[PATCH] D100445: [RS4GC] Introduce intrinsics to get base ptr and offset

[Yevgeny Rouban via Phabricator via llvm-commits]

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There can be a need for some optimizations to get (base, offset) for any GC pointer. The base can be calculated by generating needed instructions as it is done by the //RewriteStatepointsForGC::findBasePointer()// function. The offset can be calculated in the same way. Though to not expose the base calculation and to make the offset calculation as simple as //ptrtoint(derived_ptr) - ptrtoint(base_ptr)//, which is illegal outside RS4GC, this patch introduces 2 intrinsics:

- declare i8 addrspace(1)* @llvm.experimental.gc.get.pointer.base(i8 addrspace(1)* readnone nocapture %base_ptr) nounwind readnone willreturn "gc-leaf-function"
- declare i64 @llvm.experimental.gc.get.pointer.offset(i8 addrspace(1)* readnone nocapture %base_ptr) nounwind readnone willreturn "gc-leaf-function"

These intrinsics are inlined by RS4GC along with generation of statepoint sequences.

With these new intrinsics the GC parseable lowering for atomic memcpy intrinsics (D88861 <https://reviews.llvm.org/D88861>) could be implemented as a separate pass.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D100445

Files:
  llvm/docs/Statepoints.rst
  llvm/include/llvm/IR/IRBuilder.h
  llvm/include/llvm/IR/Intrinsics.td
  llvm/lib/IR/IRBuilder.cpp
  llvm/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp
  llvm/test/Transforms/RewriteStatepointsForGC/intrinsics.ll
  llvm/utils/TableGen/CodeGenIntrinsics.h
  llvm/utils/TableGen/CodeGenTarget.cpp
  llvm/utils/TableGen/IntrinsicEmitter.cpp

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