diff --git a/loopy/check.py b/loopy/check.py
index a871508b9ddfa320d219c4767f22b6257a95a726..8022d91eed51cc6aa07ecb7d4910f33fb855fb9e 100644
--- a/loopy/check.py
+++ b/loopy/check.py
@@ -26,13 +26,11 @@ THE SOFTWARE.
 from islpy import dim_type
 import islpy as isl
 from loopy.symbolic import WalkMapper
-from loopy.diagnostic import LoopyError, LoopyWarning
+from loopy.diagnostic import LoopyError, WriteRaceConditionWarning, warn
 
 import logging
 logger = logging.getLogger(__name__)
 
-from loopy.diagnostic import WriteRaceConditionError
-
 
 # {{{ sanity checks run during scheduling
 
@@ -167,11 +165,12 @@ def check_for_write_races(kernel):
                     raceable_parallel_insn_inames - assignee_inames
 
             if race_inames:
-                raise WriteRaceConditionError(
+                warn(kernel, "write_race(%s)" % insn.id,
                         "instruction '%s' contains a write race: "
                         "instruction will be run across parallel iname(s) "
                         "'%s', which is/are not referenced in the lhs index"
-                        % (insn.id, ",".join(race_inames)))
+                        % (insn.id, ",".join(race_inames)),
+                        WriteRaceConditionWarning)
 
 
 def check_for_orphaned_user_hardware_axes(kernel):
diff --git a/loopy/diagnostic.py b/loopy/diagnostic.py
index dd2860a0e882e2567b508803ad94d945d0248ee4..e305038b89c4312ff415357a760cb08cd7b20135 100644
--- a/loopy/diagnostic.py
+++ b/loopy/diagnostic.py
@@ -40,9 +40,24 @@ class LoopyAdvisory(LoopyWarningBase):
 class ParameterFinderWarning(LoopyWarningBase):
     pass
 
+
+class WriteRaceConditionWarning(LoopyWarningBase):
+    pass
+
 # }}}
 
 
+def warn(kernel, id, text, type=LoopyWarning):
+    if id in kernel.silenced_warnings:
+        return
+
+    text += (" (add '%s' to silenced_warnings kernel argument to disable)"
+            % id)
+
+    from warnings import warn
+    warn(text, type)
+
+
 # {{{ errors
 
 class LoopyError(RuntimeError):
@@ -53,10 +68,6 @@ class CannotBranchDomainTree(LoopyError):
     pass
 
 
-class WriteRaceConditionError(LoopyError):
-    pass
-
-
 class TypeInferenceFailure(LoopyError):
     pass
 
@@ -66,4 +77,7 @@ class DependencyTypeInferenceFailure(TypeInferenceFailure):
 
 # }}}
 
+
+
+
 # vim: foldmethod=marker
diff --git a/loopy/kernel/__init__.py b/loopy/kernel/__init__.py
index 8a7c53f8460471aca3f68d549a0f17de1b48fe4b..423dba4e6e987526cb45442532f86b055272b443 100644
--- a/loopy/kernel/__init__.py
+++ b/loopy/kernel/__init__.py
@@ -124,6 +124,8 @@ class LoopKernel(Record):
         it will be scheduled. (This applies to inames with non-parallel
         implementation tags.)
 
+    .. attribute:: silenced_warnings
+
     .. attribute:: applied_iname_rewrites
 
         A list of past substitution dictionaries that
@@ -154,6 +156,8 @@ class LoopKernel(Record):
 
             iname_slab_increments={},
             loop_priority=[],
+            silenced_warnings=[],
+
             applied_iname_rewrites=[],
             cache_manager=None,
             index_dtype=np.int32,
@@ -250,6 +254,7 @@ class LoopKernel(Record):
                 assumptions=assumptions,
                 iname_slab_increments=iname_slab_increments,
                 loop_priority=loop_priority,
+                silenced_warnings=silenced_warnings,
                 temporary_variables=temporary_variables,
                 local_sizes=local_sizes,
                 iname_to_tag=iname_to_tag,
diff --git a/loopy/kernel/creation.py b/loopy/kernel/creation.py
index 157b7cbf353edfa5a6d894dee99cdcae573f8693..91a654c3787b965ba2127b9669593f1a4001ce25 100644
--- a/loopy/kernel/creation.py
+++ b/loopy/kernel/creation.py
@@ -401,9 +401,10 @@ def guess_kernel_args_if_requested(domains, instructions, temporary_variables,
     temp_var_names = set(temporary_variables.iterkeys())
 
     for insn in instructions:
-        if insn.temp_var_type is not None:
-            (assignee_var_name, _), = insn.assignees_and_indices()
-            temp_var_names.add(assignee_var_name)
+        if isinstance(insn, ExpressionInstruction):
+            if insn.temp_var_type is not None:
+                (assignee_var_name, _), = insn.assignees_and_indices()
+                temp_var_names.add(assignee_var_name)
 
     # }}}
 
@@ -430,7 +431,7 @@ def guess_kernel_args_if_requested(domains, instructions, temporary_variables,
         all_params.update(dom.get_var_names(dim_type.param))
     all_params = all_params - all_inames
 
-    new_arg_names = (all_names - not_new_arg_names) | all_params
+    new_arg_names = (all_names | all_params) - not_new_arg_names
 
     # }}}
 
@@ -438,8 +439,8 @@ def guess_kernel_args_if_requested(domains, instructions, temporary_variables,
         irf = IndexRankFinder(name)
 
         for insn in instructions:
-            irf(submap(insn.expression, insn.id))
-            irf(submap(insn.assignee, insn.id))
+            insn.with_transformed_expressions(
+                    lambda expr: irf(submap(expr, insn.id)))
 
         if not irf.index_ranks:
             return 0
@@ -880,11 +881,17 @@ def make_kernel(device, domains, instructions, kernel_data=["..."], **kwargs):
     :arg local_sizes: A dictionary from integers to integers, mapping
         workgroup axes to their sizes, e.g. *{0: 16}* forces axis 0 to be
         length 16.
+    :arg silenced_warnings: a list (or semicolon-separated string) or warnings
+        to silence
     """
 
     defines = kwargs.pop("defines", {})
     default_order = kwargs.pop("default_order", "C")
     default_offset = kwargs.pop("default_offset", 0)
+    silenced_warnings = kwargs.pop("silenced_warnings", [])
+
+    if isinstance(silenced_warnings, str):
+        silenced_warnings = silenced_warnings.split(";")
 
     # {{{ separate temporary variables and arguments
 
diff --git a/loopy/kernel/data.py b/loopy/kernel/data.py
index c844995d61e590237d2203be9becbd86adc57b12..832096a32594e03c5263f2b143715e9c5a022aa8 100644
--- a/loopy/kernel/data.py
+++ b/loopy/kernel/data.py
@@ -556,8 +556,7 @@ def _remove_common_indentation(code):
     code = code.lstrip("//CL//")
 
     if not code.startswith("\n"):
-        raise ValueError("expected newline as first character "
-                "in literal lines")
+        return code
 
     lines = code.split("\n")
     while lines[0].strip() == "":
diff --git a/loopy/preprocess.py b/loopy/preprocess.py
index d41a36405c7a0e556860c797d2a203b43c1bca5d..c9adbf0c9354add723a2966ef18599813a05e85b 100644
--- a/loopy/preprocess.py
+++ b/loopy/preprocess.py
@@ -25,7 +25,9 @@ THE SOFTWARE.
 
 import pyopencl as cl
 import pyopencl.characterize as cl_char
-from loopy.diagnostic import LoopyError, LoopyWarning
+from loopy.diagnostic import (
+        LoopyError, LoopyWarning, WriteRaceConditionWarning, warn,
+        LoopyAdvisory)
 
 import logging
 logger = logging.getLogger(__name__)
@@ -250,15 +252,16 @@ def mark_local_temporaries(kernel):
 
             if (locparallel_assignee_inames != locparallel_compute_inames
                     and bool(locparallel_assignee_inames)):
-                from loopy.check import WriteRaceConditionError
-                raise WriteRaceConditionError("instruction '%s' looks invalid: "
+                warn(kernel, "write_race_local(%s)" % insn_id,
+                        "instruction '%s' looks invalid: "
                         "it assigns to indices based on local IDs, but "
                         "its temporary '%s' cannot be made local because "
                         "a write race across the iname(s) '%s' would emerge. "
                         "(Do you need to add an extra iname to your prefetch?)"
                         % (insn_id, temp_var.name, ", ".join(
                             locparallel_compute_inames
-                            - locparallel_assignee_inames)))
+                            - locparallel_assignee_inames)),
+                        WriteRaceConditionWarning)
 
             wants_to_be_local_per_insn.append(
                     locparallel_assignee_inames == locparallel_compute_inames
@@ -268,9 +271,8 @@ def mark_local_temporaries(kernel):
                     and bool(locparallel_compute_inames))
 
         if not wants_to_be_local_per_insn:
-            from warnings import warn
-            from loopy.diagnostic import LoopyAdvisory
-            warn("temporary variable '%s' never written, eliminating"
+            warn(kernel, "temp_to_write(%s)" % temp_var.name,
+                    "temporary variable '%s' never written, eliminating"
                     % temp_var.name, LoopyAdvisory)
 
         is_local = wants_to_be_local_per_insn[0]
diff --git a/test/test_linalg.py b/test/test_linalg.py
index 374b43e6f2f1c75887800df541bdf5bdb88b21ab..6cbc81d4649107c7a67212eabdc350cef780685e 100644
--- a/test/test_linalg.py
+++ b/test/test_linalg.py
@@ -23,6 +23,8 @@ THE SOFTWARE.
 """
 
 
+import pytest
+import sys
 import numpy as np
 import pyopencl as cl
 import pyopencl.array as cl_array
@@ -490,6 +492,7 @@ def test_image_matrix_mul_ilp(ctx_factory):
             parameters={})
 
 
+@pytest.mark.skipif("sys.version_info < (2,6)")
 def test_ilp_race_matmul(ctx_factory):
     dtype = np.float32
     ctx = ctx_factory()
@@ -513,11 +516,14 @@ def test_ilp_race_matmul(ctx_factory):
     knl = lp.split_iname(knl, "k", 2)
     knl = lp.add_prefetch(knl, 'b', ["k_inner"])
 
-    from loopy.check import WriteRaceConditionError
-    import pytest
-    with pytest.raises(WriteRaceConditionError):
+    from loopy.diagnostic import WriteRaceConditionWarning
+    from warnings import catch_warnings
+    with catch_warnings(record=True) as warn_list:
         list(lp.generate_loop_schedules(knl))
 
+        assert any(isinstance(w.message, WriteRaceConditionWarning)
+                for w in warn_list)
+
 
 def test_fancy_matrix_mul(ctx_factory):
     dtype = np.float32
@@ -587,7 +593,6 @@ def test_small_batched_matvec(ctx_factory):
 
 
 if __name__ == "__main__":
-    import sys
     if len(sys.argv) > 1:
         exec(sys.argv[1])
     else:
diff --git a/test/test_loopy.py b/test/test_loopy.py
index e6d8a61adb303665c630387eda10bb761e82feeb..111c596867b1a0bcb52432add7a069d5a9ca401f 100644
--- a/test/test_loopy.py
+++ b/test/test_loopy.py
@@ -23,10 +23,12 @@ THE SOFTWARE.
 """
 
 
+import sys
 import numpy as np
 import loopy as lp
 import pyopencl as cl
 import pyopencl.clrandom  # noqa
+import pytest
 
 import logging
 logger = logging.getLogger(__name__)
@@ -895,6 +897,7 @@ def test_double_sum(ctx_factory):
 
 # {{{ test race detection
 
+@pytest.mark.skipif("sys.version_info < (2,6)")
 def test_ilp_write_race_detection_global(ctx_factory):
     ctx = ctx_factory()
 
@@ -912,11 +915,14 @@ def test_ilp_write_race_detection_global(ctx_factory):
 
     knl = lp.tag_inames(knl, dict(j="ilp"))
 
-    from loopy.check import WriteRaceConditionError
-    import pytest
-    with pytest.raises(WriteRaceConditionError):
+    from loopy.diagnostic import WriteRaceConditionWarning
+    from warnings import catch_warnings
+    with catch_warnings(record=True) as warn_list:
         list(lp.generate_loop_schedules(knl))
 
+        assert any(isinstance(w.message, WriteRaceConditionWarning)
+                for w in warn_list)
+
 
 def test_ilp_write_race_avoidance_local(ctx_factory):
     ctx = ctx_factory()
@@ -1192,7 +1198,6 @@ def test_c_instruction(ctx_factory):
 
 
 if __name__ == "__main__":
-    import sys
     if len(sys.argv) > 1:
         exec(sys.argv[1])
     else: