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022-memory-spaces.txt
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022-memory-spaces.txt
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Part 18: Support for Source Language Memory Spaces
PROBLEM DESCRIPTION
AMDGPU supports languages, such as OpenCL, that define source language memory
classes. Support is added to define language specific memory spaces so they can
be used in a consistent way by consumers.
A new attribute DW_AT_memory_space is added to support using memory spaces in
defining source language pointer and reference types and data object
allocation.
PROPOSAL
In Section 2.2 "Attribute Types", add the following row to Table 2.2 "Attribute
names":
----------------------------------------------------------------------------
Table 2.2: Attribute names
=========================== ====================================
Attribute Usage
=========================== ====================================
DW_AT_memory_space Pointer or reference types (see 5.3 "Type Modifier Entries")
Data objects (see 4.1 "Data Object Entries")
=========================== ====================================
Add the following after Section 2.12 "Segmented Addresses":
----------------------------------------------------------------------------
2.x Memory Spaces
DWARF memory spaces are used for source languages that have the concept of
memory spaces. They are used in the DW_AT_memory_space attribute for pointer
type, reference type, variable, formal parameter, and constant debugger
information entries.
Each DWARF memory space is conceptually a separate source language memory
space with its own lifetime and aliasing rules. DWARF memory spaces are used
to specify the source language memory spaces that pointer type and reference
type values refer, and to specify the source language memory space in which
variables are allocated.
Although DWARF memory space identifiers are source language specific,
DW_MSPACE_none is a common memory space supported by all source languages,
and defined as the source language default memory space.
The set of currently defined DWARF memory spaces, together with source
language mappings, is given in Table 2.x "Source language memory space".
Vendor defined source language memory spaces may be defined using codes in
the range DW_MSPACE_lo_user to DW_MSPACE_hi_user.
Table 2.x: Source language memory spaces
================== ============ ============== ============== ==============
Memory Space Name Meaning C/C++ OpenCL CUDA/HIP
================== ============ ============== ============== ==============
DW_MSPACE_none generic <i>default</i> generic <i>default</i>
DW_MSPACE_global global global
DW_MSPACE_constant constant constant constant
DW_MSPACE_group thread-group local shared
DW_MSPACE_private thread private
DW_MSPACE_lo_user
DW_MSPACE_hi_user
================== ============ ============== ============== ==============
----------------------------------------------------------------------------
> [For further discussion...]
> The approach presented in Table 2.x "Source language memory spaces" is to
> define the default DW_MSPACE_none to be the generic address class and not the
> global address class. This matches how CLANG and LLVM have added support for
> CUDA-like languages on top of existing C++ language support. This allows all
> addresses to be generic by default which matches CUDA-like languages.
>
> An alternative approach is to define DW_MSPACE_none as being the global memory
> space and then change DW_MSPACE_global to DW_MSPACE_generic. This would match
> the reality that languages that do not support multiple memory spaces only
> have one default global memory space. Generally, in these languages if they
> expose that the target architecture supports multiple memory spaces, the
> default one is still the global memory space. Then a language that does
> support multiple memory spaces has to explicitly indicate which pointers have
> the added ability to reference more than the global memory space. However,
> compilers generating DWARF for CUDA-like languages would then have to define
> every CUDA-like language pointer type or reference type with a
> DW_AT_memory_space attribute of DW_MSPACE_generic to match the language
> semantics.
In Section 4.1 "Data Object Entries" add the following to the attribute list:
----------------------------------------------------------------------------
14. A DW_AT_memory_space attribute with a constant value representing a
source language specific DWARF memory space (see 2.x "Memory Spaces").
If omitted, defaults to DW_MSPACE_none.
----------------------------------------------------------------------------
In Section 5.3 "Type Modifier Entries", after the paragraph starting "A modified
type entry describing a pointer or reference type...", add the following
paragraph:
----------------------------------------------------------------------------
A modified type entry describing a pointer or reference type (using
DW_TAG_pointer_type, DW_TAG_reference_type or DW_TAG_rvalue_reference_type)
may have a DW_AT_memory_space attribute with a constant value representing a
source language specific DWARF memory space (see 2.x "Memory Spaces"). If
omitted, defaults to DW_MSPACE_none.
----------------------------------------------------------------------------
In Section 7.5.4 "Attribute Encodings", add the following row to Table 7.5
"Attribute encodings":
----------------------------------------------------------------------------
Table 7.5: Attribute encodings
================================== ====== ==================================
Attribute Name Value Classes
================================== ====== ==================================
DW_AT_memory_space TBA constant
================================== ====== ==================================
----------------------------------------------------------------------------
After Section 7.13 "Address Class Encodings" and Section 7.x "Address Space
Encodings", add the following section:
----------------------------------------------------------------------------
7.x Memory Space Encodings
The encodings of the constants used for the currently defined memory spaces
are given in Table 7.x "Memory space encodings".
Table 7.x: Memory space encodings
========================== ======
Memory Space Name Value
========================== ======
DW_MSPACE_none 0x0000
DW_MSPACE_global 0x0001
DW_MSPACE_constant 0x0002
DW_MSPACE_group 0x0003
DW_MSPACE_private 0x0004
DW_MSPACE_lo_user 0x8000
DW_MSPACE_hi_user 0xffff
========================== ======
----------------------------------------------------------------------------
In Section 7.32 "Type Signature Computation", Table 7.32 "Attributes used in
type signature computation", add the following attribute in alphabetical order
to the list:
----------------------------------------------------------------------------
DW_AT_memory_space
----------------------------------------------------------------------------
In Appendix A "Attributes by Tag Value (Informative)", add the following to
Table A.1 Attributes by tag value":
----------------------------------------------------------------------------
Table A.1: Attributes by tag value
============================= =============================
Tag Name Applicable Attributes
============================= =============================
DW_TAG_variable DW_AT_memory_space
DW_TAG_formal_parameter DW_AT_memory_space
DW_TAG_constant DW_AT_memory_space
DW_TAG_pointer_type DW_AT_memory_space
DW_TAG_reference_type DW_AT_memory_space
DW_TAG_rvalue_reference_type DW_AT_memory_space
============================= =============================