transforms.inferencer: infer a monomorphic type for slice ":"

artiq/compiler/transforms/inferencer.py

@@ -202,6 +202,10 @@ class Inferencer(algorithm.Visitor):
                         value.loc, None)
 
     def visit_SliceT(self, node):
+        if (node.lower, node.upper, node.step) == (None, None, None):
+            self._unify(node.type, builtins.TInt32(),
+                        node.loc, None)
+        else:
             self._unify(node.type, builtins.TInt(),
                         node.loc, None)
             for operand in (node.lower, node.upper, node.step):

lit-test/test/inferencer/slice.py

@@ -0,0 +1,6 @@
+# RUN: %python -m artiq.compiler.testbench.inferencer %s >%t
+# RUN: OutputCheck %s --file-to-check=%t
+
+x = [0]
+# CHECK-L: [::int(width=32)]
+x[:] = [1]