Basic inline assembly support for SPARC and SPARC64 #132472

taiki-e · 2024-11-01T19:18:53Z

This implements asm_experimental_arch (tracking issue #93335) for SPARC and SPARC64.

This PR includes:

General-purpose registers r[0-31] (reg register class, LLVM/GCC constraint r)
Supported types: i8, i16, i32, i64 (SPARC64-only)
Aliases: g[0-7] (r[0-7]), o[0-7] (r[8-15]), l[0-7] (r[16-23]), i[0-7] (r[24-31])
y register (clobber-only, needed for clobber_abi)
preserves_flags: Integer condition codes (icc, xcc) and floating-point condition codes (fcc*)

The following are not included:

64-bit integer support on SPARC-V8+'s global or out registers (g[0-7], o[0-7]): GCC's h constraint (it seems that there is no corresponding constraint in LLVM?)
Floating-point registers (LLVM/GCC constraint e/f):
I initially tried to implement this, but postponed it for now because there seemed to be several parts in LLVM that behaved differently than in the LangRef's description.
clobber_abi: Support for floating-point registers is needed.

Refs:

LLVM
- Reserved registers https://github.com/llvm/llvm-project/blob/llvmorg-19.1.0/llvm/lib/Target/Sparc/SparcRegisterInfo.cpp#L52
- Register definitions https://github.com/llvm/llvm-project/blob/llvmorg-19.1.0/llvm/lib/Target/Sparc/SparcRegisterInfo.td
- Supported constraints https://llvm.org/docs/LangRef.html#supported-constraint-code-list
GCC
- Reserved registers https://github.com/gcc-mirror/gcc/blob/63b6967b06b5387821c4e5f2c113da6aaeeae2b7/gcc/config/sparc/sparc.h#L633-L658
- Supported constraints https://gcc.gnu.org/onlinedocs/gcc/Machine-Constraints.html
SPARC ISA/ABI
- (64-bit ISA) The SPARC Architecture Manual, Version 9
  (32-bit ISA) The SPARC Architecture Manual, Version 8
  (64-bit ABI) System V Application Binary Interface SPARC Version 9 Processor Supplement, Rev 1.35
  (32-bit ABI) System V Application Binary Interface SPARC Processor Supplement, Third Edition
  The above docs can be downloaded from https://sparc.org/technical-documents
- (32-bit V8+ ABI) The V8+ Technical Specification
  https://temlib.org/pub/SparcStation/Standards/V8plus.pdf

cc @thejpster (sparc-unknown-none-elf target maintainer)
(AFAIK, other sparc/sprac64 targets don't have target maintainers)

r? @Amanieu

@rustbot label +O-SPARC +A-inline-assembly

rustbot · 2024-11-01T19:19:03Z

Some changes occurred in compiler/rustc_codegen_gcc

cc @antoyo, @GuillaumeGomez

compiler/rustc_target/src/asm/sparc.rs

taiki-e · 2024-11-01T19:52:23Z

/checkout/tests/ui/asm/bad-arch.rs: revision [unspecified] should specify needs-llvm-components: as it has --target set

Hmm, but when I set needs-llvm-components, I got:

/checkout/tests/ui/asm/bad-arch.rs: revision [unspecified] specifies unknown LLVM component xtensa

IIUC, it seems difficult to retain this test since there is no builtin target other than xtensa that does not support inline assembly in rust-lang/rust after this PR, and xtensa can probably support inline assembly in LLVM 20 (llvm/llvm-project@dc2d0d5, inline assembly itself is already supported in esp-rs fork).

UPDATE: removed this test

bors · 2024-11-05T19:51:55Z

☔ The latest upstream changes (presumably #129884) made this pull request unmergeable. Please resolve the merge conflicts.

Amanieu · 2024-11-06T22:40:25Z

src/doc/unstable-book/src/language-features/asm-experimental-arch.md

+| SPARC        | `r0`/`g0`                               | This is always zero and cannot be used as inputs or outputs. |
+| SPARC        | `r1`/`g1`                               | Used internally by LLVM. |
+| SPARC        | `r6`/`g6`, `r7`/`g7`                    | Reserved for system. |
+| SPARC        | `r31`/`i7`                              | Return address cannot be used as inputs or outputs. |


i6/o6 also need to be added to the list of stack/frame pointers.

And g5 needs to be mentioned as reserved on sparc32.

Good catch! I have updated docs to mention them.

Amanieu · 2024-11-06T22:41:42Z

compiler/rustc_target/src/asm/sparc.rs

+    ) -> &'static [(InlineAsmType, Option<Symbol>)] {
+        match self {
+            Self::reg => {
+                // FIXME: i64 is ok for g*/o* registers on SPARC-V8+ ("h" constraint in GCC)


This is better expressed as "v9": I64 in the macro. The feature name can later be changed to v8plus.

That constraint is not yet supported in LLVM, so I have updated the FIXME comment to use the way you mention.

rust/compiler/rustc_target/src/asm/sparc.rs

Lines 44 to 49 in 241f82a

types! {

_: I8, I16, I32;

// FIXME: i64 is ok for g*/o* registers on SPARC-V8+ ("h" constraint in GCC),

// but not yet supported in LLVM.

// v8plus: I64;

}

Amanieu · 2024-11-06T22:43:01Z

compiler/rustc_target/src/asm/sparc.rs

+    _target: &Target,
+    _is_clobber: bool,
+) -> Result<(), &'static str> {
+    if is_v7_or_v8(arch, target_features) {


The condition used in LLVM is Subtarget.is64Bit(), not whether v8plus is supported. So this should check for InlineAsmArch::Sparc64 instead.

Hmm. Section 2.1.5 "Function Registers with Unassigned Roles" of the V8+ Technical Specification says "%g5; no longer reserved for system software" 1, and LLVM does not seem to match it.

I have changed the condition to Sparc64 vs Sparc and left a FIXME comment mentioning the mismatch between LLVM and the specification.

(The above change removes the need for the addition of the target feature in this PR. It is still needed for other purposes but will be handled in another PR: #132552)

Amanieu · 2024-11-07T13:04:12Z

I would expect all the FIXME to be resolved before stabilization, but this is good enough for nightly.

@bors r+

bors · 2024-11-07T13:04:15Z

📌 Commit 241f82a has been approved by Amanieu

It is now in the queue for this repository.

matthiaskrgr · 2024-11-07T17:20:15Z

@bors rollup=iffy

bors · 2024-11-07T21:07:10Z

⌛ Testing commit 241f82a with merge b91a3a0...

bors · 2024-11-07T23:34:24Z

☀️ Test successful - checks-actions
Approved by: Amanieu
Pushing b91a3a0 to master...

rust-timer · 2024-11-08T00:51:22Z

Finished benchmarking commit (b91a3a0): comparison URL.

Overall result: ❌ regressions - no action needed

@rustbot label: -perf-regression

Instruction count

This is the most reliable metric that we have; it was used to determine the overall result at the top of this comment. However, even this metric can sometimes exhibit noise.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	0.8%	[0.8%, 0.8%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (primary -0.7%, secondary -1.9%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	1.3%	[1.3%, 1.3%]	1
Regressions ❌ (secondary)	2.2%	[2.2%, 2.2%]	1
Improvements ✅ (primary)	-2.7%	[-2.7%, -2.7%]	1
Improvements ✅ (secondary)	-2.9%	[-4.4%, -2.1%]	4
All ❌✅ (primary)	-0.7%	[-2.7%, 1.3%]	2

Cycles

Results (primary 2.3%, secondary 7.5%)

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	2.3%	[2.3%, 2.3%]	1
Regressions ❌ (secondary)	7.5%	[6.7%, 8.2%]	4
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	2.3%	[2.3%, 2.3%]	1

Binary size

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

Bootstrap: 780.698s -> 781.906s (0.15%)
Artifact size: 335.29 MiB -> 335.33 MiB (0.01%)

rustbot assigned Amanieu Nov 1, 2024

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Nov 1, 2024

rustbot added A-inline-assembly Area: Inline assembly (`asm!(…)`) O-SPARC Target: SPARC processors labels Nov 1, 2024

taiki-e mentioned this pull request Nov 1, 2024

Tracking Issue for asm_experimental_arch #93335

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taiki-e commented Nov 1, 2024

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taiki-e mentioned this pull request Nov 1, 2024

Support SPARC and SPARC64 (experimental) taiki-e/atomic-maybe-uninit#31

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This was referenced Nov 3, 2024

Support clobber_abi in AVR inline assembly #131323

Open

Add v9, v8plus, and leoncasa target feature to sparc and use v8plus in create_object_file #132552

Open

Generate correct symbols.o for sparc-unknown-none-elf #131222

Merged

Amanieu reviewed Nov 6, 2024

View reviewed changes

Basic inline assembly support for SPARC and SPARC64

241f82a

taiki-e force-pushed the sparc-asm branch from 58769e6 to 241f82a Compare November 7, 2024 12:19

bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Nov 7, 2024

bors added the merged-by-bors This PR was explicitly merged by bors. label Nov 7, 2024

bors merged commit b91a3a0 into rust-lang:master Nov 7, 2024
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rustbot added this to the 1.84.0 milestone Nov 7, 2024

This was referenced Nov 8, 2024

Stabilize s390x inline assembly #131258

Open

Stabilize Arm64EC inline assembly #131781

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taiki-e deleted the sparc-asm branch November 8, 2024 01:39

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Basic inline assembly support for SPARC and SPARC64 #132472

Basic inline assembly support for SPARC and SPARC64 #132472

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rust-timer commented Nov 8, 2024

	types! {
	_: I8, I16, I32;
	// FIXME: i64 is ok for g/o registers on SPARC-V8+ ("h" constraint in GCC),
	// but not yet supported in LLVM.
	// v8plus: I64;
	}

Basic inline assembly support for SPARC and SPARC64 #132472

Basic inline assembly support for SPARC and SPARC64 #132472

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Overall result: ❌ regressions - no action needed

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