SvGETMAGIC: evaluate its argument just once

This required making it into an inline function.  I tried using
STMT_START{ ... } STMT_END, which should work since it has a void
return, but there were places where it was used in a comma operator, and
those did not compile.

1 files changed, 19 insertions, 0 deletions

diff --git a/sv_inline.h b/sv_inline.h
index c495d3cea0..2c2eff27df 100644
--- a/sv_inline.h
+++ b/sv_inline.h
@@ -565,6 +565,25 @@ Perl_SvPVXtrue(pTHX_ SV *sv)
     return *sv->sv_u.svu_pv != '0';
 }
 
+/*
+=for apidoc SvGETMAGIC
+Invokes C<L</mg_get>> on an SV if it has 'get' magic.  For example, this
+will call C<FETCH> on a tied variable.  As of 5.37.1, this function is
+guaranteed to evaluate its argument exactly once.
+
+=cut
+*/
+
+PERL_STATIC_INLINE void
+Perl_SvGETMAGIC(pTHX_ SV *sv)
+{
+    PERL_ARGS_ASSERT_SVGETMAGIC;
+
+    if (UNLIKELY(SvGMAGICAL(sv))) {
+        mg_get(sv);
+    }
+}
+
 PERL_STATIC_INLINE bool
 Perl_SvTRUE(pTHX_ SV *sv)
 {