[all-commits] [llvm/llvm-project] 1a42f7: [clang][dataflow] Don't analyze templated declarat...

[martinboehme via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 1a42f795587b9d57291d009989aace6efd0a7a7f
      https://github.com/llvm/llvm-project/commit/1a42f795587b9d57291d009989aace6efd0a7a7f
  Author: Martin Braenne <mboehme at google.com>
  Date:   2023-05-15 (Mon, 15 May 2023)

  Changed paths:
    M clang/include/clang/Analysis/FlowSensitive/ControlFlowContext.h
    M clang/lib/Analysis/FlowSensitive/ControlFlowContext.cpp
    M clang/lib/Analysis/FlowSensitive/DataflowAnalysisContext.cpp
    M clang/lib/Analysis/FlowSensitive/Transfer.cpp
    M clang/unittests/Analysis/FlowSensitive/TestingSupport.h
    M clang/unittests/Analysis/FlowSensitive/TransferTest.cpp
    M clang/unittests/Analysis/FlowSensitive/TypeErasedDataflowAnalysisTest.cpp

  Log Message:
  -----------
  [clang][dataflow] Don't analyze templated declarations.

Attempting to analyze templated code doesn't have a good cost-benefit ratio. We
have so far done a best-effort attempt at this, but maintaining this support has
an ongoing high maintenance cost because the AST for templates can violate a lot
of the invariants that otherwise hold for the AST of concrete code. As just one
example, in concrete code the operand of a UnaryOperator '*' is always a prvalue
(https://godbolt.org/z/s3e5xxMd1), but in templates this isn't true
(https://godbolt.org/z/6W9xxGvoM).

Further rationale for not analyzing templates:

* The semantics of a template itself are weakly defined; semantics can depend
  strongly on the concrete template arguments. Analyzing the template itself (as
  opposed to an instantiation) therefore has limited value.

* Analyzing templates requires a lot of special-case code that isn't necessary
  for concrete code because dependent types are hard to deal with and the AST
  violates invariants that otherwise hold for concrete code (see above).

* There's precedent in that neither Clang Static Analyzer nor the flow-sensitive
  warnings in Clang (such as uninitialized variables) support analyzing
  templates.

Reviewed By: gribozavr2, xazax.hun

Differential Revision: https://reviews.llvm.org/D150352