Add keep_in_fp32_modules support (#20683)

* add `keep_in_fp32_modules` support

* pass it as class attribute

* few modifs

- make tests `slow`
- fix logic

* better logic

* fix failing test

* `bfloat16` support

* Update src/transformers/modeling_utils.py

Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>

* fix

* simplify tests

* simplify tests

* fix test

* modify message

* more checks

* fix failing tests

* add more conditions

- add `is_accelerate_available`
- fixes pipleine tests that failed

* add suggestions

* Update src/transformers/modeling_utils.py

Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>

* fix failing `bnb` test

* add last safety checker

Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>

tests/models/t5/test_modeling_t5.py

@@ -19,7 +19,14 @@ import tempfile
 import unittest
 
 from transformers import T5Config, is_torch_available
-from transformers.testing_utils import require_sentencepiece, require_tokenizers, require_torch, slow, torch_device
+from transformers.testing_utils import (
+    require_accelerate,
+    require_sentencepiece,
+    require_tokenizers,
+    require_torch,
+    slow,
+    torch_device,
+)
 from transformers.utils import cached_property
 
 from ...generation.test_utils import GenerationTesterMixin
@@ -820,6 +827,50 @@ def use_task_specific_params(model, task):
     model.config.update(model.config.task_specific_params[task])
 
 
+@require_torch
+@require_accelerate
+@require_tokenizers
+@slow
+class T5ModelFp16Tests(unittest.TestCase):
+    def test_fp16_fp32_conversion(self):
+        r"""
+        A test to check whether the argument `keep_in_fp32_modules` correctly does its job
+        """
+        # Load without using `accelerate`
+        model = T5ForConditionalGeneration.from_pretrained("t5-small", torch_dtype=torch.float16)
+        self.assertTrue(model.decoder.block[0].layer[2].DenseReluDense.wo.weight.dtype == torch.float32)
+        self.assertTrue(model.decoder.block[0].layer[2].DenseReluDense.wi.weight.dtype == torch.float16)
+
+        # Load without in bf16
+        model = T5ForConditionalGeneration.from_pretrained("t5-small", torch_dtype=torch.bfloat16)
+        self.assertTrue(model.decoder.block[0].layer[2].DenseReluDense.wo.weight.dtype == torch.bfloat16)
+        self.assertTrue(model.decoder.block[0].layer[2].DenseReluDense.wi.weight.dtype == torch.bfloat16)
+
+        # Load using `accelerate` in bf16
+        model = T5ForConditionalGeneration.from_pretrained("t5-small", torch_dtype=torch.bfloat16, device_map="auto")
+        self.assertTrue(model.decoder.block[0].layer[2].DenseReluDense.wo.weight.dtype == torch.bfloat16)
+        self.assertTrue(model.decoder.block[0].layer[2].DenseReluDense.wi.weight.dtype == torch.bfloat16)
+
+        # Load using `accelerate` in bf16
+        model = T5ForConditionalGeneration.from_pretrained(
+            "t5-small", torch_dtype=torch.bfloat16, low_cpu_mem_usage=True
+        )
+        self.assertTrue(model.decoder.block[0].layer[2].DenseReluDense.wo.weight.dtype == torch.bfloat16)
+        self.assertTrue(model.decoder.block[0].layer[2].DenseReluDense.wi.weight.dtype == torch.bfloat16)
+
+        # Load without using `accelerate`
+        model = T5ForConditionalGeneration.from_pretrained(
+            "t5-small", torch_dtype=torch.float16, low_cpu_mem_usage=True
+        )
+        self.assertTrue(model.decoder.block[0].layer[2].DenseReluDense.wo.weight.dtype == torch.float32)
+        self.assertTrue(model.decoder.block[0].layer[2].DenseReluDense.wi.weight.dtype == torch.float16)
+
+        # Load using `accelerate`
+        model = T5ForConditionalGeneration.from_pretrained("t5-small", torch_dtype=torch.float16, device_map="auto")
+        self.assertTrue(model.decoder.block[0].layer[2].DenseReluDense.wo.weight.dtype == torch.float32)
+        self.assertTrue(model.decoder.block[0].layer[2].DenseReluDense.wi.weight.dtype == torch.float16)
+
+
 @require_torch
 @require_sentencepiece
 @require_tokenizers