op.c: Stop copying constants under ithreads

This fixes bugs #21979, #89188, #109746, #114838 and #115388 and
mostly fixes #109744 and #105906 (other issues still remain in those
two tickets).

Because the PADTMP flag was doing double duty, indicating that a
pad slot was in use in addition to indicating a target, constants
could not be shared between pad slots, as freeing one const op (and
turning of its PADTMP flag in pad_free) would mark some other pad
slot as free.

I believe this may have been fixed already by change 3b1c21fabed,
which made const ops use pad_swipe (which removes the SV from the
pad) instead of pad_free (which marks it as available for reuse).  But
the copying still happens.

In any case, as of the previous commit, whether a pad slot for a con-
stant is in use is now stored in the pad name.  Slots in use for const
ops now have &PL_sv_no names.

So there is no longer any reason to copy the constants.

The difference can be observed thus:

Before:

$ ./perl -lIlib -MDevel::Peek -e 'sub foo(){42} Dump foo; Dump foo'
SV = IV(0x7f94ea02ef10) at 0x7f94ea02ef20
  REFCNT = 2
  FLAGS = (PADTMP,IOK,READONLY,pIOK)
  IV = 42
SV = IV(0x7f94ea02eeb0) at 0x7f94ea02eec0
  REFCNT = 1
  FLAGS = (PADTMP,IOK,READONLY,pIOK)
  IV = 42

After:

$ ./perl -lIlib -MDevel::Peek -e 'sub foo(){42} Dump foo; Dump foo'
SV = IV(0x7f894882ef10) at 0x7f894882ef20
  REFCNT = 3
  FLAGS = (IOK,READONLY,pIOK)
  IV = 42
SV = IV(0x7f894882ef10) at 0x7f894882ef20
  REFCNT = 3
  FLAGS = (IOK,READONLY,pIOK)
  IV = 42

Notice the different addresses.

There are still special cases for copying &PL_sv_undef, which I need
to tackle.

Since most constants created by ‘use constant’ have the PADMY flag on
(since they reside in lexical variables inside constant.pm) and PADMY
and PADTMP are exclusive, I have stop turning on PADTMP for constants.
It is no longer necessary now, since before its purpose was to mark
pad entries as being in use.  That means many to-do tests pass.

2 files changed, 16 insertions, 5 deletions

diff --git a/ext/B/t/OptreeCheck.pm b/ext/B/t/OptreeCheck.pm
index 45523133a3..547f017d72 100644
--- a/ext/B/t/OptreeCheck.pm
+++ b/ext/B/t/OptreeCheck.pm
@@ -213,7 +213,8 @@ They're both required, and the correct one is selected for the platform
 being tested, and saved into the synthesized property B<wanted>.
 
 Individual sample lines may be suffixed with whitespace followed
-by (<|<=|==|>=|>)5.nnnn to select that line only for the listed perl
+by (<|<=|==|>=|>)5.nnnn (up to two times) to
+select that line only for the listed perl
 version; the whitespace and conditional are stripped.
 
 =head2 bcopts => $bcopts || [ @bcopts ]
@@ -641,9 +642,10 @@ sub mkCheckRex {
 
     # strip out conditional lines
 
-    $str =~ s{^(.*?)\s+(<|<=|==|>=|>)\s*(5\.\d+)\ *\n}
+    $str =~ s{^(.*?)   \s+(<|<=|==|>=|>)\s*(5\.\d+)
+		    (?:\s+(<|<=|==|>=|>)\s*(5\.\d+))? \ *\n}
      {
-	my ($line, $cmp, $version) = ($1,$2,$3);
+	my ($line, $cmp, $version, $cmp2, $v2) = ($1,$2,$3,$4,$5,$6);
 	my $repl = "";
 	if (  $cmp eq '<'  ? $] <  $version
 	    : $cmp eq '<=' ? $] <= $version
@@ -651,11 +653,19 @@ sub mkCheckRex {
 	    : $cmp eq '>=' ? $] >= $version
 	    : $cmp eq '>'  ? $] >  $version
 	    : die("bad comparision '$cmp' in string [$str]\n")
+	 and !$cmp2 || (
+	      $cmp2 eq '<'  ? $] <  $v2
+	    : $cmp2 eq '<=' ? $] <= $v2
+	    : $cmp2 eq '==' ? $] == $v2
+	    : $cmp2 eq '>=' ? $] >= $v2
+	    : $cmp2 eq '>'  ? $] >  $v2
+	    : die("bad comparision '$cmp2' in string [$str]\n")
+	  )
 	) {
 	    $repl = "$line\n";
 	}
 	$repl;
-     }gem;
+     }gemx;
 
     $tc->{wantstr} = $str;
 
diff --git a/ext/B/t/optree_constants.t b/ext/B/t/optree_constants.t
index bfd355e0cc..d08c6be93d 100644
--- a/ext/B/t/optree_constants.t
+++ b/ext/B/t/optree_constants.t
@@ -348,7 +348,8 @@ checkOptree ( name	=> 'lc*,uc*,gt,lt,ge,le,cmp',
 # n           <$> const[PV "b-cmp-a"] s ->o
 # p        <;> nextstate(main 916 optree_constants.t:313) v:>,<,%,{ ->q
 # q        <$> const[PVNV 0] s/SHORT ->r      < 5.017002
-# q        <$> const[PVNV 0] s/FOLD,SHORT ->r >=5.017002
+# q        <$> const[PVNV 0] s/FOLD,SHORT ->r >=5.017002 < 5.019001
+# q        <$> const[SPECIAL sv_no] s/FOLD,SHORT ->r >=5.019001
 EOT_EOT
 # r  <1> leavesub[1 ref] K/REFC,1 ->(end)
 # -     <@> lineseq KP ->r