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Implememting named register intrinsics

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This patch implements the infrastructure to use named register constructs in
programs that need access to specific registers (bare metal, kernels, etc).

So far, only the stack pointer is supported as a technology preview, but as it
is, the intrinsic can already support all non-allocatable registers from any
architecture.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208104 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Renato Golin
2014-05-06 16:51:25 +00:00
parent b889448841
commit 22f779d1fd
29 changed files with 376 additions and 0 deletions
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45
docs/LangRef.rst
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@@ -6804,6 +6804,51 @@ Note that calling this intrinsic does not prevent function inlining or
other aggressive transformations, so the value returned may not be that
of the obvious source-language caller.
.. _int_read_register:
.. _int_write_register:
'``llvm.read_register``' and '``llvm.write_register``' Intrinsics
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Syntax:
"""""""
::
declare i32 @llvm.read_register.i32(metadata)
declare i64 @llvm.read_register.i64(metadata)
declare void @llvm.write_register.i32(metadata, i32 @value)
declare void @llvm.write_register.i64(metadata, i64 @value)
!0 = metadata !{metadata !"sp\00"}
Overview:
"""""""""
The '``llvm.read_register``' and '``llvm.write_register``' intrinsics
provides access to the named register. The register must be valid on
the architecture being compiled to. The type needs to be compatible
with the register being read.
Semantics:
""""""""""
The '``llvm.read_register``' intrinsic returns the current value of the
register, where possible. The '``llvm.write_register``' intrinsic sets
the current value of the register, where possible.
This is useful to implement named register global variables that need
to always be mapped to a specific register, as is common practice on
bare-metal programs including OS kernels.
The compiler doesn't check for register availability or use of the used
register in surrounding code, including inline assembly. Because of that,
allocatable registers are not supported.
Warning: So far it only works with the stack pointer on selected
architectures (ARM, ARM64, x86_64 and AArch64). Significant amount of
work is needed to support other registers and even more so, allocatable
registers.
.. _int_stacksave:
'``llvm.stacksave``' Intrinsic