diff --git a/tests/unit/test_fp4_isolate.py b/tests/unit/test_fp4_isolate.py
new file mode 100644
index 00000000..ea4134a4
--- /dev/null
+++ b/tests/unit/test_fp4_isolate.py
@@ -0,0 +1,98 @@
+"""Isolate which function causes the LLVM ERROR."""
+import torch
+import cutlass
+import cutlass.cute as cute
+import cutlass.torch as cutlass_torch
+import sys
+
+from dsv4.kernels.gemm.fp4_quant import (
+    fp8_e4m3_from_float32,
+    fp8_e4m3_to_float32,
+    quantize_e2m1_nibble,
+    round_rne_u0_8,
+    abs_scaled_to_e2m1_idx,
+)
+
+test = sys.argv[1] if len(sys.argv) > 1 else "round_rne"
+
+if test == "round_rne":
+    @cute.kernel
+    def k(inp: cute.Tensor, out: cute.Tensor):
+        tidx, _, _ = cute.arch.thread_idx()
+        if tidx == cutlass.Int32(0):
+            x = cute.arch.load(inp.iterator, cutlass.Float32)
+            r = round_rne_u0_8(x)
+            cute.arch.store(out.iterator, r)
+
+elif test == "abs_scaled":
+    @cute.kernel
+    def k(inp: cute.Tensor, out: cute.Tensor):
+        tidx, _, _ = cute.arch.thread_idx()
+        if tidx == cutlass.Int32(0):
+            x = cute.arch.load(inp.iterator, cutlass.Float32)
+            r = abs_scaled_to_e2m1_idx(x)
+            cute.arch.store(out.iterator, r)
+
+elif test == "fp8_encode":
+    @cute.kernel
+    def k(inp: cute.Tensor, out: cute.Tensor):
+        tidx, _, _ = cute.arch.thread_idx()
+        if tidx == cutlass.Int32(0):
+            x = cute.arch.load(inp.iterator, cutlass.Float32)
+            r = fp8_e4m3_from_float32(x)
+            cute.arch.store(out.iterator, r)
+
+elif test == "fp8_decode":
+    @cute.kernel
+    def k(inp: cute.Tensor, out: cute.Tensor):
+        tidx, _, _ = cute.arch.thread_idx()
+        if tidx == cutlass.Int32(0):
+            x = cute.arch.load(inp.iterator, cutlass.Int32)
+            r = fp8_e4m3_to_float32(x)
+            cute.arch.store(out.iterator, r)
+
+elif test == "e2m1_quant":
+    @cute.kernel
+    def k(val: cute.Tensor, scale: cute.Tensor, out: cute.Tensor):
+        tidx, _, _ = cute.arch.thread_idx()
+        if tidx == cutlass.Int32(0):
+            v = cute.arch.load(val.iterator, cutlass.Float32)
+            s = cute.arch.load(scale.iterator, cutlass.Float32)
+            r = quantize_e2m1_nibble(v, s)
+            cute.arch.store(out.iterator, r)
+
+
+if __name__ == "__main__":
+    print(f"Test: {test}")
+    if test == "e2m1_quant":
+        v = torch.tensor([1.5], dtype=torch.float32, device='cuda')
+        s = torch.tensor([1.0], dtype=torch.float32, device='cuda')
+        o = torch.zeros(1, dtype=torch.int32, device='cuda')
+        vc = cutlass_torch.from_dlpack(v).mark_layout_dynamic(leading_dim=0)
+        sc = cutlass_torch.from_dlpack(s).mark_layout_dynamic(leading_dim=0)
+        oc = cutlass_torch.from_dlpack(o).mark_layout_dynamic(leading_dim=0)
+        print("Compiling...")
+        compiled = cute.compile(k, vc, sc, oc)
+        print("Running...")
+        compiled(vc, sc, oc)
+        print(f"Result: {o.item()}")
+    elif test == "fp8_decode":
+        x = torch.tensor([126], dtype=torch.int32, device='cuda')
+        o = torch.zeros(1, dtype=torch.float32, device='cuda')
+        xc = cutlass_torch.from_dlpack(x).mark_layout_dynamic(leading_dim=0)
+        oc = cutlass_torch.from_dlpack(o).mark_layout_dynamic(leading_dim=0)
+        print("Compiling...")
+        compiled = cute.compile(k, xc, oc)
+        print("Running...")
+        compiled(xc, oc)
+        print(f"Result: {o.item()}")
+    else:
+        x = torch.tensor([3.7], dtype=torch.float32, device='cuda')
+        o = torch.zeros(1, dtype=torch.int32, device='cuda')
+        xc = cutlass_torch.from_dlpack(x).mark_layout_dynamic(leading_dim=0)
+        oc = cutlass_torch.from_dlpack(o).mark_layout_dynamic(leading_dim=0)
+        print("Compiling...")
+        compiled = cute.compile(k, xc, oc)
+        print("Running...")
+        compiled(xc, oc)
+        print(f"Result: {o.item()}")
diff --git a/tests/unit/test_fp4_isolate_runner.py b/tests/unit/test_fp4_isolate_runner.py
new file mode 100644
index 00000000..1aa3c1e1
--- /dev/null
+++ b/tests/unit/test_fp4_isolate_runner.py
@@ -0,0 +1,10 @@
+"""Run each function isolation test in a separate process."""
+import subprocess, sys
+for t in ["round_rne", "abs_scaled", "fp8_encode", "fp8_decode", "e2m1_quant"]:
+    print(f"\n{'='*50}\n{t}\n{'='*50}")
+    r = subprocess.run([sys.executable, "tests/unit/test_fp4_isolate.py", t],
+                       capture_output=True, text=True, timeout=120)
+    print(r.stdout[-300:] if r.stdout else "")
+    if r.stderr:
+        print(f"ERR: ...{r.stderr[-200:]}")
+    print(f"Exit: {r.returncode}")