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Differential D116077

[AMDGPU][NFC] Update DWARF extension for locations on the stack
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Authored by t-tye on Dec 20 2021, 8:55 PM.

Details

Reviewers
kzhuravl
scott.linder
Commits
rG0a3258febf2f: [AMDGPU][NFC] Update DWARF extension for locations on the stack
Summary
  • Improve extension description.
  • Rename "What is DWARF?" section to better reflect what it is describing.

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Event Timeline

t-tye created this revision.Dec 20 2021, 8:55 PM
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t-tye requested review of this revision.Dec 20 2021, 8:55 PM
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kzhuravl accepted this revision.Dec 20 2021, 9:10 PM
This revision is now accepted and ready to land.Dec 20 2021, 9:10 PM
Harbormaster completed remote builds in B140184: Diff 395583.Dec 20 2021, 9:49 PM
This revision was landed with ongoing or failed builds.Dec 20 2021, 9:58 PM
Closed by commit rG0a3258febf2f: [AMDGPU][NFC] Update DWARF extension for locations on the stack (authored by t-tye). · Explain Why
This revision was automatically updated to reflect the committed changes.
t-tye added a commit: rG0a3258febf2f: [AMDGPU][NFC] Update DWARF extension for locations on the stack.

Revision Contents

PathSize
llvm/
docs/
AMDGPUDwarfExtensionAllowLocationDescriptionOnTheDwarfExpressionStack/
29 lines

Diff 395594

llvm/docs/AMDGPUDwarfExtensionAllowLocationDescriptionOnTheDwarfExpressionStack/AMDGPUDwarfExtensionAllowLocationDescriptionOnTheDwarfExpressionStack.md

# Allow Location Descriptions on the DWARF Expression Stack <!-- omit in toc --> # Allow Location Descriptions on the DWARF Expression Stack <!-- omit in toc -->
- [Extension](#extension) - [Extension](#extension)
- [Heterogeneous Computing Devices](#heterogeneous-computing-devices) - [Heterogeneous Computing Devices](#heterogeneous-computing-devices)
- [DWARF 5](#dwarf-5) - [DWARF 5](#dwarf-5)
- [What is DWARF?](#what-is-dwarf) - [How DWARF Maps Source Language To Hardware](#how-dwarf-maps-source-language-to-hardware)
- [Examples](#examples) - [Examples](#examples)
- [Dynamic Array Size](#dynamic-array-size) - [Dynamic Array Size](#dynamic-array-size)
- [Variable Location in Register](#variable-location-in-register) - [Variable Location in Register](#variable-location-in-register)
- [Variable Location in Memory](#variable-location-in-memory) - [Variable Location in Memory](#variable-location-in-memory)
- [Variable Spread Across Different Locations](#variable-spread-across-different-locations) - [Variable Spread Across Different Locations](#variable-spread-across-different-locations)
- [Offsetting a Composite Location](#offsetting-a-composite-location) - [Offsetting a Composite Location](#offsetting-a-composite-location)
- [Limitations](#limitations) - [Limitations](#limitations)
- [Extension Solution](#extension-solution) - [Extension Solution](#extension-solution)
Show All 9 Lines- [Extension Solution](#extension-solution)
- [Objects Not In Byte Aligned Global Memory](#objects-not-in-byte-aligned-global-memory) - [Objects Not In Byte Aligned Global Memory](#objects-not-in-byte-aligned-global-memory)
- [Higher Order Operations](#higher-order-operations) - [Higher Order Operations](#higher-order-operations)
- [Objects In Multiple Places](#objects-in-multiple-places) - [Objects In Multiple Places](#objects-in-multiple-places)
- [Conclusion](#conclusion) - [Conclusion](#conclusion)
- [Further Information](#further-information) - [Further Information](#further-information)
# Extension # Extension
This extension is to generalize the DWARF expression evaluation model to allow In DWARF 5, expressions are evaluated using a typed value stack, a separate
location descriptions to be manipulated on the stack. It is done in a manner location area, and an independent loclist mechanism. This extension unifies all
that is backwards compatible with DWARF 5. This permits operations to act on three mechanisms into a single generalized DWARF expression evaluation model
location descriptions in an incremental, consistent, and composable manner. that allows both typed values and location descriptions to be manipulated on the
evaluation stack. Both single and multiple location descriptions are supported
It allows a small number of operations to be defined to address the requirements on the stack. In addition, the call frame information (CFI) is extended to
of heterogeneous devices as well as providing benefits to non-heterogeneous support the full generality of location descriptions. This is done in a manner
devices. It also acts as a foundation to provide support for other issues that that is backwards compatible with DWARF 5. The extension involves changes to the
have been raised that would benefit all devices. DWARF 5 sections 2.5 (pp 26-38), 2.6 (pp 38-45), and 6.4 (pp 171-182).
The extension permits operations to act on location descriptions in an
incremental, consistent, and composable manner. It allows a small number of
operations to be defined to address the requirements of heterogeneous devices as
well as providing benefits to non-heterogeneous devices. It acts as a foundation
to provide support for other issues that have been raised that would benefit all
devices.
Other approaches were explored that involved adding specialized operations and Other approaches were explored that involved adding specialized operations and
rules. However, these resulted in the need for more operations that did not rules. However, these resulted in the need for more operations that did not
compose. It also resulted in operations with context sensitive semantics and compose. It also resulted in operations with context sensitive semantics and
corner cases that had to be defined. The observation was that numerous corner cases that had to be defined. The observation was that numerous
specialized context sensitive operations are harder for both produces and specialized context sensitive operations are harder for both produces and
consumers than a smaller number of general composable operations that have consumers than a smaller number of general composable operations that have
consistent semantics regardless of context. consistent semantics regardless of context.
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location kinds to be supported uniformly, otherwise duplication is necessary. location kinds to be supported uniformly, otherwise duplication is necessary.
# DWARF 5 # DWARF 5
Before presenting the proposed solution to supporting heterogeneous devices, a Before presenting the proposed solution to supporting heterogeneous devices, a
brief overview of the DWARF 5 expression evaluation model will be given to brief overview of the DWARF 5 expression evaluation model will be given to
highlight the aspects being addressed by the extension. highlight the aspects being addressed by the extension.
## What is DWARF? ## How DWARF Maps Source Language To Hardware
DWARF is a standardized way to specify debug information. It describes source DWARF is a standardized way to specify debug information. It describes source
language entities such as compilation units, functions, types, variables, etc. language entities such as compilation units, functions, types, variables, etc.
It is either embedded directly in sections of the code object executables, or It is either embedded directly in sections of the code object executables, or
split into separate files that they reference. split into separate files that they reference.
DWARF maps between source program language entities and their hardware DWARF maps between source program language entities and their hardware
representations. For example: representations. For example:
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