Some useful warnings.
 [rsc] --rw-rw-r-- M 84741 glenda sys 12122 Dec 11 12:22 sys/src/cmd/cc/cc.h
	/n/sourcesdump/2005/1211/plan9/sys/src/cmd/cc/cc.h:57,62 - 
	/n/sourcesdump/2005/1212/plan9/sys/src/cmd/cc/cc.h:57,64
	  	Type*	type;
	  	long	lineno;
	  	char	op;
	+ 	char	oldop;
	+ 	char xcast;
	  	char	class;
	  	char	etype;
	  	char	complex;
	/n/sourcesdump/2005/1211/plan9/sys/src/cmd/cc/cc.h:497,502 - 
	/n/sourcesdump/2005/1212/plan9/sys/src/cmd/cc/cc.h:499,505
	  extern	char	typeilp[];
	  extern	char	typechl[];
	  extern	char	typechlv[];
	+ extern	char	typechlvp[];
	  extern	char	typechlp[];
	  extern	char	typechlpfd[];
	  
 [rsc] --rw-rw-r-- M 84741 glenda sys 16058 Dec 11 12:21 sys/src/cmd/cc/cc.y
	/n/sourcesdump/2005/1211/plan9/sys/src/cmd/cc/cc.y:656,661 - 
	/n/sourcesdump/2005/1212/plan9/sys/src/cmd/cc/cc.y:656,662
	  		$$ = new(OCAST, $5, Z);
	  		dodecl(NODECL, CXXX, $2, $3);
	  		$$->type = lastdcl;
	+ 		$$->xcast = 1;
	  	}
	  |	'(' tlist abdecor ')' '{' ilist '}'	/* extension */
	  	{
	/n/sourcesdump/2005/1211/plan9/sys/src/cmd/cc/cc.y:760,765 - 
	/n/sourcesdump/2005/1212/plan9/sys/src/cmd/cc/cc.y:761,767
	  		$$ = new(OCONST, Z, Z);
	  		$$->type = types[TINT];
	  		$$->vconst = $1;
	+ 		$$->cstring = strdup(symb);
	  	}
	  |	LLCONST
	  	{
	/n/sourcesdump/2005/1211/plan9/sys/src/cmd/cc/cc.y:766,771 - 
	/n/sourcesdump/2005/1212/plan9/sys/src/cmd/cc/cc.y:768,774
	  		$$ = new(OCONST, Z, Z);
	  		$$->type = types[TLONG];
	  		$$->vconst = $1;
	+ 		$$->cstring = strdup(symb);
	  	}
	  |	LUCONST
	  	{
	/n/sourcesdump/2005/1211/plan9/sys/src/cmd/cc/cc.y:772,777 - 
	/n/sourcesdump/2005/1212/plan9/sys/src/cmd/cc/cc.y:775,781
	  		$$ = new(OCONST, Z, Z);
	  		$$->type = types[TUINT];
	  		$$->vconst = $1;
	+ 		$$->cstring = strdup(symb);
	  	}
	  |	LULCONST
	  	{
	/n/sourcesdump/2005/1211/plan9/sys/src/cmd/cc/cc.y:778,783 - 
	/n/sourcesdump/2005/1212/plan9/sys/src/cmd/cc/cc.y:782,788
	  		$$ = new(OCONST, Z, Z);
	  		$$->type = types[TULONG];
	  		$$->vconst = $1;
	+ 		$$->cstring = strdup(symb);
	  	}
	  |	LDCONST
	  	{
	/n/sourcesdump/2005/1211/plan9/sys/src/cmd/cc/cc.y:784,789 - 
	/n/sourcesdump/2005/1212/plan9/sys/src/cmd/cc/cc.y:789,795
	  		$$ = new(OCONST, Z, Z);
	  		$$->type = types[TDOUBLE];
	  		$$->fconst = $1;
	+ 		$$->cstring = strdup(symb);
	  	}
	  |	LFCONST
	  	{
	/n/sourcesdump/2005/1211/plan9/sys/src/cmd/cc/cc.y:790,795 - 
	/n/sourcesdump/2005/1212/plan9/sys/src/cmd/cc/cc.y:796,802
	  		$$ = new(OCONST, Z, Z);
	  		$$->type = types[TFLOAT];
	  		$$->fconst = $1;
	+ 		$$->cstring = strdup(symb);
	  	}
	  |	LVLCONST
	  	{
	/n/sourcesdump/2005/1211/plan9/sys/src/cmd/cc/cc.y:796,801 - 
	/n/sourcesdump/2005/1212/plan9/sys/src/cmd/cc/cc.y:803,809
	  		$$ = new(OCONST, Z, Z);
	  		$$->type = types[TVLONG];
	  		$$->vconst = $1;
	+ 		$$->cstring = strdup(symb);
	  	}
	  |	LUVLCONST
	  	{
	/n/sourcesdump/2005/1211/plan9/sys/src/cmd/cc/cc.y:802,807 - 
	/n/sourcesdump/2005/1212/plan9/sys/src/cmd/cc/cc.y:810,816
	  		$$ = new(OCONST, Z, Z);
	  		$$->type = types[TUVLONG];
	  		$$->vconst = $1;
	+ 		$$->cstring = strdup(symb);
	  	}
	  |	string
	  |	lstring
 [rsc] --rw-rw-r-- M 84741 glenda sys 22202 Dec 11 12:22 sys/src/cmd/cc/com.c
	/n/sourcesdump/2005/1211/plan9/sys/src/cmd/cc/com.c:1,5 - 
	/n/sourcesdump/2005/1212/plan9/sys/src/cmd/cc/com.c:1,7
	  #include "cc.h"
	  
	+ int compar(Node*, int);
	+ 
	  void
	  complex(Node *n)
	  {
	/n/sourcesdump/2005/1211/plan9/sys/src/cmd/cc/com.c:985,990 - 
	/n/sourcesdump/2005/1212/plan9/sys/src/cmd/cc/com.c:987,994
	  	case OHI:
	  		ccom(l);
	  		ccom(r);
	+ 		if(compar(n, 0) || compar(n, 1))
	+ 			break;
	  		relcon(l, r);
	  		relcon(r, l);
	  		goto common;
	/n/sourcesdump/2005/1211/plan9/sys/src/cmd/cc/com.c:1082,1088 - 
	/n/sourcesdump/2005/1212/plan9/sys/src/cmd/cc/com.c:1086,1092
	  			*n = *l;
	  			break;
	  		}
	- 		goto commun;
	+ 		goto commute;
	  
	  	case OAND:
	  		ccom(l);
	/n/sourcesdump/2005/1211/plan9/sys/src/cmd/cc/com.c:1096,1102 - 
	/n/sourcesdump/2005/1212/plan9/sys/src/cmd/cc/com.c:1100,1106
	  			break;
	  		}
	  
	- 	commun:
	+ 	commute:
	  		/* look for commutative constant */
	  		if(r->op == OCONST) {
	  			if(l->op == n->op) {
	/n/sourcesdump/2005/1211/plan9/sys/src/cmd/cc/com.c:1162,1164 - 
	/n/sourcesdump/2005/1212/plan9/sys/src/cmd/cc/com.c:1166,1346
	  		evconst(n);
	  	}
	  }
	+ 
	+ /*	OEQ, ONE, OLE, OLS, OLT, OLO, OGE, OHS, OGT, OHI */
	+ static char *cmps[12] = 
	+ {
	+ 	"==", "!=", "<=", "<=", "<", "<", ">=", ">=", ">", ">",
	+ };
	+ 
	+ /* 128-bit numbers */
	+ typedef struct Big Big;
	+ struct Big
	+ {
	+ 	vlong a;
	+ 	uvlong b;
	+ };
	+ static int
	+ cmp(Big x, Big y)
	+ {
	+ 	if(x.a != y.a){
	+ 		if(x.a < y.a)
	+ 			return -1;
	+ 		return 1;
	+ 	}
	+ 	if(x.b != y.b){
	+ 		if(x.b < y.b)
	+ 			return -1;
	+ 		return 1;
	+ 	}
	+ 	return 0;
	+ }
	+ static Big
	+ add(Big x, int y)
	+ {
	+ 	uvlong ob;
	+ 	
	+ 	ob = x.b;
	+ 	x.b += y;
	+ 	if(y > 0 && x.b < ob)
	+ 		x.a++;
	+ 	if(y < 0 && x.b > ob)
	+ 		x.a--;
	+ 	return x;
	+ } 
	+ 
	+ Big
	+ big(vlong a, uvlong b)
	+ {
	+ 	Big x;
	+ 
	+ 	x.a = a;
	+ 	x.b = b;
	+ 	return x;
	+ }
	+ 
	+ int
	+ compar(Node *n, int reverse)
	+ {
	+ 	Big lo, hi, x;
	+ 	int op;
	+ 	char xbuf[40], cmpbuf[50];
	+ 	Node *l, *r;
	+ 	Type *lt, *rt;
	+ 
	+ 	/*
	+ 	 * The point of this function is to diagnose comparisons 
	+ 	 * that can never be true or that look misleading because
	+ 	 * of the `usual arithmetic conversions'.  As an example 
	+ 	 * of the latter, if x is a ulong, then if(x <= -1) really means
	+ 	 * if(x <= 0xFFFFFFFF), while if(x <= -1LL) really means
	+ 	 * what it says (but 8c compiles it wrong anyway).
	+ 	 */
	+ 
	+ 	if(reverse){
	+ 		r = n->left;
	+ 		l = n->right;
	+ 		op = comrel[relindex(n->op)];
	+ 	}else{
	+ 		l = n->left;
	+ 		r = n->right;
	+ 		op = n->op;
	+ 	}
	+ 
	+ 	/*
	+ 	 * Skip over left casts to find out the original expression range.
	+ 	 */
	+ 	while(l->op == OCAST)
	+ 		l = l->left;
	+ 	if(l->op == OCONST)
	+ 		return 0;
	+ 	lt = l->type;
	+ 	if(l->op == ONAME){
	+ 		lt = l->sym->type;
	+ 		if(lt && lt->etype == TARRAY)
	+ 			lt = lt->link;
	+ 	}
	+ 	if(lt == T)
	+ 		return 0;
	+ 	if(lt->etype == TXXX || lt->etype > TUVLONG)
	+ 		return 0;
	+ 	
	+ 	/*
	+ 	 * Skip over the right casts to find the on-screen value.
	+ 	 */
	+ 	if(r->op != OCONST)
	+ 		return 0;
	+ 	while(r->oldop == OCAST && !r->xcast)
	+ 		r = r->left;
	+ 	rt = r->type;
	+ 	if(rt == T)
	+ 		return 0;
	+ 
	+ 	x.b = r->vconst;
	+ 	x.a = 0;
	+ 	if((rt->etype&1) && r->vconst < 0)	/* signed negative */
	+ 		x.a = ~0ULL;
	+ 
	+ 	if((lt->etype&1)==0){
	+ 		/* unsigned */
	+ 		lo = big(0, 0);
	+ 		if(lt->width == 8)
	+ 			hi = big(0, ~0ULL);
	+ 		else
	+ 			hi = big(0, (1LL<<(l->type->width*8))-1);
	+ 	}else{
	+ 		lo = big(~0ULL, -(1LL<<(l->type->width*8-1)));
	+ 		hi = big(0, (1LL<<(l->type->width*8-1))-1);
	+ 	}
	+ 
	+ 	switch(op){
	+ 	case OLT:
	+ 	case OLO:
	+ 	case OGE:
	+ 	case OHS:
	+ 		if(cmp(x, lo) <= 0)
	+ 			goto useless;
	+ 		if(cmp(x, add(hi, 1)) >= 0)
	+ 			goto useless;
	+ 		break;
	+ 	case OLE:
	+ 	case OLS:
	+ 	case OGT:
	+ 	case OHI:
	+ 		if(cmp(x, add(lo, -1)) <= 0)
	+ 			goto useless;
	+ 		if(cmp(x, hi) >= 0)
	+ 			goto useless;
	+ 		break;
	+ 	case OEQ:
	+ 	case ONE:
	+ 		/*
	+ 		 * Don't warn about comparisons if the expression
	+ 		 * is as wide as the value: the compiler-supplied casts
	+ 		 * will make both outcomes possible.
	+ 		 */
	+ 		if(lt->width >= rt->width && debug['w'] < 2)
	+ 			return 0;
	+ 		if(cmp(x, lo) < 0 || cmp(x, hi) > 0)
	+ 			goto useless;
	+ 		break;
	+ 	}
	+ 	return 0;
	+ 
	+ useless:
	+ 	if((x.a==0 && x.b<=9) || (x.a==~0LL && x.b >= -9ULL))
	+ 		snprint(xbuf, sizeof xbuf, "%lld", x.b);
	+ 	else if(x.a == 0)
	+ 		snprint(xbuf, sizeof xbuf, "%#llux", x.b);
	+ 	else
	+ 		snprint(xbuf, sizeof xbuf, "%#llx", x.b);
	+ 	if(reverse)
	+ 		snprint(cmpbuf, sizeof cmpbuf, "%s %s %T",
	+ 			xbuf, cmps[relindex(n->op)], lt);
	+ 	else
	+ 		snprint(cmpbuf, sizeof cmpbuf, "%T %s %s",
	+ 			lt, cmps[relindex(n->op)], xbuf);
	+ 	warn(n, "useless or misleading comparison: %s", cmpbuf);
	+ 	return 0;
	+ }
	+ 
 [rsc] --rw-rw-r-- M 84741 glenda sys 23923 Dec 11 12:22 sys/src/cmd/cc/lex.c
	/n/sourcesdump/2005/1211/plan9/sys/src/cmd/cc/lex.c:395,401 - 
	/n/sourcesdump/2005/1212/plan9/sys/src/cmd/cc/lex.c:395,401
	  yylex(void)
	  {
	  	vlong vv;
	- 	long c, c1;
	+ 	long c, c1, t;
	  	char *cp;
	  	Rune rune;
	  	Sym *s;
	/n/sourcesdump/2005/1211/plan9/sys/src/cmd/cc/lex.c:540,547 - 
	/n/sourcesdump/2005/1212/plan9/sys/src/cmd/cc/lex.c:540,549
	  		if(yylval.vval != vv)
	  			yyerror("overflow in character constant: 0x%lx", c);
	  		else
	- 		if(c & 0x80)
	+ 		if(c & 0x80){
	+ 			nearln = lineno;
	  			warn(Z, "sign-extended character constant");
	+ 		}
	  		yylval.vval = convvtox(vv, TCHAR);
	  		return LCONST;
	  
	/n/sourcesdump/2005/1211/plan9/sys/src/cmd/cc/lex.c:784,828 - 
	/n/sourcesdump/2005/1212/plan9/sys/src/cmd/cc/lex.c:786,827
	  	if(mpatov(symb, &yylval.vval))
	  		yyerror("overflow in constant");
	  
	+ 	vv = yylval.vval;
	  	if(c1 & Numvlong) {
	- 		if(c1 & Numuns) {
	+ 		if((c1 & Numuns) || convvtox(vv, TVLONG) < 0) {
	  			c = LUVLCONST;
	+ 			t = TUVLONG;
	  			goto nret;
	  		}
	- 		yylval.vval = convvtox(yylval.vval, TVLONG);
	- 		if(yylval.vval < 0) {
	- 			c = LUVLCONST;
	- 			goto nret;
	- 		}
	  		c = LVLCONST;
	+ 		t = TVLONG;
	  		goto nret;
	  	}
	  	if(c1 & Numlong) {
	- 		if(c1 & Numuns) {
	+ 		if((c1 & Numuns) || convvtox(vv, TLONG) < 0) {
	  			c = LULCONST;
	+ 			t = TULONG;
	  			goto nret;
	  		}
	- 		yylval.vval = convvtox(yylval.vval, TLONG);
	- 		if(yylval.vval < 0) {
	- 			c = LULCONST;
	- 			goto nret;
	- 		}
	  		c = LLCONST;
	+ 		t = TLONG;
	  		goto nret;
	  	}
	- 	if(c1 & Numuns) {
	+ 	if((c1 & Numuns) || convvtox(vv, TINT) < 0) {
	  		c = LUCONST;
	+ 		t = TUINT;
	  		goto nret;
	  	}
	- 	yylval.vval = convvtox(yylval.vval, TINT);
	- 	if(yylval.vval < 0) {
	- 		c = LUCONST;
	- 		goto nret;
	- 	}
	  	c = LCONST;
	+ 	t = TINT;
	  	goto nret;
	  
	  nret:
	+ 	yylval.vval = convvtox(vv, t);
	+ 	if(yylval.vval != vv){
	+ 		nearln = lineno;
	+ 		warn(Z, "truncated constant: %T %s", types[t], symb);
	+ 	}
	  	return c;
	  
	  casedot:
 [rsc] --rw-rw-r-- M 84741 jmk sys 8645 Dec 11 12:22 sys/src/cmd/cc/scon.c
	/n/sourcesdump/2005/1211/plan9/sys/src/cmd/cc/scon.c:226,231 - 
	/n/sourcesdump/2005/1212/plan9/sys/src/cmd/cc/scon.c:226,232
	  	} else {
	  		n->vconst = convvtox(v, n->type->etype);
	  	}
	+ 	n->oldop = n->op;
	  	n->op = OCONST;
	  }
	  
	/n/sourcesdump/2005/1211/plan9/sys/src/cmd/cc/scon.c:375,380 - 
	/n/sourcesdump/2005/1212/plan9/sys/src/cmd/cc/scon.c:376,382
	  	}
	  	c1 = trm[0].mult;
	  	if(j == 0) {
	+ 		n->oldop = n->op;
	  		n->op = OCONST;
	  		n->vconst = c1;
	  		return;
 [rsc] --rw-rw-r-- M 84741 glenda sys 34315 Dec 11 12:22 sys/src/cmd/cc/sub.c
	/n/sourcesdump/2005/1211/plan9/sys/src/cmd/cc/sub.c:1484,1489 - 
	/n/sourcesdump/2005/1212/plan9/sys/src/cmd/cc/sub.c:1484,1490
	  	-1,		0,	0,
	  };
	  
	+ /*	OEQ, ONE, OLE, OLS, OLT, OLO, OGE, OHS, OGT, OHI */
	  char	comrel[12] =
	  {
	  	ONE, OEQ, OGT, OHI, OGE, OHS, OLT, OLO, OLE, OLS,
	/n/sourcesdump/2005/1211/plan9/sys/src/cmd/cc/sub.c:1522,1527 - 
	/n/sourcesdump/2005/1212/plan9/sys/src/cmd/cc/sub.c:1523,1529
	  
	  char	typechl[NTYPE];
	  char	typechlv[NTYPE];
	+ char typechlvp[NTYPE];
	  int	typechlinit[] =
	  {
	  	TCHAR, TUCHAR, TSHORT, TUSHORT, TINT, TUINT, TLONG, TULONG, -1,
	/n/sourcesdump/2005/1211/plan9/sys/src/cmd/cc/sub.c:1868,1877 - 
	/n/sourcesdump/2005/1212/plan9/sys/src/cmd/cc/sub.c:1870,1881
	  		urk("typechl", nelem(typechl), typechlinit[i]);
	  		typechl[typechlinit[i]] = 1;
	  		typechlv[typechlinit[i]] = 1;
	+ 		typechlvp[typechlinit[i]] = 1;
	  	}
	  	for(i=0; typechlpinit[i] >= 0; i++) {
	  		urk("typechlp", nelem(typechlp), typechlpinit[i]);
	  		typechlp[typechlpinit[i]] = 1;
	+ 		typechlvp[typechlinit[i]] = 1;
	  	}
	  	for(i=0; typechlpfdinit[i] >= 0; i++) {
	  		urk("typechlpfd", nelem(typechlpfd), typechlpfdinit[i]);
	/n/sourcesdump/2005/1211/plan9/sys/src/cmd/cc/sub.c:1893,1898 - 
	/n/sourcesdump/2005/1212/plan9/sys/src/cmd/cc/sub.c:1897,1903
	  		urk("typev", nelem(typev), typevinit[i]);
	  		typev[typevinit[i]] = 1;
	  		typechlv[typevinit[i]] = 1;
	+ 		typechlvp[typechlinit[i]] = 1;
	  	}
	  	for(i=0; typefdinit[i] >= 0; i++) {
	  		urk("typefd", nelem(typefd), typefdinit[i]);