Stop constant inlining from countermanding ‘use subs’

Ever since

commit f7461760003db2ce68155c97ea6c1658e96fcd27
Author: Zefram <zefram@fysh.org>
Date:   Sun Nov 8 15:03:45 2009 +0100

    Bareword sub lookups
    ...

this has failed:

$ perl5.10 -le 'use subs "abs";  sub abs() {44}; print abs + abs'
88
$ perl5.12 -le 'use subs "abs";  sub abs() {44}; print abs + abs'
44

A GV holding a single constant is a candidate for downgrading after
it uhas been used.  The GV gets downgraded after the first ‘abs’ is
inlined.  In the process, the CV-imported flag, which is stored in the
GV, not the CV, is lost, preventing &abs from overriding the built-in
function on the second mention.

There is a special flag for RVs, namely SVprv_PCS_IMPORTED,
which indicates that, when expanded to GVs, they should have the
GVf_IMPORTED_CV flag set.  But gv_try_downgrade wasn‘t setting
that flag.

1 files changed, 2 insertions, 1 deletions

diff --git a/gv.c b/gv.c
index 23251940a3..b89181e061 100644
--- a/gv.c
+++ b/gv.c
@@ -3174,10 +3174,11 @@ Perl_gv_try_downgrade(pTHX_ GV *gv)
 			HEK_LEN(namehek)*(HEK_UTF8(namehek) ? -1 : 1), 0)) &&
 	    *gvp == (SV*)gv) {
 	SV *value = SvREFCNT_inc(CvXSUBANY(cv).any_ptr);
+	const bool imported = !!GvIMPORTED_CV(gv);
 	SvREFCNT(gv) = 0;
 	sv_clear((SV*)gv);
 	SvREFCNT(gv) = 1;
-	SvFLAGS(gv) = SVt_IV|SVf_ROK;
+	SvFLAGS(gv) = SVt_IV|SVf_ROK|SVprv_PCS_IMPORTED * imported;
 	SvANY(gv) = (XPVGV*)((char*)&(gv->sv_u.svu_iv) -
 				STRUCT_OFFSET(XPVIV, xiv_iv));
 	SvRV_set(gv, value);