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Update LangRef now that a DataLayout is mandatory.

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Reviewers: rafael, echristo

Reviewed By: rafael

Subscribers: rafael, llvm-commits

Differential Revision: http://reviews.llvm.org/D8230

From: Mehdi Amini <mehdi.amini@apple.com>

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@232283 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Mehdi Amini 2015-03-14 22:04:06 +00:00
parent cf4419f88b
commit 18233dc596
1 changed files with 42 additions and 41 deletions
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docs/LangRef.rst
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@ -998,7 +998,7 @@ Currently, only the following parameter attributes are defined:
This indicates that the parameter or return pointer is not null. This
attribute may only be applied to pointer typed parameters. This is not
checked or enforced by LLVM, the caller must ensure that the pointer
passed in is non-null, or the callee must ensure that the returned pointer
passed in is non-null, or the callee must ensure that the returned pointer
is non-null.
``dereferenceable(<n>)``
@ -1024,12 +1024,12 @@ string:
define void @f() gc "name" { ... }
The supported values of *name* includes those :ref:`built in to LLVM
The supported values of *name* includes those :ref:`built in to LLVM
<builtin-gc-strategies>` and any provided by loaded plugins. Specifying a GC
strategy will cause the compiler to alter its output in order to support the
named garbage collection algorithm. Note that LLVM itself does not contain a
strategy will cause the compiler to alter its output in order to support the
named garbage collection algorithm. Note that LLVM itself does not contain a
garbage collector, this functionality is restricted to generating machine code
which can interoperate with a collector provided externally.
which can interoperate with a collector provided externally.
.. _prefixdata:
@ -1526,11 +1526,12 @@ the code generator should use.
Instead, if specified, the target data layout is required to match what
the ultimate *code generator* expects. This string is used by the
mid-level optimizers to improve code, and this only works if it matches
what the ultimate code generator uses. If you would like to generate IR
that does not embed this target-specific detail into the IR, then you
don't have to specify the string. This will disable some optimizations
that require precise layout information, but this also prevents those
optimizations from introducing target specificity into the IR.
what the ultimate code generator uses. There is no way to generate IR
that does not embed this target-specific detail into the IR. If you
don't specify the string, the default specifications will be used to
generate a Data Layout and the optimization phases will operate
accordingly and introduce target specificity into the IR with respect to
these default specifications.
.. _langref_triple:
@ -3539,28 +3540,28 @@ for optimizations are prefixed with ``llvm.mem``.
'``llvm.mem.parallel_loop_access``' Metadata
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
The ``llvm.mem.parallel_loop_access`` metadata refers to a loop identifier,
or metadata containing a list of loop identifiers for nested loops.
The metadata is attached to memory accessing instructions and denotes that
no loop carried memory dependence exist between it and other instructions denoted
The ``llvm.mem.parallel_loop_access`` metadata refers to a loop identifier,
or metadata containing a list of loop identifiers for nested loops.
The metadata is attached to memory accessing instructions and denotes that
no loop carried memory dependence exist between it and other instructions denoted
with the same loop identifier.
Precisely, given two instructions ``m1`` and ``m2`` that both have the
``llvm.mem.parallel_loop_access`` metadata, with ``L1`` and ``L2`` being the
set of loops associated with that metadata, respectively, then there is no loop
carried dependence between ``m1`` and ``m2`` for loops in both ``L1`` and
Precisely, given two instructions ``m1`` and ``m2`` that both have the
``llvm.mem.parallel_loop_access`` metadata, with ``L1`` and ``L2`` being the
set of loops associated with that metadata, respectively, then there is no loop
carried dependence between ``m1`` and ``m2`` for loops in both ``L1`` and
``L2``.
As a special case, if all memory accessing instructions in a loop have
``llvm.mem.parallel_loop_access`` metadata that refers to that loop, then the
loop has no loop carried memory dependences and is considered to be a parallel
loop.
As a special case, if all memory accessing instructions in a loop have
``llvm.mem.parallel_loop_access`` metadata that refers to that loop, then the
loop has no loop carried memory dependences and is considered to be a parallel
loop.
Note that if not all memory access instructions have such metadata referring to
the loop, then the loop is considered not being trivially parallel. Additional
memory dependence analysis is required to make that determination. As a fail
safe mechanism, this causes loops that were originally parallel to be considered
sequential (if optimization passes that are unaware of the parallel semantics
Note that if not all memory access instructions have such metadata referring to
the loop, then the loop is considered not being trivially parallel. Additional
memory dependence analysis is required to make that determination. As a fail
safe mechanism, this causes loops that were originally parallel to be considered
sequential (if optimization passes that are unaware of the parallel semantics
insert new memory instructions into the loop body).
Example of a loop that is considered parallel due to its correct use of
@ -5604,17 +5605,17 @@ metadata name ``<index>`` corresponding to a metadata node with no
entries. The existence of the ``!invariant.load`` metadata on the
instruction tells the optimizer and code generator that the address
operand to this load points to memory which can be assumed unchanged.
Being invariant does not imply that a location is dereferenceable,
but it does imply that once the location is known dereferenceable
its value is henceforth unchanging.
Being invariant does not imply that a location is dereferenceable,
but it does imply that once the location is known dereferenceable
its value is henceforth unchanging.
The optional ``!nonnull`` metadata must reference a single
metadata name ``<index>`` corresponding to a metadata node with no
entries. The existence of the ``!nonnull`` metadata on the
instruction tells the optimizer that the value loaded is known to
never be null. This is analogous to the ''nonnull'' attribute
on parameters and return values. This metadata can only be applied
to loads of a pointer type.
on parameters and return values. This metadata can only be applied
to loads of a pointer type.
Semantics:
""""""""""
@ -7414,8 +7415,8 @@ Accurate Garbage Collection Intrinsics
--------------------------------------
LLVM's support for `Accurate Garbage Collection <GarbageCollection.html>`_
(GC) requires the frontend to generate code containing appropriate intrinsic
calls and select an appropriate GC strategy which knows how to lower these
(GC) requires the frontend to generate code containing appropriate intrinsic
calls and select an appropriate GC strategy which knows how to lower these
intrinsics in a manner which is appropriate for the target collector.
These intrinsics allow identification of :ref:`GC roots on the
@ -7429,11 +7430,11 @@ Experimental Statepoint Intrinsics
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
LLVM provides an second experimental set of intrinsics for describing garbage
collection safepoints in compiled code. These intrinsics are an alternative
to the ``llvm.gcroot`` intrinsics, but are compatible with the ones for
:ref:`read <int_gcread>` and :ref:`write <int_gcwrite>` barriers. The
differences in approach are covered in the `Garbage Collection with LLVM
<GarbageCollection.html>`_ documentation. The intrinsics themselves are
collection safepoints in compiled code. These intrinsics are an alternative
to the ``llvm.gcroot`` intrinsics, but are compatible with the ones for
:ref:`read <int_gcread>` and :ref:`write <int_gcwrite>` barriers. The
differences in approach are covered in the `Garbage Collection with LLVM
<GarbageCollection.html>`_ documentation. The intrinsics themselves are
described in :doc:`Statepoints`.
.. _int_gcroot:
@ -9690,7 +9691,7 @@ The result of this operation is equivalent to a regular vector load instruction
::
%res = call <16 x float> @llvm.masked.load.v16f32 (<16 x float>* %ptr, i32 4, <16 x i1>%mask, <16 x float> %passthru)
;; The result of the two following instructions is identical aside from potential memory access exception
%loadlal = load <16 x float>, <16 x float>* %ptr, align 4
%res = select <16 x i1> %mask, <16 x float> %loadlal, <16 x float> %passthru
@ -9729,7 +9730,7 @@ The result of this operation is equivalent to a load-modify-store sequence. Howe
::
call void @llvm.masked.store.v16f32(<16 x float> %value, <16 x float>* %ptr, i32 4, <16 x i1> %mask)
;; The result of the following instructions is identical aside from potential data races and memory access exceptions
%oldval = load <16 x float>, <16 x float>* %ptr, align 4
%res = select <16 x i1> %mask, <16 x float> %value, <16 x float> %oldval