op.c: don't warn about !!$x == $y

Exempt `!!` from the "Possible precedence problem between ! and <cmp>"
warning.

Fixes #22954.

op.c

@@ -12302,6 +12302,10 @@ check_precedence_not_vs_cmp(pTHX_ const OP *const o)
             && right->op_type == OP_CONST
             && SvIsBOOL(cSVOPx_sv(right))
         )
+        && (                                /* ... nor  !!$x == ...      */
+            (cUNOPx(left)->op_first->op_flags & OPf_PARENS)
+            || cUNOPx(left)->op_first->op_type != OP_NOT
+        )
     ) {
         Perl_ck_warner(aTHX_ packWARN(WARN_PRECEDENCE),
             "Possible precedence problem between ! and %s", OP_DESC(o)

pod/perldelta.pod

@@ -230,6 +230,14 @@ XXX Changes (i.e. rewording) of diagnostic messages go here
 
 =item *
 
+L<Possible precedence problem between ! and %s|perldiag/"Possible precedence problem between ! and %s">
+
+This warning no longer triggers for code like C<!!$x == $y>, i.e. where double
+negation (C<!!>) is used as a convert-to-boolean operator.
+[GH #22954]
+
+=item *
+
 XXX Describe change here
 
 =back

t/lib/warnings/op

@@ -1590,6 +1590,8 @@ for my $op (qw( == != < > <= >= eq ne lt gt le ge )) {
     $code .= "\$a = !\$a $op \$b;\n";  # should warn
     $code .= "\$a = (!\$a) $op \$b;\n";
     $code .= "\$a = !(\$a) $op \$b;\n";  # should warn
+    $code .= "\$a = !!\$a $op \$b;\n";
+    $code .= "\$a = !(!\$a) $op \$b;\n";  # should warn
     $code .= "\$a = !(\$a $op \$b);\n";
     $code .= "\$a = !\$a $op !0;\n";
     $code .= "\$a = !\$a $op !A_CONSTANT;\n";
@@ -1623,28 +1625,40 @@ Possible precedence problem between ! and derived class test at - line 6.
 Possible precedence problem between ! and derived class test at - line 8.
 Possible precedence problem between ! and numeric eq (==) at [cmp] line 1.
 Possible precedence problem between ! and numeric eq (==) at [cmp] line 3.
-Possible precedence problem between ! and numeric ne (!=) at [cmp] line 8.
+Possible precedence problem between ! and numeric eq (==) at [cmp] line 5.
 Possible precedence problem between ! and numeric ne (!=) at [cmp] line 10.
-Possible precedence problem between ! and numeric lt (<) at [cmp] line 15.
-Possible precedence problem between ! and numeric lt (<) at [cmp] line 17.
-Possible precedence problem between ! and numeric gt (>) at [cmp] line 22.
-Possible precedence problem between ! and numeric gt (>) at [cmp] line 24.
-Possible precedence problem between ! and numeric le (<=) at [cmp] line 29.
-Possible precedence problem between ! and numeric le (<=) at [cmp] line 31.
-Possible precedence problem between ! and numeric ge (>=) at [cmp] line 36.
-Possible precedence problem between ! and numeric ge (>=) at [cmp] line 38.
-Possible precedence problem between ! and string eq at [cmp] line 43.
-Possible precedence problem between ! and string eq at [cmp] line 45.
-Possible precedence problem between ! and string ne at [cmp] line 50.
-Possible precedence problem between ! and string ne at [cmp] line 52.
-Possible precedence problem between ! and string lt at [cmp] line 57.
-Possible precedence problem between ! and string lt at [cmp] line 59.
-Possible precedence problem between ! and string gt at [cmp] line 64.
-Possible precedence problem between ! and string gt at [cmp] line 66.
-Possible precedence problem between ! and string le at [cmp] line 71.
-Possible precedence problem between ! and string le at [cmp] line 73.
-Possible precedence problem between ! and string ge at [cmp] line 78.
-Possible precedence problem between ! and string ge at [cmp] line 80.
+Possible precedence problem between ! and numeric ne (!=) at [cmp] line 12.
+Possible precedence problem between ! and numeric ne (!=) at [cmp] line 14.
+Possible precedence problem between ! and numeric lt (<) at [cmp] line 19.
+Possible precedence problem between ! and numeric lt (<) at [cmp] line 21.
+Possible precedence problem between ! and numeric lt (<) at [cmp] line 23.
+Possible precedence problem between ! and numeric gt (>) at [cmp] line 28.
+Possible precedence problem between ! and numeric gt (>) at [cmp] line 30.
+Possible precedence problem between ! and numeric gt (>) at [cmp] line 32.
+Possible precedence problem between ! and numeric le (<=) at [cmp] line 37.
+Possible precedence problem between ! and numeric le (<=) at [cmp] line 39.
+Possible precedence problem between ! and numeric le (<=) at [cmp] line 41.
+Possible precedence problem between ! and numeric ge (>=) at [cmp] line 46.
+Possible precedence problem between ! and numeric ge (>=) at [cmp] line 48.
+Possible precedence problem between ! and numeric ge (>=) at [cmp] line 50.
+Possible precedence problem between ! and string eq at [cmp] line 55.
+Possible precedence problem between ! and string eq at [cmp] line 57.
+Possible precedence problem between ! and string eq at [cmp] line 59.
+Possible precedence problem between ! and string ne at [cmp] line 64.
+Possible precedence problem between ! and string ne at [cmp] line 66.
+Possible precedence problem between ! and string ne at [cmp] line 68.
+Possible precedence problem between ! and string lt at [cmp] line 73.
+Possible precedence problem between ! and string lt at [cmp] line 75.
+Possible precedence problem between ! and string lt at [cmp] line 77.
+Possible precedence problem between ! and string gt at [cmp] line 82.
+Possible precedence problem between ! and string gt at [cmp] line 84.
+Possible precedence problem between ! and string gt at [cmp] line 86.
+Possible precedence problem between ! and string le at [cmp] line 91.
+Possible precedence problem between ! and string le at [cmp] line 93.
+Possible precedence problem between ! and string le at [cmp] line 95.
+Possible precedence problem between ! and string ge at [cmp] line 100.
+Possible precedence problem between ! and string ge at [cmp] line 102.
+Possible precedence problem between ! and string ge at [cmp] line 104.
 Possible precedence problem between ! and pattern match (m//) at [bind] line 1.
 Possible precedence problem between ! and pattern match (m//) at [bind] line 3.
 Possible precedence problem between ! and pattern match (m//) at [bind] line 6.