[all-commits] [llvm/llvm-project] f1cc0b: [IR] Introduce `dead_on_return` attribute

[Antonio Frighetto via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: f1cc0b607b03548028db3ca57bb057b2599b1711
      https://github.com/llvm/llvm-project/commit/f1cc0b607b03548028db3ca57bb057b2599b1711
  Author: Antonio Frighetto <me at antoniofrighetto.com>
  Date:   2025-07-02 (Wed, 02 Jul 2025)

  Changed paths:
    M llvm/docs/LangRef.rst
    M llvm/include/llvm/Bitcode/LLVMBitCodes.h
    M llvm/include/llvm/IR/Argument.h
    M llvm/include/llvm/IR/Attributes.td
    M llvm/lib/Bitcode/Reader/BitcodeReader.cpp
    M llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
    M llvm/lib/IR/Attributes.cpp
    M llvm/lib/IR/Function.cpp
    M llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
    M llvm/lib/Transforms/Utils/CodeExtractor.cpp
    M llvm/test/Bitcode/attributes.ll
    M llvm/test/Transforms/DeadStoreElimination/simple.ll
    A llvm/test/Verifier/dead-on-return.ll

  Log Message:
  -----------
  [IR] Introduce `dead_on_return` attribute

Add `dead_on_return` attribute, which is meant to be taken advantage
by the frontend, and states that the memory pointed to by the argument
is dead upon function return. As with `byval`, it is supposed to be
used for passing aggregates by value. The difference lies in the ABI:
`byval` implies that the pointer is explicitly passed as argument to
the callee (during codegen the copy is emitted as per byval contract),
whereas a `dead_on_return`-marked argument implies that the copy
already exists in the IR, is located at a specific stack offset within
the caller, and this memory will not be read further by the caller upon
callee return – or otherwise poison, if read before being written.

RFC: https://discourse.llvm.org/t/rfc-add-dead-on-return-attribute/86871.



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