Perl_do_print: use S_uiv_2buf for faster IV stringification

`Perl_do_print`'s pre-existing method for stringification of an IV within
an SVt_IV involves creating a temporary SVt_PV, using `sv_vcatpvfn_flags`
to do the stringification, then freeing the SVt_PV once the buffer has
been written out.

This is considerably slower than using `S_uiv_2buf`, the helper
function used by `sv_2pv_flags`. So this commit modifies `Perl_do_print`
to use `sv_2pv_flags`.

Author: richardleach

doio.c

@@ -2205,11 +2205,25 @@ Perl_do_print(pTHX_ SV *sv, PerlIO *fp)
         return TRUE;
     if (SvTYPE(sv) == SVt_IV && SvIOK(sv)) {
         assert(!SvGMAGICAL(sv));
-        if (SvIsUV(sv))
-            PerlIO_printf(fp, "%" UVuf, (UV)SvUVX(sv));
-        else
-            PerlIO_printf(fp, "%" IVdf, (IV)SvIVX(sv));
-        return !PerlIO_error(fp);
+        bool happy = TRUE;
+
+        /* Adapted from Perl_sv_2pv_flags */
+        const U32 isUIOK = SvIsUV(sv);
+        /* The purpose of this union is to ensure that arr is aligned on
+           a 2 byte boundary, because that is what uiv_2buf() requires */
+        union {
+            char arr[TYPE_CHARS(UV)];
+            U16 dummy;
+        } buf;
+        char *ebuf, *ptr;
+        STRLEN len;
+        UV tempuv = SvUVX(sv);
+        ptr = uiv_2buf(buf.arr, SvIVX(sv), tempuv, isUIOK, &ebuf);
+        len = ebuf - ptr;
+
+        if (len && (PerlIO_write(fp,ptr,len) == 0))
+            happy = FALSE;
+        return happy ? !PerlIO_error(fp) : FALSE;
     }
     else {
         STRLEN len;

t/perf/benchmarks

@@ -1938,6 +1938,18 @@
         code    => '$p = pos($s);',
     },
 
+    # func::print::iv_stringify should outperform func::print::iv_strings
+    'func::print::iv_stringify' => {
+        desc    => 'do_print stringification of SVt_IV integers',
+        setup   => 'open(my $devnull, ">>", "/dev/null") or die $!;',
+        code    => 'print $devnull 1,2,3,4,5,6,7,8,9,0;',
+    },
+    'func::print::iv_strings' => {
+        desc    => 'do_print pre-stringified SVt_IV integers',
+        setup   => 'open(my $devnull, ">>", "/dev/null") or die $!;',
+        code    => 'print $devnull "1","2","3","4","5","6","7","8","9","0";',
+    },
+
     'func::ref::notaref_bool' => {
         desc    => 'ref($notaref) in boolean context',
         setup   => 'my $r = "boo"',
@@ -1970,8 +1982,6 @@
         code    => '$x = ref $r',
     },
 
-
-
     'func::sort::num' => {
         desc    => 'plain numeric sort',
         setup   => 'my (@a, @b); @a = reverse 1..10;',
@@ -2034,7 +2044,6 @@
         code    => '@a = sort f @a',
     },
 
-
     'func::split::vars' => {
         desc    => 'split into two lexical vars',
         setup   => 'my $s = "abc:def";',