[compile] raise on compile_size implicit padding (#32343)

Signed-off-by: dolpm <34420038+dolpm@users.noreply.github.com>

tests/compile/test_config.py

@@ -470,3 +470,68 @@ def test_cached_compilation_config(default_vllm_config):
 
     code = " ".join(code)
     assert "torch.ops._C.static_scaled_fp8_quant.default(" in code
+
+
+def test_compile_sizes_padding_validation():
+    """Test that compile_sizes with values that would be padded raises an error."""
+    # cudagraph_capture_sizes=[1, 2, 4, 8] means:
+    # - size 1 -> padded to 1
+    # - size 2 -> padded to 2
+    # - size 3 -> padded to 4
+    # - size 4 -> padded to 4
+    # - size 5 -> padded to 8
+    # etc.
+    # So compile_sizes=[3] should fail because 3 would be padded to 4
+
+    with pytest.raises(ValueError, match="would be padded to"):
+        config = CompilationConfig(
+            cudagraph_capture_sizes=[1, 2, 4, 8],
+            max_cudagraph_capture_size=8,
+            compile_sizes=[3],
+        )
+        config.post_init_cudagraph_sizes()
+
+    with pytest.raises(ValueError, match="would be padded to"):
+        config = CompilationConfig(
+            cudagraph_capture_sizes=[1, 2, 4, 8],
+            max_cudagraph_capture_size=8,
+            compile_sizes=[5],
+        )
+        config.post_init_cudagraph_sizes()
+
+    config = CompilationConfig(
+        cudagraph_capture_sizes=[1, 2, 4, 8],
+        max_cudagraph_capture_size=8,
+        compile_sizes=[1, 2, 4, 8],
+    )
+    config.post_init_cudagraph_sizes()
+    assert sorted(config.compile_sizes) == [1, 2, 4, 8]
+
+    config = CompilationConfig(
+        cudagraph_capture_sizes=[1, 2, 4, 8],
+        max_cudagraph_capture_size=8,
+        compile_sizes=["cudagraph_capture_sizes"],
+    )
+    config.post_init_cudagraph_sizes()
+    assert sorted(config.compile_sizes) == [1, 2, 4, 8]
+
+    # When cudagraphs are disabled (max_cudagraph_capture_size=0),
+    # padding validation should be skipped
+    config = CompilationConfig(
+        cudagraph_capture_sizes=[],
+        max_cudagraph_capture_size=0,
+        compile_sizes=[3, 5, 7],  # would be invalid with cudagraphs
+    )
+    config.post_init_cudagraph_sizes()
+    assert sorted(config.compile_sizes) == [3, 5, 7]
+
+    # When cudagraph_mode is NONE but capture_sizes is non-empty,
+    # padding validation should still be skipped
+    config = CompilationConfig(
+        cudagraph_capture_sizes=[1, 2, 4, 8],
+        max_cudagraph_capture_size=8,
+        cudagraph_mode=CUDAGraphMode.NONE,
+        compile_sizes=[3, 5, 7],  # would be invalid if cudagraphs were enabled
+    )
+    config.post_init_cudagraph_sizes()
+    assert sorted(config.compile_sizes) == [3, 5, 7]