#1920: when considering a block starting by "while 0", the compiler optimized the
whole construct away, even when an 'else' clause is present::
while 0:
print("no")
else:
print("yes")
did not generate any code at all.
Now the compiler emits the 'else' block, like it already does for 'if' statements.
Backport of r60265.
diff --git a/Lib/test/test_grammar.py b/Lib/test/test_grammar.py
index 76483f6..89e9e67 100644
--- a/Lib/test/test_grammar.py
+++ b/Lib/test/test_grammar.py
@@ -511,6 +511,15 @@
while 0: pass
else: pass
+# Issue1920: "while 0" is optimized away,
+# ensure that the "else" clause is still present.
+x = 0
+while 0:
+ x = 1
+else:
+ x = 2
+assert x == 2
+
print 'for_stmt' # 'for' exprlist 'in' exprlist ':' suite ['else' ':' suite]
for i in 1, 2, 3: pass
for i, j, k in (): pass
diff --git a/Misc/NEWS b/Misc/NEWS
index 8b0084a..4913c79 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -12,6 +12,11 @@
Core and builtins
-----------------
+- Issue #1920: "while 0" statements were completely removed by the compiler,
+ even in the presence of an "else" clause, which is supposed to be run when
+ the condition is false. Now the compiler correctly emits bytecode for the
+ "else" suite.
+
- A few crashers fixed: weakref_in_del.py (issue #1377858);
loosing_dict_ref.py (issue #1303614, test67.py);
borrowed_ref_[34].py (not in tracker).
diff --git a/Python/compile.c b/Python/compile.c
index 0e824ca..8e96ddf 100644
--- a/Python/compile.c
+++ b/Python/compile.c
@@ -2256,8 +2256,11 @@
basicblock *loop, *orelse, *end, *anchor = NULL;
int constant = expr_constant(s->v.While.test);
- if (constant == 0)
+ if (constant == 0) {
+ if (s->v.While.orelse)
+ VISIT_SEQ(c, stmt, s->v.While.orelse);
return 1;
+ }
loop = compiler_new_block(c);
end = compiler_new_block(c);
if (constant == -1) {