[PATCH] D18367: Introduce llvm.load.relative intrinsic.

[Peter Collingbourne via llvm-commits]

pcc created this revision.
pcc added reviewers: rafael, rjmccall.
pcc added a subscriber: llvm-commits.

This intrinsic takes two arguments, ``%ptr`` and ``%offset``. It loads
a 32-bit value from the address ``%ptr + %offset``, adds ``%ptr`` to that
value and returns it. The constant folder specifically recognizes the form of
this intrinsic and the constant initializers it may load from; if a loaded
constant initializer is known to have the form ``i32 trunc(x - %ptr)``,
the intrinsic call is folded to ``x``.

LLVM provides that the calculation of such a constant initializer will
not overflow at link time under the medium code model if ``x`` is an
``unnamed_addr`` function, however it does not provide the same for a constant
initializer folded into a function body; this intrinsic can be used to avoid
the possibility of overflows when loading from such a constant.

Depends on http://reviews.llvm.org/D17938

http://reviews.llvm.org/D18367

Files:
  docs/LangRef.rst
  include/llvm/CodeGen/Passes.h
  include/llvm/IR/Intrinsics.td
  include/llvm/InitializePasses.h
  lib/Analysis/InstructionSimplify.cpp
  lib/CodeGen/CMakeLists.txt
  lib/CodeGen/CodeGen.cpp
  lib/CodeGen/LLVMTargetMachine.cpp
  lib/CodeGen/PreISelIntrinsicLowering.cpp
  test/CodeGen/Generic/stop-after.ll
  test/Transforms/InstSimplify/load-relative-32.ll
  test/Transforms/InstSimplify/load-relative.ll
  test/Transforms/PreISelIntrinsicLowering/load-relative.ll
  tools/opt/opt.cpp

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