hv.* - disable unshared keys except when requested

This disables the new unshared hash key logic by default. People
who wish to try it out can enable it at build time with

    -DPERL_USE_UNSHARED_KEYS_IN_LARGE_HASHES

in the configure process.

3 files changed, 18 insertions, 2 deletions

diff --git a/hv.c b/hv.c
index d4325bcd77..5e19941179 100644
--- a/hv.c
+++ b/hv.c
@@ -1576,7 +1576,12 @@ S_hv_delete_common(pTHX_ HV *hv, SV *keysv, const char *key, STRLEN klen,
 
    This is a heuristic. There might be a better answer than 42, but for now
    we'll use it.
+
+   NOTE: Configure with -Accflags='-DPERL_USE_UNSHARED_KEYS_IN_LARGE_HASHES'
+   to enable this new functionality.
 */
+
+#ifdef PERL_USE_UNSHARED_KEYS_IN_LARGE_HASHES
 static bool
 S_large_hash_heuristic(pTHX_ HV *hv, STRLEN size) {
     if (size > 42
@@ -1588,6 +1593,7 @@ S_large_hash_heuristic(pTHX_ HV *hv, STRLEN size) {
     }
     return FALSE;
 }
+#endif
 
 STATIC void
 S_hsplit(pTHX_ HV *hv, STRLEN const oldsize, STRLEN newsize)
@@ -1624,7 +1630,7 @@ S_hsplit(pTHX_ HV *hv, STRLEN const oldsize, STRLEN newsize)
         return;
 
     /* don't share keys in large simple hashes */
-    if (S_large_hash_heuristic(aTHX_ hv, HvTOTALKEYS(hv)))
+    if (LARGE_HASH_HEURISTIC(hv, HvTOTALKEYS(hv)))
         HvSHAREKEYS_off(hv);
 
 
@@ -1720,7 +1726,7 @@ Perl_hv_ksplit(pTHX_ HV *hv, IV newmax)
         }
 #endif
     } else {
-        if (S_large_hash_heuristic(aTHX_ hv, newmax))
+        if (LARGE_HASH_HEURISTIC(hv, newmax))
             HvSHAREKEYS_off(hv);
         Newxz(a, PERL_HV_ARRAY_ALLOC_BYTES(newsize), char);
         xhv->xhv_max = newsize - 1;
diff --git a/hv.h b/hv.h
index bd81e5750c..2c5e796d9b 100644
--- a/hv.h
+++ b/hv.h
@@ -28,6 +28,13 @@
 #   define PERL_HASH_ITER_BUCKET(iter)      (((iter)->xhv_riter) ^ ((iter)->xhv_rand))
 #endif
 
+#ifdef PERL_USE_UNSHARED_KEYS_IN_LARGE_HASHES
+#define LARGE_HASH_HEURISTIC(hv,new_max) S_large_hash_heuristic(aTHX_ (hv), (new_max))
+#else
+#define LARGE_HASH_HEURISTIC(hv,new_max) 0
+#endif
+
+
 /* entry in hash value chain */
 struct he {
     /* Keep hent_next first in this structure, because sv_free_arenas take
diff --git a/perl.c b/perl.c
index 486048aa68..057cd0e99a 100644
--- a/perl.c
+++ b/perl.c
@@ -1958,6 +1958,9 @@ S_Internals_V(pTHX_ CV *cv)
 #  ifdef PERL_USE_SAFE_PUTENV
                              " PERL_USE_SAFE_PUTENV"
 #  endif
+#  ifdef PERL_USE_UNSHARED_KEYS_IN_LARGE_HASHES
+                             " PERL_USE_UNSHARED_KEYS_IN_LARGE_HASHES"
+#  endif
 #  ifdef SILENT_NO_TAINT_SUPPORT
                              " SILENT_NO_TAINT_SUPPORT"
 #  endif