Add TorchLogsumexpVisitor (#89)

Suggest using `torch.logsumexp(x)` instead of
`torch.log(torch.sum(torch.exp(x))`.

https://pytorch.org/docs/stable/generated/torch.logsumexp.html

Author: kit1980

tests/fixtures/misc/checker/logsumexp.py

@@ -0,0 +1,14 @@
+import torch
+a = torch.randn(5)
+b = torch.randn(5)
+
+# logsumexp
+y = torch.log(torch.sum(torch.exp(x), 1, keepdim=True))
+y = torch.log(torch.sum(torch.exp(2.5 + x), 1))
+
+# not logsumexp
+y = torch.log(torch.sum(torch.exp(x), 1, keepdim=True) + 2.5)
+y = torch.log(torch.sum(torch.exp(x) + 2.5, 1))
+y = torch.log(2 + x)
+y = torch.sum(torch.log(torch.exp(x)), 1)
+y = torch.exp(torch.sum(torch.log(x), 1, keepdim=True))

tests/fixtures/misc/checker/logsumexp.txt

@@ -0,0 +1,2 @@
+6:5 TOR108 Use numerically stabilized `torch.logsumexp`.
+7:5 TOR108 Use numerically stabilized `torch.logsumexp`.

tests/test_torchfix.py

@@ -47,6 +47,7 @@ def pytest_generate_tests(metafunc):
                     "TOR105",
                     "TOR106",
                     "TOR107",
+                    "TOR108",
                 },
             ),
             (None, set(GET_ALL_ERROR_CODES()) - exclude_set),

torchfix/torchfix.py

@@ -11,6 +11,7 @@
     TorchDeprecatedSymbolsVisitor,
     TorchExpm1Visitor,
     TorchLog1pVisitor,
+    TorchLogsumexpVisitor,
     TorchNonPublicAliasVisitor,
     TorchReentrantCheckpointVisitor,
     TorchRequireGradVisitor,
@@ -32,6 +33,7 @@
     TorchDeprecatedSymbolsVisitor,
     TorchExpm1Visitor,
     TorchLog1pVisitor,
+    TorchLogsumexpVisitor,
     TorchNonPublicAliasVisitor,
     TorchRequireGradVisitor,
     TorchReentrantCheckpointVisitor,

torchfix/visitors/__init__.py

@@ -3,6 +3,7 @@
 from .misc import (
     TorchExpm1Visitor,
     TorchLog1pVisitor,
+    TorchLogsumexpVisitor,
     TorchReentrantCheckpointVisitor,
     TorchRequireGradVisitor,
 )
@@ -19,6 +20,7 @@
     "TorchDeprecatedSymbolsVisitor",
     "TorchExpm1Visitor",
     "TorchLog1pVisitor",
+    "TorchLogsumexpVisitor",
     "TorchNonPublicAliasVisitor",
     "TorchReentrantCheckpointVisitor",
     "TorchRequireGradVisitor",

torchfix/visitors/misc/__init__.py

@@ -96,7 +96,6 @@ class TorchLog1pVisitor(TorchVisitor):
 
     def visit_Call(self, node):
         if self.get_qualified_name_for_call(node) == "torch.log":
-
             if m.matches(
                 node,
                 m.Call(
@@ -114,7 +113,6 @@ def visit_Call(self, node):
                     ],
                 ),
             ):
-
                 self.add_violation(
                     node,
                     error_code=self.ERRORS[0].error_code,
@@ -154,3 +152,41 @@ def visit_BinaryOperation(self, node):
                     message=self.ERRORS[0].message(),
                     replacement=None,
                 )
+
+
+class TorchLogsumexpVisitor(TorchVisitor):
+    """
+    Suggest using `torch.logsumexp(x)` instead of `torch.log(torch.sum(torch.exp(x))`.
+    """
+
+    ERRORS = [
+        TorchError(
+            "TOR108",
+            ("Use numerically stabilized `torch.logsumexp`."),
+        )
+    ]
+
+    def visit_Call(self, node):
+        if self.get_qualified_name_for_call(node) == "torch.log":
+            if m.matches(
+                node,
+                m.Call(
+                    args=[
+                        m.Arg(m.Call(args=[m.Arg(m.Call()), m.ZeroOrMore()])),
+                        m.ZeroOrMore(),
+                    ]
+                ),
+            ):
+                if self.get_qualified_name_for_call(node.args[0].value) == "torch.sum":
+                    if (
+                        self.get_qualified_name_for_call(
+                            node.args[0].value.args[0].value
+                        )
+                        == "torch.exp"
+                    ):
+                        self.add_violation(
+                            node,
+                            error_code=self.ERRORS[0].error_code,
+                            message=self.ERRORS[0].message(),
+                            replacement=None,
+                        )