Local variable 'o' hides a parameter of the same name

LGTM static code analysis identified declaration of 'o' in a scope where
a variable of the same name had already been declared in an enclosing
scope.

Simply renaming the variable within the inner scope did not work
(extensive segfaults).  Tony Cook identified problem:  In inner scope we
were using macro cLISTOPo, which implicitly modifies 'o'.  Since
cLISTOPo is nothing more than macro cLISTOPx() with 'o' provided as the
argument, we can resolve the problem by using cLISTOPx() with a better
named variable -- in this case, 'child'.

Reference:  https://lgtm.com/projects/g/Perl/perl5/snapshot/9b2028e54156e4dbcc7a57bbd72e1b00a2e0ce39/files/op.c?sort=name&dir=ASC&mode=heatmap#x9b0ebeab3d026530:1

diff --git a/op.c b/op.c
index 7edee71..2d295a9 100644 (file)
--- a/op.c
+++ b/op.c
@@ -8047,28 +8047,28 @@ Perl_pmruntime(pTHX_ OP *o, OP *expr, OP *repl, UV flags, I32 floor)
      * also, mark any arrays as LIST/REF */
 
     if (expr->op_type == OP_LIST) {
-        OP *o;
-        for (o = cLISTOPx(expr)->op_first; o; o = OpSIBLING(o)) {
+        OP *child;
+        for (child = cLISTOPx(expr)->op_first; child; child = OpSIBLING(child)) {
 
-            if (o->op_type == OP_PADAV || o->op_type == OP_RV2AV) {
-                assert( !(o->op_flags  & OPf_WANT));
+            if (child->op_type == OP_PADAV || child->op_type == OP_RV2AV) {
+                assert( !(child->op_flags  & OPf_WANT));
                 /* push the array rather than its contents. The regex
                  * engine will retrieve and join the elements later */
-                o->op_flags |= (OPf_WANT_LIST | OPf_REF);
+                child->op_flags |= (OPf_WANT_LIST | OPf_REF);
                 continue;
             }
 
-            if (!(o->op_type == OP_NULL && (o->op_flags & OPf_SPECIAL)))
+            if (!(child->op_type == OP_NULL && (child->op_flags & OPf_SPECIAL)))
                 continue;
-            o->op_next = NULL; /* undo temporary hack from above */
-            scalar(o);
-            LINKLIST(o);
-            if (cLISTOPo->op_first->op_type == OP_LEAVE) {
-                LISTOP *leaveop = cLISTOPx(cLISTOPo->op_first);
+            child->op_next = NULL; /* undo temporary hack from above */
+            scalar(child);
+            LINKLIST(child);
+            if (cLISTOPx(child)->op_first->op_type == OP_LEAVE) {
+                LISTOP *leaveop = cLISTOPx(cLISTOPx(child)->op_first);
                 /* skip ENTER */
                 assert(leaveop->op_first->op_type == OP_ENTER);
                 assert(OpHAS_SIBLING(leaveop->op_first));
-                o->op_next = OpSIBLING(leaveop->op_first);
+                child->op_next = OpSIBLING(leaveop->op_first);
                 /* skip leave */
                 assert(leaveop->op_flags & OPf_KIDS);
                 assert(leaveop->op_last->op_next == (OP*)leaveop);
@@ -8077,7 +8077,7 @@ Perl_pmruntime(pTHX_ OP *o, OP *expr, OP *repl, UV flags, I32 floor)
             }
             else {
                 /* skip SCOPE */
-                OP *scope = cLISTOPo->op_first;
+                OP *scope = cLISTOPx(child)->op_first;
                 assert(scope->op_type == OP_SCOPE);
                 assert(scope->op_flags & OPf_KIDS);
                 scope->op_next = NULL; /* stop on last op */
@@ -8092,15 +8092,15 @@ Perl_pmruntime(pTHX_ OP *o, OP *expr, OP *repl, UV flags, I32 floor)
              * to the same optree later (where hopefully it won't do any
              * harm as it can't convert an op to multiconcat if it's
              * already been converted */
-            optimize_optree(o);
+            optimize_optree(child);
 
             /* have to peep the DOs individually as we've removed it from
              * the op_next chain */
-            CALL_PEEP(o);
-            S_prune_chain_head(&(o->op_next));
+            CALL_PEEP(child);
+            S_prune_chain_head(&(child->op_next));
             if (is_compiletime)
                 /* runtime finalizes as part of finalizing whole tree */
-                finalize_optree(o);
+                finalize_optree(child);
         }
     }
     else if (expr->op_type == OP_PADAV || expr->op_type == OP_RV2AV) {