From 5dc3b3b28cd3b0581733e6839acde11d33c94ee0 Mon Sep 17 00:00:00 2001
From: David Nadlinger <code@klickverbot.at>
Date: Sat, 25 Jul 2020 02:18:10 +0100
Subject: [PATCH] compiler: Handle None-returning function calls used as values

GitHub: Fixes #1493.
---
 artiq/compiler/transforms/llvm_ir_generator.py |  5 +++++
 artiq/test/lit/codegen/none_retval.py          | 11 +++++++++++
 2 files changed, 16 insertions(+)
 create mode 100644 artiq/test/lit/codegen/none_retval.py

diff --git a/artiq/compiler/transforms/llvm_ir_generator.py b/artiq/compiler/transforms/llvm_ir_generator.py
index ca302412d..0d753c991 100644
--- a/artiq/compiler/transforms/llvm_ir_generator.py
+++ b/artiq/compiler/transforms/llvm_ir_generator.py
@@ -1462,6 +1462,11 @@ class LLVMIRGenerator:
         else:
             llcall = llresult = self.llbuilder.call(llfun, llargs, name=insn.name)
 
+            if isinstance(llresult.type, ll.VoidType):
+                # We have NoneType-returning functions return void, but None is
+                # {} elsewhere.
+                llresult = ll.Constant(llunit, [])
+
             # Never add TBAA nowrite metadata to a functon with sret!
             # This leads to miscompilations.
             if types.is_c_function(functiontyp) and 'nowrite' in functiontyp.flags:
diff --git a/artiq/test/lit/codegen/none_retval.py b/artiq/test/lit/codegen/none_retval.py
new file mode 100644
index 000000000..ed2c9eb25
--- /dev/null
+++ b/artiq/test/lit/codegen/none_retval.py
@@ -0,0 +1,11 @@
+# RUN: %python -m artiq.compiler.testbench.llvmgen %s
+
+def make_none():
+    return None
+
+def take_arg(arg):
+    pass
+
+def run():
+    retval = make_none()
+    take_arg(retval)