Fix fft for integer overflow (#2161)

mlx/backend/metal/fft.cpp

@@ -632,7 +632,7 @@ void fft_op(
   func_consts.push_back(make_int(&rader_m, 3));
 
   // The overall number of FFTs we're going to compute for this input
-  int size = out.dtype() == float32 ? out.size() : in.size();
+  size_t size = out.dtype() == float32 ? out.size() : in.size();
   if (real && inverse && four_step_params.required) {
     size = out.size();
   }
@@ -659,8 +659,6 @@ void fft_op(
     // We can perform 2 RFFTs at once so the batch size is halved.
     batch_size = (batch_size + 2 - 1) / 2;
   }
-  int out_buffer_size = out.size();
-
   auto& compute_encoder = d.get_command_encoder(s.index);
   auto in_type_str = in.dtype() == float32 ? "float" : "float2";
   auto out_type_str = out.dtype() == float32 ? "float" : "float2";

mlx/backend/metal/kernels/fft/readwrite.h

@@ -98,7 +98,7 @@ struct ReadWriter {
   }
 
   METAL_FUNC void load() const {
-    int batch_idx = elem.x * grid.y * n;
+    size_t batch_idx = size_t(elem.x * grid.y) * n;
     short tg_idx = elem.y * grid.z + elem.z;
     short max_index = grid.y * n - 2;
 
@@ -121,7 +121,7 @@ struct ReadWriter {
   }
 
   METAL_FUNC void write() const {
-    int batch_idx = elem.x * grid.y * n;
+    size_t batch_idx = size_t(elem.x * grid.y) * n;
     short tg_idx = elem.y * grid.z + elem.z;
     short max_index = grid.y * n - 2;
 
@@ -144,7 +144,7 @@ struct ReadWriter {
 
   // Padded IO for Bluestein's algorithm
   METAL_FUNC void load_padded(int length, const device float2* w_k) const {
-    int batch_idx = elem.x * grid.y * length + elem.y * length;
+    size_t batch_idx = size_t(elem.x * grid.y) * length + elem.y * length;
     int fft_idx = elem.z;
     int m = grid.z;
 
@@ -161,7 +161,7 @@ struct ReadWriter {
   }
 
   METAL_FUNC void write_padded(int length, const device float2* w_k) const {
-    int batch_idx = elem.x * grid.y * length + elem.y * length;
+    size_t batch_idx = size_t(elem.x * grid.y) * length + elem.y * length;
     int fft_idx = elem.z;
     int m = grid.z;
     float2 inv_factor = {1.0f / n, -1.0f / n};
@@ -261,7 +261,7 @@ METAL_FUNC bool ReadWriter<float, float2>::out_of_bounds() const {
 
 template <>
 METAL_FUNC void ReadWriter<float, float2>::load() const {
-  int batch_idx = elem.x * grid.y * n * 2 + elem.y * n * 2;
+  size_t batch_idx = size_t(elem.x * grid.y) * n * 2 + elem.y * n * 2;
   threadgroup float2* seq_buf = buf + elem.y * n;
 
   // No out of bounds accesses on odd batch sizes
@@ -283,7 +283,8 @@ template <>
 METAL_FUNC void ReadWriter<float, float2>::write() const {
   short n_over_2 = (n / 2) + 1;
 
-  int batch_idx = elem.x * grid.y * n_over_2 * 2 + elem.y * n_over_2 * 2;
+  size_t batch_idx =
+      size_t(elem.x * grid.y) * n_over_2 * 2 + elem.y * n_over_2 * 2;
   threadgroup float2* seq_buf = buf + elem.y * n;
 
   int grid_index = elem.x * grid.y + elem.y;
@@ -317,7 +318,7 @@ template <>
 METAL_FUNC void ReadWriter<float, float2>::load_padded(
     int length,
     const device float2* w_k) const {
-  int batch_idx = elem.x * grid.y * length * 2 + elem.y * length * 2;
+  size_t batch_idx = size_t(elem.x * grid.y) * length * 2 + elem.y * length * 2;
   threadgroup float2* seq_buf = buf + elem.y * n;
 
   // No out of bounds accesses on odd batch sizes
@@ -345,8 +346,8 @@ METAL_FUNC void ReadWriter<float, float2>::write_padded(
     int length,
     const device float2* w_k) const {
   int length_over_2 = (length / 2) + 1;
-  int batch_idx =
+  size_t batch_idx =
-      elem.x * grid.y * length_over_2 * 2 + elem.y * length_over_2 * 2;
+      size_t(elem.x * grid.y) * length_over_2 * 2 + elem.y * length_over_2 * 2;
   threadgroup float2* seq_buf = buf + elem.y * n + length - 1;
 
   int grid_index = elem.x * grid.y + elem.y;
@@ -397,7 +398,8 @@ METAL_FUNC bool ReadWriter<float2, float>::out_of_bounds() const {
 template <>
 METAL_FUNC void ReadWriter<float2, float>::load() const {
   short n_over_2 = (n / 2) + 1;
-  int batch_idx = elem.x * grid.y * n_over_2 * 2 + elem.y * n_over_2 * 2;
+  size_t batch_idx =
+      size_t(elem.x * grid.y) * n_over_2 * 2 + elem.y * n_over_2 * 2;
   threadgroup float2* seq_buf = buf + elem.y * n;
 
   // No out of bounds accesses on odd batch sizes
@@ -458,8 +460,8 @@ METAL_FUNC void ReadWriter<float2, float>::load_padded(
   int n_over_2 = (n / 2) + 1;
   int length_over_2 = (length / 2) + 1;
 
-  int batch_idx =
+  size_t batch_idx =
-      elem.x * grid.y * length_over_2 * 2 + elem.y * length_over_2 * 2;
+      size_t(elem.x * grid.y) * length_over_2 * 2 + elem.y * length_over_2 * 2;
   threadgroup float2* seq_buf = buf + elem.y * n;
 
   // No out of bounds accesses on odd batch sizes
@@ -503,7 +505,7 @@ template <>
 METAL_FUNC void ReadWriter<float2, float>::write_padded(
     int length,
     const device float2* w_k) const {
-  int batch_idx = elem.x * grid.y * length * 2 + elem.y * length * 2;
+  size_t batch_idx = size_t(elem.x * grid.y) * length * 2 + elem.y * length * 2;
   threadgroup float2* seq_buf = buf + elem.y * n + length - 1;
 
   int grid_index = elem.x * grid.y + elem.y;