[all-commits] [llvm/llvm-project] dde000: [DataLayout][LangRef] Split non-integral and unsta...

[Alexander Richardson via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: dde000a7d619ab2032f3e721edc850fb421e50cd
      https://github.com/llvm/llvm-project/commit/dde000a7d619ab2032f3e721edc850fb421e50cd
  Author: Alexander Richardson <alexrichardson at google.com>
  Date:   2025-09-23 (Tue, 23 Sep 2025)

  Changed paths:
    M llvm/docs/LangRef.rst
    M llvm/include/llvm/IR/DataLayout.h
    M llvm/lib/IR/DataLayout.cpp
    M llvm/test/Transforms/InstSimplify/ConstProp/inttoptr-gep-index-width.ll
    M llvm/test/Transforms/SimplifyCFG/switch_create-custom-dl.ll
    M llvm/unittests/IR/DataLayoutTest.cpp

  Log Message:
  -----------
  [DataLayout][LangRef] Split non-integral and unstable pointer properties

This commit adds finer-grained versions of isNonIntegralAddressSpace() and
isNonIntegralPointerType() where the current semantics prohibit
introduction of both ptrtoint and inttoptr instructions. The current
semantics are too strict for some targets (e.g. AMDGPU/CHERI) where
ptrtoint has a stable value, but the pointer has additional metadata.
Currently, marking a pointer address space as non-integral also marks it
as having an unstable bitwise representation (e.g. when pointers can be
changed by a copying GC). This property inhibits a lot of
optimizations that are perfectly legal for other non-integral pointers
such as fat pointers or CHERI capabilities that have a well-defined
bitwise representation but can't be created with only an address.

This change splits the properties of non-integral pointers and allows
for address spaces to be marked as unstable or non-integral (or both)
independently using the 'p' part of the DataLayout string.
A 'u' following the p marks the address space as unstable and specifying
a index width != representation width marks it as non-integral.
Finally, we also add an 'e' flag to mark pointers with external state
(such as the CHERI capability validity) state. These pointers require
special handling of loads and stores in addition to being non-integral.

This does not change the checks in any of the passes yet - we
currently keep the existing non-integral behaviour. In the future I plan
to audit calls to DL.isNonIntegral[PointerType]() and replace them with
the DL.mustNotIntroduce{IntToPtr,PtrToInt}() checks that allow for more
optimizations.

RFC: https://discourse.llvm.org/t/rfc-finer-grained-non-integral-pointer-properties/83176

Reviewed By: nikic, krzysz00

Pull Request: https://github.com/llvm/llvm-project/pull/105735



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