diff --git a/artiq/compiler/targets.py b/artiq/compiler/targets.py
index 34f85d85f..ba79e0121 100644
--- a/artiq/compiler/targets.py
+++ b/artiq/compiler/targets.py
@@ -46,12 +46,14 @@ class RunTool:
 def _dump(target, kind, suffix, content):
     if target is not None:
         print("====== {} DUMP ======".format(kind.upper()), file=sys.stderr)
-        content_bytes = bytes(content(), 'utf-8')
+        content_value = content()
+        if isinstance(content_value, str):
+            content_value = bytes(content_value, 'utf-8')
         if target == "":
             file = tempfile.NamedTemporaryFile(suffix=suffix, delete=False)
         else:
             file = open(target + suffix, "wb")
-        file.write(content_bytes)
+        file.write(content_value)
         file.close()
         print("{} dumped as {}".format(kind, file.name), file=sys.stderr)
 
diff --git a/artiq/compiler/transforms/llvm_ir_generator.py b/artiq/compiler/transforms/llvm_ir_generator.py
index 8082595f9..474dbd883 100644
--- a/artiq/compiler/transforms/llvm_ir_generator.py
+++ b/artiq/compiler/transforms/llvm_ir_generator.py
@@ -569,7 +569,6 @@ class LLVMIRGenerator:
             if func.is_internal:
                 self.llfunction.linkage = 'private'
             if func.is_cold:
-                self.llfunction.calling_convention = 'coldcc'
                 self.llfunction.attributes.add('cold')
                 self.llfunction.attributes.add('noinline')
 
@@ -685,13 +684,17 @@ class LLVMIRGenerator:
                                        inbounds=True)
             llouterenv = self.llbuilder.load(llptr)
             llouterenv.metadata['invariant.load'] = self.empty_metadata
+            llouterenv.metadata['nonnull'] = self.empty_metadata
             return self.llptr_to_var(llouterenv, env_ty.params["$outer"], var_name)
 
     def process_GetLocal(self, insn):
         env = insn.environment()
         llptr = self.llptr_to_var(self.map(env), env.type, insn.var_name)
         llptr.name = "ptr.{}.{}".format(env.name, insn.var_name)
-        return self.llbuilder.load(llptr, name="val.{}.{}".format(env.name, insn.var_name))
+        llvalue = self.llbuilder.load(llptr, name="val.{}.{}".format(env.name, insn.var_name))
+        if isinstance(llvalue.type, ll.PointerType):
+            llvalue.metadata['nonnull'] = self.empty_metadata
+        return llvalue
 
     def process_SetLocal(self, insn):
         env = insn.environment()
@@ -810,9 +813,12 @@ class LLVMIRGenerator:
             else:
                 llptr = self.llbuilder.gep(obj, [self.llindex(0), self.llindex(index)],
                                            inbounds=True, name="ptr.{}".format(insn.name))
-                llval = self.llbuilder.load(llptr, name="val.{}".format(insn.name))
-                llval.metadata['invariant.load'] = self.empty_metadata
-                return llval
+                llvalue = self.llbuilder.load(llptr, name="val.{}".format(insn.name))
+                if types.is_instance(typ) and attr in typ.constant_attributes:
+                    llvalue.metadata['invariant.load'] = self.empty_metadata
+                if isinstance(llvalue.type, ll.PointerType):
+                    llvalue.metadata['nonnull'] = self.empty_metadata
+                return llvalue
 
     def process_SetAttr(self, insn):
         typ, attr = insn.object().type, insn.attr
@@ -840,7 +846,10 @@ class LLVMIRGenerator:
         llelts = self.llbuilder.extract_value(self.map(insn.list()), 1)
         llelt = self.llbuilder.gep(llelts, [self.map(insn.index())],
                                    inbounds=True)
-        return self.llbuilder.load(llelt)
+        llvalue = self.llbuilder.load(llelt)
+        if isinstance(llvalue.type, ll.PointerType):
+            llvalue.metadata['nonnull'] = self.empty_metadata
+        return llvalue
 
     def process_SetElem(self, insn):
         llelts = self.llbuilder.extract_value(self.map(insn.list()), 1)
@@ -1051,6 +1060,7 @@ class LLVMIRGenerator:
                                                inbounds=True)
                     llouterenv = self.llbuilder.load(llptr)
                     llouterenv.metadata['invariant.load'] = self.empty_metadata
+                    llouterenv.metadata['nonnull'] = self.empty_metadata
                     return self.llptr_to_var(llouterenv, env_ty.params["$outer"], var_name)
                 else:
                     return llenv
@@ -1311,9 +1321,6 @@ class LLVMIRGenerator:
             if types.is_c_function(functiontyp) and 'nowrite' in functiontyp.flags:
                 llcall.metadata['tbaa'] = self.tbaa_nowrite_call
 
-        if insn.is_cold:
-            llcall.cconv = 'coldcc'
-
         return llresult
 
     def process_Invoke(self, insn):
@@ -1347,9 +1354,6 @@ class LLVMIRGenerator:
             if types.is_c_function(functiontyp) and 'nowrite' in functiontyp.flags:
                 llcall.metadata['tbaa'] = self.tbaa_nowrite_call
 
-        if insn.is_cold:
-            llcall.cconv = 'coldcc'
-
         return llcall
 
     def _quote(self, value, typ, path):
diff --git a/artiq/test/lit/embedding/syscall_flags.py b/artiq/test/lit/embedding/syscall_flags.py
index 15636507f..7d2a10341 100644
--- a/artiq/test/lit/embedding/syscall_flags.py
+++ b/artiq/test/lit/embedding/syscall_flags.py
@@ -4,7 +4,7 @@
 from artiq.language.core import *
 from artiq.language.types import *
 
-# CHECK: call void @foo\(\), !dbg !\d+, !tbaa !\d+
+# CHECK: call void @foo\(\)(, !dbg !\d+)?, !tbaa !\d+
 
 # CHECK-L: ; Function Attrs: nounwind
 # CHECK-NEXT-L: declare void @foo()