Allow custom default address spaces and parse `p-` specifications in the datalayout string #143182

xdoardo · 2025-06-29T10:17:45Z

Some targets, such as CHERI, use as default an address space different from the "normal" default address space 0 (in the case of CHERI, 200 is used). Currently, rustc does not allow to specify custom address spaces and does not take into consideration p- specifications in the datalayout string.

This patch tries to mitigate these problems by allowing targets to define a custom default address space (while keeping the default value to address space 0) and adding the code to parse the p- specifications in rustc_abi. The main changes are that TargetDataLayout now uses functions to refer to pointer-related informations, instead of having specific fields for the size and alignment of pointers in the default address space; furthermore, the two pointer_size and pointer_align fields in TargetDataLayout are replaced with an FxHashMap that holds info for all the possible address spaces, as parsed by the p- specifications.

The potential performance drawbacks of not having ad-hoc fields for the default address space will be tested in this PR's CI run.

r? workingjubilee

rustbot · 2025-06-29T10:17:50Z

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rustbot · 2025-06-29T10:17:52Z

Some changes occurred to the CTFE / Miri interpreter

cc @rust-lang/miri

These commits modify compiler targets.
(See the Target Tier Policy.)

Some changes occurred in compiler/rustc_ast_lowering/src/format.rs

cc @m-ou-se

Some changes occurred to the CTFE / Miri interpreter

cc @rust-lang/miri, @RalfJung, @oli-obk, @lcnr

Some changes occurred in cfg and check-cfg configuration

cc @Urgau

Some changes occurred to the CTFE machinery

cc @RalfJung, @oli-obk, @lcnr

Some changes occurred in compiler/rustc_codegen_ssa

cc @WaffleLapkin

workingjubilee · 2025-06-29T10:28:43Z

@bors2 try @rust-timer queue

rust-bors · 2025-06-29T10:28:47Z

⌛ Trying commit ef6e4ef with merge a6d8fc2…

To cancel the try build, run the command @bors2 try cancel.

Allow custom default address spaces and parse `p-` specifications in the datalayout string Some targets, such as CHERI, use as default an address space different from the "normal" default address space `0` (in the case of CHERI, [200 is used](https://www.cl.cam.ac.uk/techreports/UCAM-CL-TR-877.pdf)). Currently, `rustc` does not allow to specify custom address spaces and does not take into consideration [`p-` specifications in the datalayout string](https://llvm.org/docs/LangRef.html#langref-datalayout). This patch tries to mitigate these problems by allowing target to define a custom default address space (while keeping the default value to address space `0`) and adding the code to parse the `p-` specifications in `rustc_abi`. The main changes are that `TargetDataLayout` now uses functions to refer to pointer-related informations, instead of having specific fields for the size and alignment of pointers in the default address space: the potential performance drawbacks of not having ad-hoc fields will be tested in this PR's CI run. r? workingjubilee

rust-bors · 2025-06-29T12:47:13Z

☀️ Try build successful (CI)
Build commit: a6d8fc2 (a6d8fc279459764136b16847f5b4411d4298525d, parent: 5ca574e85b67cec0a6fc3fddfe398cbe676c9c69)

rust-timer · 2025-06-29T14:13:30Z

Finished benchmarking commit (a6d8fc2): comparison URL.

Overall result: ❌ regressions - please read the text below

Benchmarking this pull request means it may be perf-sensitive – we'll automatically label it not fit for rolling up. You can override this, but we strongly advise not to, due to possible changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please do so in sufficient writing along with @rustbot label: +perf-regression-triaged. If not, please fix the regressions and do another perf run. If its results are neutral or positive, the label will be automatically removed.

@bors rollup=never
@rustbot label: -S-waiting-on-perf +perf-regression

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	1.0%	[0.7%, 1.7%]	8
Regressions ❌ (secondary)	2.0%	[0.9%, 4.7%]	38
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	1.0%	[0.7%, 1.7%]	8

Max RSS (memory usage)

Results (primary -2.6%, secondary -8.0%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-2.6%	[-3.6%, -1.5%]	2
Improvements ✅ (secondary)	-8.0%	[-8.0%, -8.0%]	1
All ❌✅ (primary)	-2.6%	[-3.6%, -1.5%]	2

Cycles

Results (secondary 2.6%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	2.6%	[2.4%, 2.7%]	3
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 695.013s -> 695.668s (0.09%)
Artifact size: 371.77 MiB -> 372.01 MiB (0.06%)

rustbot · 2025-06-29T17:34:17Z

Some changes occurred in compiler/rustc_codegen_gcc

cc @antoyo, @GuillaumeGomez

rust-analyzer is developed in its own repository. If possible, consider making this change to rust-lang/rust-analyzer instead.

cc @rust-lang/rust-analyzer

Some changes occurred in compiler/rustc_codegen_cranelift

cc @bjorn3

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

workingjubilee · 2025-06-29T20:27:21Z

@bors2 try

rust-bors · 2025-06-29T20:27:25Z

⌛ Trying commit fce06e3 with merge 92687cf…

To cancel the try build, run the command @bors2 try cancel.

Allow custom default address spaces and parse `p-` specifications in the datalayout string Some targets, such as CHERI, use as default an address space different from the "normal" default address space `0` (in the case of CHERI, [200 is used](https://www.cl.cam.ac.uk/techreports/UCAM-CL-TR-877.pdf)). Currently, `rustc` does not allow to specify custom address spaces and does not take into consideration [`p-` specifications in the datalayout string](https://llvm.org/docs/LangRef.html#langref-datalayout). This patch tries to mitigate these problems by allowing targets to define a custom default address space (while keeping the default value to address space `0`) and adding the code to parse the `p-` specifications in `rustc_abi`. The main changes are that `TargetDataLayout` now uses functions to refer to pointer-related informations, instead of having specific fields for the size and alignment of pointers in the default address space; furthermore, the two `pointer_size` and `pointer_align` fields in `TargetDataLayout` are replaced with an `FxHashMap` that holds info for all the possible address spaces, as parsed by the `p-` specifications. The potential performance drawbacks of not having ad-hoc fields for the default address space will be tested in this PR's CI run. r? workingjubilee

rust-bors · 2025-06-29T22:43:09Z

☀️ Try build successful (CI)
Build commit: 92687cf (92687cf86ed4b58afb2653d78a1c735272295f02, parent: ed2d759783dc9de134bbb3f01085b1e6dbf539f3)

workingjubilee · 2025-06-30T06:53:02Z

@rust-timer build 92687cf

rust-timer · 2025-06-30T09:01:27Z

Finished benchmarking commit (92687cf): comparison URL.

Overall result: ❌ regressions - please read the text below

Benchmarking this pull request means it may be perf-sensitive – we'll automatically label it not fit for rolling up. You can override this, but we strongly advise not to, due to possible changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please do so in sufficient writing along with @rustbot label: +perf-regression-triaged. If not, please fix the regressions and do another perf run. If its results are neutral or positive, the label will be automatically removed.

@bors rollup=never
@rustbot label: -S-waiting-on-perf +perf-regression

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	0.4%	[0.4%, 0.6%]	4
Regressions ❌ (secondary)	1.1%	[0.3%, 1.9%]	29
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.4%	[0.4%, 0.6%]	4

Max RSS (memory usage)

Results (primary -2.3%, secondary 2.1%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	2.1%	[2.1%, 2.1%]	1
Improvements ✅ (primary)	-2.3%	[-3.1%, -1.4%]	2
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-2.3%	[-3.1%, -1.4%]	2

Cycles

Results (primary -1.1%, secondary 0.3%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	1.9%	[1.9%, 1.9%]	1
Improvements ✅ (primary)	-1.1%	[-1.2%, -0.9%]	2
Improvements ✅ (secondary)	-1.2%	[-1.2%, -1.2%]	1
All ❌✅ (primary)	-1.1%	[-1.2%, -0.9%]	2

Binary size

Results (secondary 0.0%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	0.0%	[0.0%, 0.0%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Bootstrap: 694.715s -> 695.8s (0.16%)
Artifact size: 371.77 MiB -> 371.86 MiB (0.02%)

…default data address space

…out`

rustbot assigned workingjubilee Jun 29, 2025

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rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Jun 29, 2025

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rustbot added perf-regression Performance regression. and removed S-waiting-on-perf Status: Waiting on a perf run to be completed. labels Jun 29, 2025

xdoardo force-pushed the more-addrspace branch from ef6e4ef to fce06e3 Compare June 29, 2025 17:34

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rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Jun 30, 2025

xdoardo added 2 commits June 30, 2025 17:40

Rename AddressSpace::DATA to AddressSpace::ZERO

7c550c4

compiler: Parse p- specs in datalayout string, allow definition of …

73aaf57

…default data address space

xdoardo force-pushed the more-addrspace branch from fce06e3 to defc7a8 Compare June 30, 2025 20:02

compiler: use vector instead of hashmap in rustc_abi's `TargetDataLay…

3f8b20b

…out`

xdoardo force-pushed the more-addrspace branch from defc7a8 to 3f8b20b Compare June 30, 2025 20:04

[squash later] ad-hoc fields for default_address_space_info

afec259

Allow custom default address spaces and parse p- specifications in the datalayout string #143182

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Allow custom default address spaces and parse p- specifications in the datalayout string #143182

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Overall result: ❌ regressions - please read the text below

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Overall result: ❌ regressions - please read the text below

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Allow custom default address spaces and parse `p-` specifications in the datalayout string #143182

Allow custom default address spaces and parse `p-` specifications in the datalayout string #143182

xdoardo commented Jun 29, 2025 •

edited

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