bpo-32836: Remove obsolete code from symtable pass (GH-5680)

When comprehensions switched to using a nested scope, the old
code for generating a temporary name to hold the accumulation
target became redundant, but was never actually removed.

Patch by Nitish Chandra.
(cherry picked from commit 3a087be)

Co-authored-by: Nitish Chandra <[email protected]>

Author: miss-islington

Include/symtable.h

@@ -60,7 +60,6 @@ typedef struct _symtable_entry {
     int ste_col_offset;      /* offset of first line of block */
     int ste_opt_lineno;      /* lineno of last exec or import * */
     int ste_opt_col_offset;  /* offset of last exec or import * */
-    int ste_tmpname;         /* counter for listcomp temp vars */
     struct symtable *ste_table;
 } PySTEntryObject;
 

Misc/NEWS.d/next/Core and Builtins/2018-02-14-12-35-47.bpo-32836.bThJnx.rst

@@ -0,0 +1 @@
+Don't use temporary variables in cases of list/dict/set comprehensions

Python/symtable.c

@@ -69,7 +69,6 @@ ste_new(struct symtable *st, identifier name, _Py_block_ty block,
     ste->ste_varkeywords = 0;
     ste->ste_opt_lineno = 0;
     ste->ste_opt_col_offset = 0;
-    ste->ste_tmpname = 0;
     ste->ste_lineno = lineno;
     ste->ste_col_offset = col_offset;
 
@@ -1082,24 +1081,6 @@ symtable_add_def(struct symtable *st, PyObject *name, int flag)
     } \
 }
 
-static int
-symtable_new_tmpname(struct symtable *st)
-{
-    char tmpname[256];
-    identifier tmp;
-
-    PyOS_snprintf(tmpname, sizeof(tmpname), "_[%d]",
-                  ++st->st_cur->ste_tmpname);
-    tmp = PyUnicode_InternFromString(tmpname);
-    if (!tmp)
-        return 0;
-    if (!symtable_add_def(st, tmp, DEF_LOCAL))
-        return 0;
-    Py_DECREF(tmp);
-    return 1;
-}
-
-
 static int
 symtable_record_directive(struct symtable *st, identifier name, stmt_ty s)
 {
@@ -1723,7 +1704,6 @@ symtable_handle_comprehension(struct symtable *st, expr_ty e,
                               expr_ty elt, expr_ty value)
 {
     int is_generator = (e->kind == GeneratorExp_kind);
-    int needs_tmp = !is_generator;
     comprehension_ty outermost = ((comprehension_ty)
                                     asdl_seq_GET(generators, 0));
     /* Outermost iterator is evaluated in current scope */
@@ -1742,11 +1722,6 @@ symtable_handle_comprehension(struct symtable *st, expr_ty e,
         symtable_exit_block(st, (void *)e);
         return 0;
     }
-    /* Allocate temporary name if needed */
-    if (needs_tmp && !symtable_new_tmpname(st)) {
-        symtable_exit_block(st, (void *)e);
-        return 0;
-    }
     VISIT(st, expr, outermost->target);
     VISIT_SEQ(st, expr, outermost->ifs);
     VISIT_SEQ_TAIL(st, comprehension, generators, 1);