libc qsort(3): stop aliasing.

Qsort swap code aliases the sorted array elements to ints and longs in
order to do swap by machine words.  Unfortunately this breaks with the
full code optimization, e.g. LTO.

See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83201 which seems to
reference code directly copied from libc/stdlib/qsort.c.

PR:	228780
Reported by:	mliska@suse.cz
Reviewed by:	brooks
Sponsored by:	The FreeBSD Foundation
MFC after:	2 weeks
Differential revision:	https://reviews.freebsd.org/D15714

lib/libc/stdlib/qsort.c

@@ -43,53 +43,27 @@ typedef int		 cmp_t(void *, const void *, const void *);
 typedef int		 cmp_t(const void *, const void *);
 #endif
 static inline char	*med3(char *, char *, char *, cmp_t *, void *);
-static inline void	 swapfunc(char *, char *, size_t, int, int);
 
 #define	MIN(a, b)	((a) < (b) ? a : b)
 
 /*
  * Qsort routine from Bentley & McIlroy's "Engineering a Sort Function".
  */
-#define	swapcode(TYPE, parmi, parmj, n) {		\
-	size_t i = (n) / sizeof (TYPE);			\
-	TYPE *pi = (TYPE *) (parmi);		\
-	TYPE *pj = (TYPE *) (parmj);		\
-	do { 						\
-		TYPE	t = *pi;		\
-		*pi++ = *pj;				\
-		*pj++ = t;				\
-	} while (--i > 0);				\
-}
-
-#define	SWAPINIT(TYPE, a, es) swaptype_ ## TYPE =	\
-	((char *)a - (char *)0) % sizeof(TYPE) ||	\
-	es % sizeof(TYPE) ? 2 : es == sizeof(TYPE) ? 0 : 1;
 
 static inline void
-swapfunc(char *a, char *b, size_t n, int swaptype_long, int swaptype_int)
+swapfunc(char *a, char *b, size_t es)
 {
-	if (swaptype_long <= 1)
-		swapcode(long, a, b, n)
-	else if (swaptype_int <= 1)
-		swapcode(int, a, b, n)
-	else
-		swapcode(char, a, b, n)
-}
+	char t;
 
-#define	swap(a, b)					\
-	if (swaptype_long == 0) {			\
-		long t = *(long *)(a);			\
-		*(long *)(a) = *(long *)(b);		\
-		*(long *)(b) = t;			\
-	} else if (swaptype_int == 0) {			\
-		int t = *(int *)(a);			\
-		*(int *)(a) = *(int *)(b);		\
-		*(int *)(b) = t;			\
-	} else						\
-		swapfunc(a, b, es, swaptype_long, swaptype_int)
+	do {
+		t = *a;
+		*a++ = *b;
+		*b++ = t;
+	} while (--es > 0);
+}
 
 #define	vecswap(a, b, n)				\
-	if ((n) > 0) swapfunc(a, b, n, swaptype_long, swaptype_int)
+	if ((n) > 0) swapfunc(a, b, n)
 
 #ifdef I_AM_QSORT_R
 #define	CMP(t, x, y) (cmp((t), (x), (y)))
@@ -121,17 +95,16 @@ qsort(void *a, size_t n, size_t es, cmp_t *cmp)
 	char *pa, *pb, *pc, *pd, *pl, *pm, *pn;
 	size_t d1, d2;
 	int cmp_result;
-	int swaptype_long, swaptype_int, swap_cnt;
+	int swap_cnt;
 
-loop:	SWAPINIT(long, a, es);
-	SWAPINIT(int, a, es);
+loop:
 	swap_cnt = 0;
 	if (n < 7) {
 		for (pm = (char *)a + es; pm < (char *)a + n * es; pm += es)
 			for (pl = pm; 
 			     pl > (char *)a && CMP(thunk, pl - es, pl) > 0;
 			     pl -= es)
-				swap(pl, pl - es);
+				swapfunc(pl, pl - es, es);
 		return;
 	}
 	pm = (char *)a + (n / 2) * es;
@@ -147,30 +120,30 @@ loop:	SWAPINIT(long, a, es);
 		}
 		pm = med3(pl, pm, pn, cmp, thunk);
 	}
-	swap(a, pm);
+	swapfunc(a, pm, es);
 	pa = pb = (char *)a + es;
 
 	pc = pd = (char *)a + (n - 1) * es;
 	for (;;) {
 		while (pb <= pc && (cmp_result = CMP(thunk, pb, a)) <= 0) {
 			if (cmp_result == 0) {
 				swap_cnt = 1;
-				swap(pa, pb);
+				swapfunc(pa, pb, es);
 				pa += es;
 			}
 			pb += es;
 		}
 		while (pb <= pc && (cmp_result = CMP(thunk, pc, a)) >= 0) {
 			if (cmp_result == 0) {
 				swap_cnt = 1;
-				swap(pc, pd);
+				swapfunc(pc, pd, es);
 				pd -= es;
 			}
 			pc -= es;
 		}
 		if (pb > pc)
 			break;
-		swap(pb, pc);
+		swapfunc(pb, pc, es);
 		swap_cnt = 1;
 		pb += es;
 		pc -= es;
@@ -180,7 +153,7 @@ loop:	SWAPINIT(long, a, es);
 			for (pl = pm; 
 			     pl > (char *)a && CMP(thunk, pl - es, pl) > 0;
 			     pl -= es)
-				swap(pl, pl - es);
+				swapfunc(pl, pl - es, es);
 		return;
 	}