diff --git a/dfdx-core/Cargo.toml b/dfdx-core/Cargo.toml
index 5309ef7c..0f6cd5c6 100644
--- a/dfdx-core/Cargo.toml
+++ b/dfdx-core/Cargo.toml
@@ -35,7 +35,7 @@ num-traits = { workspace = true }
 safetensors = { workspace = true, optional = true }
 memmap2 = { workspace = true, optional = true }
 half = { version = "2.3.1", optional = true, features = ["num-traits", "rand_distr"] }
-gemm = { version = "0.16.14", default-features = false, optional = true, features = ["rayon"] }
+gemm = { version = "0.17.1", default-features = false, optional = true, features = ["rayon"] }
 rayon = { version = "1.7.0", optional = true }
 libm = { workspace = true }
 wgpu = { version = "0.18.0", features = ["glsl", "spirv"], optional = true }
diff --git a/dfdx-core/src/data/collate.rs b/dfdx-core/src/data/collate.rs
index d38a2a67..5f52d636 100644
--- a/dfdx-core/src/data/collate.rs
+++ b/dfdx-core/src/data/collate.rs
@@ -55,6 +55,7 @@ impl<A, B> Collate for Vec<(A, B)> {
 impl<'a, A, B> Collate for Vec<&'a (A, B)> {
     type Collated = (Vec<&'a A>, Vec<&'a B>);
     fn collated(self) -> Self::Collated {
+        #[allow(clippy::map_identity)]
         self.into_iter().map(|(a, b)| (a, b)).unzip()
     }
 }
diff --git a/dfdx-core/src/lib.rs b/dfdx-core/src/lib.rs
index 31e61643..c126db2c 100644
--- a/dfdx-core/src/lib.rs
+++ b/dfdx-core/src/lib.rs
@@ -128,44 +128,6 @@ pub mod prelude {
     pub use crate::tensor_ops::*;
 }
 
-/// Sets a CPU `sse` flag to flush denormal floating point numbers to zero. The opposite of this is [keep_denormals()].
-///
-/// Some resources:
-/// 1. [Effects of Flush-To-Zero mode](https://developer.arm.com/documentation/dui0473/c/neon-and-vfp-programming/the-effects-of-using-flush-to-zero-mode?lang=en)
-/// 2. [When to use Flush-To-Zero mode](https://developer.arm.com/documentation/dui0473/c/neon-and-vfp-programming/when-to-use-flush-to-zero-mode?lang=en)
-pub fn flush_denormals_to_zero() {
-    #[cfg(all(target_arch = "x86", target_feature = "sse"))]
-    {
-        use std::arch::x86::{_MM_FLUSH_ZERO_ON, _MM_SET_FLUSH_ZERO_MODE};
-        unsafe { _MM_SET_FLUSH_ZERO_MODE(_MM_FLUSH_ZERO_ON) }
-    }
-
-    #[cfg(all(target_arch = "x86_64", target_feature = "sse"))]
-    {
-        use std::arch::x86_64::{_MM_FLUSH_ZERO_ON, _MM_SET_FLUSH_ZERO_MODE};
-        unsafe { _MM_SET_FLUSH_ZERO_MODE(_MM_FLUSH_ZERO_ON) }
-    }
-}
-
-/// Sets a CPU flag to keep denormal floating point numbers. The opposite of this is [flush_denormals_to_zero()].
-///
-/// Some resources:
-/// 1. [Effects of Flush-To-Zero mode](https://developer.arm.com/documentation/dui0473/c/neon-and-vfp-programming/the-effects-of-using-flush-to-zero-mode?lang=en)
-/// 2. [When to use Flush-To-Zero mode](https://developer.arm.com/documentation/dui0473/c/neon-and-vfp-programming/when-to-use-flush-to-zero-mode?lang=en)
-pub fn keep_denormals() {
-    #[cfg(all(target_arch = "x86", target_feature = "sse"))]
-    {
-        use std::arch::x86::{_MM_FLUSH_ZERO_OFF, _MM_SET_FLUSH_ZERO_MODE};
-        unsafe { _MM_SET_FLUSH_ZERO_MODE(_MM_FLUSH_ZERO_OFF) }
-    }
-
-    #[cfg(all(target_arch = "x86_64", target_feature = "sse"))]
-    {
-        use std::arch::x86_64::{_MM_FLUSH_ZERO_OFF, _MM_SET_FLUSH_ZERO_MODE};
-        unsafe { _MM_SET_FLUSH_ZERO_MODE(_MM_FLUSH_ZERO_OFF) }
-    }
-}
-
 #[cfg(test)]
 pub(crate) mod tests {
     pub use num_traits::{Float, NumCast, Zero};
diff --git a/dfdx-core/src/shapes/shape.rs b/dfdx-core/src/shapes/shape.rs
index 184337cd..c3e27121 100644
--- a/dfdx-core/src/shapes/shape.rs
+++ b/dfdx-core/src/shapes/shape.rs
@@ -69,6 +69,30 @@ where
     }
 }
 
+impl<const N: usize> core::ops::Sub<Const<N>> for usize {
+    type Output = usize;
+    fn sub(self, _: Const<N>) -> Self::Output {
+        self.size() - N
+    }
+}
+impl<const N: usize> core::ops::Sub<usize> for Const<N> {
+    type Output = usize;
+    fn sub(self, rhs: usize) -> Self::Output {
+        N - rhs.size()
+    }
+}
+
+#[cfg(feature = "nightly")]
+impl<const N: usize, const M: usize> core::ops::Sub<Const<N>> for Const<M>
+where
+    Const<{ M - N }>: Sized,
+{
+    type Output = Const<{ M - N }>;
+    fn sub(self, _: Const<N>) -> Self::Output {
+        Const
+    }
+}
+
 impl<const N: usize> core::ops::Mul<Const<N>> for usize {
     type Output = usize;
     fn mul(self, _: Const<N>) -> Self::Output {
diff --git a/dfdx-core/src/tensor/gradients.rs b/dfdx-core/src/tensor/gradients.rs
index 86974ec6..d24e2e32 100644
--- a/dfdx-core/src/tensor/gradients.rs
+++ b/dfdx-core/src/tensor/gradients.rs
@@ -153,7 +153,7 @@ impl<E, D: Storage<E>> Gradients<E, D> {
     #[inline]
     pub(crate) fn many_and_ref<L: Shape, R: Shape>(
         &mut self,
-        ls: &Vec<impl Tensorlike<L, E, D>>,
+        ls: &[impl Tensorlike<L, E, D>],
         r: &impl Tensorlike<R, E, D>,
     ) -> (Vec<&mut D::Vec>, &D::Vec) {
         for i in 0..ls.len() {
diff --git a/dfdx-core/src/tensor_ops/utilities/device.rs b/dfdx-core/src/tensor_ops/utilities/device.rs
index 8cbc2137..91f87cf6 100644
--- a/dfdx-core/src/tensor_ops/utilities/device.rs
+++ b/dfdx-core/src/tensor_ops/utilities/device.rs
@@ -114,25 +114,49 @@ pub trait Device<E: Dtype>:
     + crate::tensor_ops::axpy::AxpyKernel<E>
 
     // conv1d
-    + super::super::conv1d::Conv1DKernel<E>
+    + NonCudnnCuda<E>
+{
+}
+
+#[cfg(feature = "cudnn")]
+pub trait NonCudnnCuda<E: Dtype> {}
+
+#[cfg(not(feature = "cudnn"))]
+pub trait NonCudnnCuda<E: Dtype>:
+    // conv1d
+    super::super::conv1d::Conv1DKernel<E>
 {
 }
 
 #[cfg(feature = "f16")]
-impl Device<f16> for crate::tensor::Cpu {}
-#[cfg(feature = "f16")]
-impl Device<AMP<f16>> for crate::tensor::Cpu {}
+mod f16_ {
+    use super::*;
+    impl Device<f16> for crate::tensor::Cpu {}
+    impl NonCudnnCuda<f16> for crate::tensor::Cpu {}
+    impl Device<AMP<f16>> for crate::tensor::Cpu {}
+    impl NonCudnnCuda<AMP<f16>> for crate::tensor::Cpu {}
+}
 impl Device<f32> for crate::tensor::Cpu {}
+impl NonCudnnCuda<f32> for crate::tensor::Cpu {}
 impl Device<f64> for crate::tensor::Cpu {}
+impl NonCudnnCuda<f64> for crate::tensor::Cpu {}
 
 #[cfg(all(feature = "cuda", feature = "f16"))]
-impl Device<f16> for crate::tensor::Cuda {}
-#[cfg(all(feature = "cuda", feature = "f16"))]
-impl Device<AMP<f16>> for crate::tensor::Cuda {}
-#[cfg(feature = "cuda")]
-impl Device<f32> for crate::tensor::Cuda {}
+mod cuda_f16 {
+    use super::*;
+    impl Device<f16> for crate::tensor::Cuda {}
+    impl NonCudnnCuda<f16> for crate::tensor::Cuda {}
+    impl Device<AMP<f16>> for crate::tensor::Cuda {}
+    impl NonCudnnCuda<AMP<f16>> for crate::tensor::Cuda {}
+}
 #[cfg(feature = "cuda")]
-impl Device<f64> for crate::tensor::Cuda {}
+mod cuda {
+    use super::*;
+    impl Device<f32> for crate::tensor::Cuda {}
+    impl NonCudnnCuda<f32> for crate::tensor::Cuda {}
+    impl Device<f64> for crate::tensor::Cuda {}
+    impl NonCudnnCuda<f64> for crate::tensor::Cuda {}
+}
 
 // TODO: How can we implement this for f16 when WGSL doesn't support f16 yet?
 // #[cfg(all(feature = "webgpu", feature = "f16"))]
@@ -140,7 +164,11 @@ impl Device<f64> for crate::tensor::Cuda {}
 // #[cfg(all(feature = "webgpu", feature = "f16"))]
 // impl Device<AMP<f16>> for crate::tensor::Webgpu {}
 #[cfg(feature = "webgpu")]
-impl Device<f32> for crate::tensor::Webgpu {}
+mod webgpu {
+    use super::*;
+    impl Device<f32> for crate::tensor::Webgpu {}
+    impl NonCudnnCuda<f32> for crate::tensor::Webgpu {}
+}
 
 // TODO: How can we implement this for f64 when WGSL doesn't support f64 yet?
 // #[cfg(feature = "webgpu")]
diff --git a/dfdx/examples/12-mnist.rs b/dfdx/examples/12-mnist.rs
index 705d14c8..00d43452 100644
--- a/dfdx/examples/12-mnist.rs
+++ b/dfdx/examples/12-mnist.rs
@@ -62,9 +62,6 @@ type Mlp = (
 const BATCH_SIZE: usize = 32;
 
 fn main() {
-    // ftz substantially improves performance
-    dfdx::flush_denormals_to_zero();
-
     let mnist_path = std::env::args()
         .nth(1)
         .unwrap_or_else(|| "./datasets/MNIST/raw".to_string());