--)
+               if(a->a[i] != 0)
                        return 0;
-       }
        return 1;
 }
 
@@ -673,16 +647,15 @@ mpdivfract(Mpint *a, Mpint *b)
 {
        Mpint n, d;
        int i, j, neg;
-       long *a1, x;
+       long x;
 
        mpmovefixfix(&n, a);    // numerator
        mpmovefixfix(&d, b);    // denominator
-       a1 = &a->a[Mpprec];     // quotient
 
        neg = n.neg ^ d.neg;
        n.neg = 0;
        d.neg = 0;
-       for(i=0; i<Mpprec; i++) {
+       for(i=Mpprec-1; i >= 0; i--) {
                x = 0;
                for(j=0; j<Mpscale; j++) {
                        x <<= 1;
@@ -693,7 +666,7 @@ mpdivfract(Mpint *a, Mpint *b)
                        }
                        mprsh(&d);
                }
-               *--a1 = x;
+               a->a[i] = x;
        }
        a->neg = neg;
 }

diff --git a/src/cmd/gc/popt.c b/src/cmd/gc/popt.c
index 83f155564a39ae4fa0f972c70cb78200532f0a96..af7e5b1ff337c036beb9664d6b6bff3dadc9c1d3 100644 (file)
--- a/src/cmd/gc/popt.c
+++ b/src/cmd/gc/popt.c
@@ -618,7 +618,8 @@ mergetemp(Prog *firstp)
        nkill = 0;
 
        // Special case.
-       for(v = var; v < var+nvar; v++) {
+       for(i = 0; i < nvar; i++) {
+               v = &var[i];
                if(v->addr)
                        continue;
                // Used in only one instruction, which had better be a write.
@@ -665,7 +666,8 @@ mergetemp(Prog *firstp)
        // Each flood uses a new value of gen so that we don't have
        // to clear all the r->active words after each variable.
        gen = 0;
-       for(v = var; v < var+nvar; v++) {
+       for(i = 0; i < nvar; i++) {
+               v = &var[i];
                gen++;
                for(f = v->use; f != nil; f = (Flow*)f->data)
                        mergewalk(v, f, gen);
@@ -740,7 +742,8 @@ mergetemp(Prog *firstp)
 
        if(debugmerge > 0 && debug['v']) {
                print("%S [%d - %d]\n", curfn->nname->sym, nvar, nkill);
-               for(v=var; v<var+nvar; v++) {
+               for(i = 0; i < nvar; i++) {
+                       v = &var[i];
                        print("var %#N %T %lld-%lld", v->node, v->node->type, v->start, v->end);
                        if(v->addr)
                                print(" addr=1");
@@ -779,8 +782,10 @@ mergetemp(Prog *firstp)
        }
 
        // Clear aux structures.
-       for(v=var; v<var+nvar; v++)
+       for(i = 0; i < nvar; i++) {
+               v = &var[i];
                v->node->opt = nil;
+       }
        free(var);
        free(bystart);
        free(inuse);

diff --git a/src/cmd/gc/reg.c b/src/cmd/gc/reg.c
index 878705bd850becb234deaf9c8a0b94d81a149e06..67409c21271b25387b96a3e97c2dfd9a924d6450 100644 (file)
--- a/src/cmd/gc/reg.c
+++ b/src/cmd/gc/reg.c
@@ -103,6 +103,7 @@ regopt(Prog *firstp)
        int nreg;
        char **regnames;
        Bits bit;
+       Rgn *rgp;
 
        if(first) {
                fmtinstall('Q', Qconv);
@@ -198,7 +199,8 @@ regopt(Prog *firstp)
        }
 
        for(i=0; i<nvar; i++) {
-               Var *v = var+i;
+               Var *v;
+               v = var+i;
                if(v->addr) {
                        bit = blsh(i);
                        for(z=0; z<BITS; z++)
@@ -206,7 +208,7 @@ regopt(Prog *firstp)
                }
 
                if(debug['R'] && debug['v'])
-                       print("bit=%2d addr=%d et=%-6E w=%-2d s=%N + %lld\n",
+                       print("bit=%2d addr=%d et=%E w=%-2d s=%N + %lld\n",
                                i, v->addr, v->etype, v->width, v->node, v->offset);
        }
 
@@ -334,7 +336,6 @@ loop2:
        }
        for(f = firstf; f != nil; f = f->link)
                ((Reg*)f->data)->act = zbits;
-       rgp = region;
        nregion = 0;
        for(f = firstf; f != nil; f = f->link) {
                r = (Reg*)f->data;
@@ -361,10 +362,10 @@ loop2:
                                        print("too many regions\n");
                                goto brk;
                        }
+                       rgp = &region[nregion];
                        rgp->enter = f;
                        rgp->varno = i;
                        rgp->cost = change;
-                       rgp++;
                        nregion++;
                }
        }
@@ -379,10 +380,10 @@ brk:
         * determine used registers (paint2)
         * replace code (paint3)
         */
-       rgp = region;
        if(debug['R'] && debug['v'])
                print("\nregisterizing\n");
        for(i=0; i<nregion; i++) {
+               rgp = &region[i];
                if(debug['R'] && debug['v'])
                        print("region %d: cost %d varno %d enter %lld\n", i, rgp->cost, rgp->varno, rgp->enter->prog->pc);
                bit = blsh(rgp->varno);
@@ -393,12 +394,11 @@ brk:
                                Var *v;
 
                                v = var + rgp->varno;
-                               print("registerize %N+%lld (bit=%2d et=%2E) in %R usedreg=%#llx vreg=%#llx\n",
+                               print("registerize %N+%lld (bit=%2d et=%E) in %R usedreg=%#llx vreg=%#llx\n",
                                                v->node, v->offset, rgp->varno, v->etype, rgp->regno, usedreg, vreg);
                        }
                        paint3(rgp->enter, rgp->varno, vreg, rgp->regno);
                }
-               rgp++;
        }
 
        /*
@@ -477,7 +477,7 @@ walkvardef(Node *n, Flow *f, int active)
                if(f1->prog->as == AVARKILL && f1->prog->to.node == n)
                        break;
                for(v=n->opt; v!=nil; v=v->nextinnode) {
-                       bn = v - var;
+                       bn = v->id;
                        biset(&((Reg*)f1->data)->act, bn);
                }
                if(f1->prog->as == ACALL)
@@ -680,6 +680,7 @@ mkvar(Flow *f, Adr *a)
        i = nvar;
        nvar++;
        v = var+i;
+       v->id = i;
        v->offset = o;
        v->name = n;
        v->etype = et;
@@ -739,7 +740,7 @@ mkvar(Flow *f, Adr *a)
                v->addr = 1;
 
        if(debug['R'])
-               print("bit=%2d et=%2E w=%lld+%lld %#N %D flag=%d\n", i, et, o, w, node, a, v->addr);
+               print("bit=%2d et=%E w=%lld+%lld %#N %D flag=%d\n", i, et, o, w, node, a, v->addr);
        ostats.nvar++;
 
        return bit;
@@ -753,7 +754,7 @@ prop(Flow *f, Bits ref, Bits cal)
 {
        Flow *f1, *f2;
        Reg *r, *r1;
-       int z, i, j;
+       int z, i;
        Var *v, *v1;
 
        for(f1 = f; f1 != nil; f1 = f1->p1) {
@@ -820,11 +821,9 @@ prop(Flow *f, Bits ref, Bits cal)
                                        // v is the head of the list or if the head's bit is not yet turned on.
                                        // This will set the bits at most twice, keeping the overall loop linear.
                                        v1 = v->node->opt;
-                                       j = v1 - var;
-                                       if(v == v1 || !btest(&cal, j)) {
+                                       if(v == v1 || !btest(&cal, v1->id)) {
                                                for(; v1 != nil; v1 = v1->nextinnode) {
-                                                       j = v1 - var;
-                                                       biset(&cal, j);
+                                                       biset(&cal, v1->id);
                                                }
                                        }
                                }