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| author | Peter Collingbourne <peter@pcc.me.uk> | 2016-04-22 21:18:02 +0000 |
|---|---|---|
| committer | Peter Collingbourne <peter@pcc.me.uk> | 2016-04-22 21:18:02 +0000 |
| commit | 74eabdd998cb907f33bf6362af7dd5dbb10b24b8 (patch) | |
| tree | 20ba36ac8e310f69806479a939d2ce46e633da7a /docs | |
| parent | 6217a62bc009d55e160dbb694f2e94a22c80809f (diff) | |
Introduce llvm.load.relative intrinsic.
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 this guarantee 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.
Differential Revision: http://reviews.llvm.org/D18367
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@267223 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'docs')
| -rw-r--r-- | docs/LangRef.rst | 25 |
1 files changed, 25 insertions, 0 deletions
diff --git a/docs/LangRef.rst b/docs/LangRef.rst index 2cb71bb78ce..d588b0514b0 100644 --- a/docs/LangRef.rst +++ b/docs/LangRef.rst @@ -12361,6 +12361,31 @@ if"); and this allows for "check widening" type optimizations. ``@llvm.experimental.guard`` cannot be invoked. +'``llvm.load.relative``' Intrinsic +^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ + +Syntax: +""""""" + +:: + + declare i8* @llvm.load.relative.iN(i8* %ptr, iN %offset) argmemonly nounwind readonly + +Overview: +""""""""" + +This intrinsic 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 this guarantee 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. + Stack Map Intrinsics -------------------- |