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[PATCH 1/2] Introduce gcc_sort_r


Hi,

this patch adds gcc_sort_r, a function similar to Glibc qsort_r that takes an
extra 'user data' pointer and passes it to comparators.  Richi asked about it
in https://gcc.gnu.org/ml/gcc-patches/2019-07/msg01383.html , see followups in
that thread for other approaches that were considered.

Patch 2/2, unchanged from Richard's version, uses the new function in domwalk.

Bootstrapped/regtested on x86-64.

Thanks.
Alexander

	* sort.cc (sort_r_ctx): New struct.
	(reorder23): Make templated on context type.
	(reorder45): Ditto.
	(cmp1): Ditto.  Adjust signature.
	(netsort): Ditto.
	(mergesort): Ditto.
	[CHECKING_P] (cmp2to3): New static function.  Use it...
	(gcc_qsort) [CHECKING_P]: ...here.
	(gcc_sort_r): New function.
	* system.h (sort_r_cmp_fn): New function typedef.
	(qsort_chk): Adjust signature.
	(gcc_sort_r): Declare.
	* vec.c (qsort_chk_error): Adjust.
	(qsort_chk): Adjust.
	
diff --git a/gcc/sort.cc b/gcc/sort.cc
index 3e9c032c462..73a9f7ed7c5 100644
--- a/gcc/sort.cc
+++ b/gcc/sort.cc
@@ -58,8 +58,25 @@ struct sort_ctx
   size_t nlim; // limit for network sort
 };
 
+/* Like sort_ctx, but for use with qsort_r-style comparators.  Several
+   functions in this file are templates that work with either context type.  */
+struct sort_r_ctx
+{
+  void          *data;
+  sort_r_cmp_fn *cmp_;
+  char   *out;
+  size_t n;
+  size_t size;
+  size_t nlim;
+  int cmp (const void *a, const void *b)
+  {
+    return cmp_ (a, b, data);
+  }
+};
+
 /* Helper for netsort. Permute, possibly in-place, 2 or 3 elements,
    placing E0 to C->OUT, E1 to C->OUT + C->SIZE, and so on.  */
+template<typename sort_ctx>
 static void
 reorder23 (sort_ctx *c, char *e0, char *e1, char *e2)
 {
@@ -90,6 +107,7 @@ do {                                                     \
 }
 
 /* Like reorder23, but permute 4 or 5 elements.  */
+template<typename sort_ctx>
 static void
 reorder45 (sort_ctx *c, char *e0, char *e1, char *e2, char *e3, char *e4)
 {
@@ -127,21 +145,23 @@ do {                                                     \
    Return E0^E1 if E0 compares less than E1, zero otherwise.
    This is noinline to avoid code growth and confine invocation
    to a single call site, assisting indirect branch prediction.  */
+template<typename sort_ctx>
 noinline static intptr_t
-cmp1 (char *e0, char *e1, cmp_fn *cmp)
+cmp1 (char *e0, char *e1, sort_ctx *c)
 {
   intptr_t x = (intptr_t)e0 ^ (intptr_t)e1;
-  return x & (cmp (e0, e1) >> 31);
+  return x & (c->cmp (e0, e1) >> 31);
 }
 
 /* Execute network sort on 2 to 5 elements from IN, placing them into C->OUT.
    IN may be equal to C->OUT, in which case elements are sorted in place.  */
+template<typename sort_ctx>
 static void
 netsort (char *in, sort_ctx *c)
 {
 #define CMP(e0, e1)                   \
 do {                                  \
-  intptr_t x = cmp1 (e1, e0, c->cmp); \
+  intptr_t x = cmp1 (e1, e0, c);      \
   e0 = (char *)((intptr_t)e0 ^ x);    \
   e1 = (char *)((intptr_t)e1 ^ x);    \
 } while (0)
@@ -176,6 +196,7 @@ do {                                  \
 /* Execute merge sort on N elements from IN, placing them into OUT,
    using TMP as temporary storage if IN is equal to OUT.
    This is a stable sort if netsort is used only for 2 or 3 elements.  */
+template<typename sort_ctx>
 static void
 mergesort (char *in, sort_ctx *c, size_t n, char *out, char *tmp)
 {
@@ -217,6 +238,17 @@ do {                                            \
   memcpy (out, l, r - out);
 }
 
+#if CHECKING_P
+/* Adapter for using two-argument comparators in functions expecting the
+   three-argument sort_r_cmp_fn type.  */
+static int
+cmp2to3 (const void *a, const void *b, void *c)
+{
+  return ((cmp_fn *)c) (a, b);
+}
+#endif
+
+/* Replacement for C qsort.  */
 void
 gcc_qsort (void *vbase, size_t n, size_t size, cmp_fn *cmp)
 {
@@ -235,10 +267,30 @@ gcc_qsort (void *vbase, size_t n, size_t size, cmp_fn *cmp)
   if (buf != scratch)
     free (buf);
 #if CHECKING_P
-  qsort_chk (vbase, n, size, cmp);
+  qsort_chk (vbase, n, size, cmp2to3, (void*)cmp);
 #endif
 }
 
+/* Substitute for Glibc qsort_r.  */
+void
+gcc_sort_r (void *vbase, size_t n, size_t size, sort_r_cmp_fn *cmp, void *data)
+{
+  if (n < 2)
+    return;
+  char *base = (char *)vbase;
+  sort_r_ctx c = {data, cmp, base, n, size, 5};
+  long long scratch[32];
+  size_t bufsz = (n / 2) * size;
+  void *buf = bufsz <= sizeof scratch ? scratch : xmalloc (bufsz);
+  mergesort (base, &c, n, base, (char *)buf);
+  if (buf != scratch)
+    free (buf);
+#if CHECKING_P
+  qsort_chk (vbase, n, size, cmp, data);
+#endif
+}
+
+/* Stable sort, signature-compatible to C qsort.  */
 void
 gcc_stablesort (void *vbase, size_t n, size_t size, cmp_fn *cmp)
 {
diff --git a/gcc/system.h b/gcc/system.h
index d04f8fd3360..56af544b70b 100644
--- a/gcc/system.h
+++ b/gcc/system.h
@@ -1197,13 +1197,14 @@ helper_const_non_const_cast (const char *p)
 /* Get definitions of HOST_WIDE_INT.  */
 #include "hwint.h"
 
-/* GCC qsort API-compatible functions: except in release-checking compilers,
-   redirect 4-argument qsort calls to gcc_qsort; keep 1-argument invocations
-   corresponding to vec::qsort (cmp): they use C qsort internally anyway.  */
-void qsort_chk (void *, size_t, size_t, int (*)(const void *, const void *));
+typedef int sort_r_cmp_fn (const void *, const void *, void *);
+void qsort_chk (void *, size_t, size_t, sort_r_cmp_fn *, void *);
+void gcc_sort_r (void *, size_t, size_t, sort_r_cmp_fn *, void *);
 void gcc_qsort (void *, size_t, size_t, int (*)(const void *, const void *));
 void gcc_stablesort (void *, size_t, size_t,
 		     int (*)(const void *, const void *));
+/* Redirect four-argument qsort calls to gcc_qsort; one-argument invocations
+   correspond to vec::qsort, and use C qsort internally.  */
 #define PP_5th(a1, a2, a3, a4, a5, ...) a5
 #undef qsort
 #define qsort(...) PP_5th (__VA_ARGS__, gcc_qsort, 3, 2, qsort, 0) (__VA_ARGS__)
diff --git a/gcc/vec.c b/gcc/vec.c
index cbd2db010f9..bac5eb753a3 100644
--- a/gcc/vec.c
+++ b/gcc/vec.c
@@ -192,21 +192,23 @@ dump_vec_loc_statistics (void)
 ATTRIBUTE_NORETURN ATTRIBUTE_COLD
 static void
 qsort_chk_error (const void *p1, const void *p2, const void *p3,
-		 int (*cmp) (const void *, const void *))
+		 sort_r_cmp_fn *cmp, void *data)
 {
   if (!p3)
     {
-      int r1 = cmp (p1, p2), r2 = cmp (p2, p1);
-      error ("qsort comparator not anti-commutative: %d, %d", r1, r2);
+      int r1 = cmp (p1, p2, data), r2 = cmp (p2, p1, data);
+      error ("qsort comparator not anti-symmetric: %d, %d", r1, r2);
     }
   else if (p1 == p2)
     {
-      int r = cmp (p1, p3);
+      int r = cmp (p1, p3, data);
       error ("qsort comparator non-negative on sorted output: %d", r);
     }
   else
     {
-      int r1 = cmp (p1, p2), r2 = cmp (p2, p3), r3 = cmp (p1, p3);
+      int r1 = cmp (p1, p2, data);
+      int r2 = cmp (p2, p3, data);
+      int r3 = cmp (p1, p3, data);
       error ("qsort comparator not transitive: %d, %d, %d", r1, r2, r3);
     }
   internal_error ("qsort checking failed");
@@ -215,8 +217,7 @@ qsort_chk_error (const void *p1, const void *p2, const void *p3,
 /* Verify anti-symmetry and transitivity for comparator CMP on sorted array
    of N SIZE-sized elements pointed to by BASE.  */
 void
-qsort_chk (void *base, size_t n, size_t size,
-	   int (*cmp)(const void *, const void *))
+qsort_chk (void *base, size_t n, size_t size, sort_r_cmp_fn *cmp, void *data)
 {
 #if 0
 #define LIM(n) (n)
@@ -225,9 +226,9 @@ qsort_chk (void *base, size_t n, size_t size,
 #define LIM(n) ((n) <= 16 ? (n) : 12 + floor_log2 (n))
 #endif
 #define ELT(i) ((const char *) base + (i) * size)
-#define CMP(i, j) cmp (ELT (i), ELT (j))
-#define ERR2(i, j) qsort_chk_error (ELT (i), ELT (j), NULL, cmp)
-#define ERR3(i, j, k) qsort_chk_error (ELT (i), ELT (j), ELT (k), cmp)
+#define CMP(i, j) cmp (ELT (i), ELT (j), data)
+#define ERR2(i, j) qsort_chk_error (ELT (i), ELT (j), NULL, cmp, data)
+#define ERR3(i, j, k) qsort_chk_error (ELT (i), ELT (j), ELT (k), cmp, data)
   size_t i1, i2, i, j;
   /* This outer loop iterates over maximum spans [i1, i2) such that
      elements within each span compare equal to each other.  */


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