[all-commits] [llvm/llvm-project] 239ca8: [IR] Add elementwise modifier to atomicrmw (#189517)

[Yonah Goldberg via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 239ca8d6c13a5c05a2363247e02edf29d2f253a2
      https://github.com/llvm/llvm-project/commit/239ca8d6c13a5c05a2363247e02edf29d2f253a2
  Author: Yonah Goldberg <ygoldberg at nvidia.com>
  Date:   2026-05-04 (Mon, 04 May 2026)

  Changed paths:
    M llvm/docs/LangRef.rst
    M llvm/include/llvm/AsmParser/LLToken.h
    M llvm/include/llvm/Bitcode/LLVMBitCodes.h
    M llvm/include/llvm/IR/IRBuilder.h
    M llvm/include/llvm/IR/Instructions.h
    M llvm/lib/AsmParser/LLLexer.cpp
    M llvm/lib/AsmParser/LLParser.cpp
    M llvm/lib/Bitcode/Reader/BitcodeReader.cpp
    M llvm/lib/Bitcode/Writer/BitcodeWriter.cpp
    M llvm/lib/IR/AsmWriter.cpp
    M llvm/lib/IR/Instruction.cpp
    M llvm/lib/IR/Instructions.cpp
    M llvm/lib/IR/Verifier.cpp
    M llvm/test/Assembler/atomic.ll
    A llvm/test/Assembler/invalid-atomicrmw-elementwise.ll
    A llvm/test/Bitcode/atomicrmw-elementwise.ll
    M llvm/test/Bitcode/compatibility.ll
    M llvm/unittests/Analysis/AliasAnalysisTest.cpp
    M llvm/unittests/IR/VerifierTest.cpp

  Log Message:
  -----------
  [IR] Add elementwise modifier to atomicrmw (#189517)

This PR implements the IR side modifications of [[RFC] Add elementwise
modifier to atomicrmw](https://discourse.llvm.org/t/rfc-add-elementwise-modifier-to-atomicrmw/90134).

Design Decisions:

- In the IR, the current atomicrmw record layout looks like: [ptrty,
ptr, valty, val, operation, vol, ordering, syncscope, align]. To encode
elementwise, I decided to pack it into the operation field, which also
contains the math op (i.e. fadd, fmin, add etc...). I could have changed
the record structure, but that would be slightly more complicated.
- elementwise vector atomics can be vectors of integers because we can always scalarize legally
- elementwise vector atomics need to have power of 2 size. We can potentially remove this restriction later.

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