Fix the gumbel softmax by casting to f32. (#2928)

Author: LaurentMazare

candle-nn/src/sampling.rs

@@ -8,13 +8,16 @@ pub fn gumbel_softmax<D: candle::shape::Dim>(
 ) -> Result<Tensor> {
     if temperature <= 0.0 {
         logits.argmax(dim)
-    } else if temperature == 1.0 {
-        let minus_g = logits.rand_like(1e-7, 0.999)?.log()?.neg()?.log()?;
-        let sampled = (logits - minus_g)?.argmax(dim)?;
-        Ok(sampled)
     } else {
+        // Cast to f32, doing the Gumbel softmax in bf16 is a bit unstable.
+        let logits = logits.to_dtype(candle::DType::F32)?;
         let minus_g = logits.rand_like(1e-7, 0.999)?.log()?.neg()?.log()?;
-        let sampled = (logits + minus_g * (-temperature))?.argmax(dim)?;
-        Ok(sampled)
+        if temperature == 1.0 {
+            let sampled = (logits - minus_g)?.argmax(dim)?;
+            Ok(sampled)
+        } else {
+            let sampled = (logits + minus_g * (-temperature))?.argmax(dim)?;
+            Ok(sampled)
+        }
     }
 }