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feat(cuda-oxide): lower libm lgamma_r through libdevice - #1652

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uurl wants to merge 7 commits into
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uurl:feat/libdevice-lgamma-r

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@uurl

@uurl uurl commented Oct 26, 2026 •

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Summary

  • Add generated mappings for libm::lgamma_r and libm::lgammaf_r, bringing coverage to 110 of 124 f32/f64 exports.
  • Compose libm's (log(abs(gamma(x))), signgam) tuple from the existing validated libdevice lgamma, floor, and fmod symbols. Handle negative intervals, integer poles, signed zero, and infinities.
  • Add compiler tests for both backends, tuple layouts, and invalid signatures, plus a CUDA example comparing both precisions against libm.

Validation

  • cargo run -p cuda-intrinsics-gen --locked -- check
  • cargo test -p cuda-intrinsics-gen -p dialect-mir -p mir-importer -p mir-lower --all-targets --locked
  • cargo clippy -p cuda-intrinsics-gen -p dialect-mir -p mir-importer -p mir-lower --all-targets --locked -- -D warnings
  • cargo oxide run math_lgamma_r: 208 checks passed across f32 and f64
  • just check: passed

Depends on #1651. Part of #1224; the remaining 14 exports are outside this PR.

Testing

  • just -f cuda-oxide/Justfile check passes (the local mirror of CI: fmt, clippy, tests, guards, docs)
  • cargo oxide run <example> passes, or cuda-oxide/scripts/smoketest.sh -o '^<example>$'
  • New example added

Checklist

  • All commits signed off (git commit -s)
  • SPDX headers on new source files

uurl added 7 commits October 25, 2026 19:16
Signed-off-by: Raul Estrada <raulestradaa@gmail.com>
Signed-off-by: Raul Estrada <raulestradaa@gmail.com>
Signed-off-by: Raul Estrada <raulestradaa@gmail.com>
Signed-off-by: Raul Estrada <raulestradaa@gmail.com>
Signed-off-by: Raul Estrada <raulestradaa@gmail.com>
Signed-off-by: Raul Estrada <raulestradaa@gmail.com>
Signed-off-by: Raul Estrada <raulestradaa@gmail.com>
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@uurl
uurl marked this pull request as ready for review October 26, 2026 06:56
@uurl
uurl requested a review from nihalpasham as a code owner October 26, 2026 06:56
@nihalpasham nihalpasham added the cuda-oxide SIMT programming model: rustc backend, cargo oxide, cuda-device, cuda-host, book label Oct 29, 2026
@nihalpasham

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Thanks! Since #1660 contains the full 9-commit #1224 stack in linear order (including this commit with your authorship preserved), I am landing the entire series together through #1660 and closing this intermediate stack PR.

nihalpasham added a commit that referenced this pull request Oct 29, 2026
…120 libm exports (#1660)

## What This PR Does

Implements `#1224` across the 9-commit `libdevice_math` series (`#1638`,
`#1645`, `#1646`, `#1649`, `#1650`, `#1651`, `#1652`, `#1653`, `#1660`),
replacing hand-maintained math dispatch tables across three crates with
a single generated table backed by `libdevice.10.bc` evidence and
expanding `libm 0.2.16` coverage from 72 to **120 of 124 `f32`/`f64`
exports**:

1. **Add `intrinsics/overlay/libdevice_math.toml` + `libdevice.10.bc`
signature verification and generate `dialect-mir` math dispatch
(`cuda-intrinsics-gen`, `dialect-mir`, `mir-importer`,
`rustc-codegen-cuda`)**
2. **Extract float-math lowering into
`mir-lower/src/convert/ops/float_math.rs` driven by generated
`RustFloatMathLowering` (`mir-lower`)**
3. **Lower scalar aliases (`tgamma`, `ilogb`, `ldexp`, `erf`, `j0`,
`y0`, ...), entry-block out-parameter adapters (`frexp`, `modf`,
`remquo`), `lgamma_r`, C23 `fmaximum`/`fminimum`, and `j1` (`mir-lower`,
`examples/math_special`)**

---

### 1. Generated `libm -> libdevice` Dispatch (`#1224`)

Previously, wiring a single `libm` or `std::sys::cmath` function
required hand-editing ~10 sites across
`rustc-codegen-cuda/src/collector.rs`, `mir-importer`, `dialect-mir`,
and `mir-lower`:

```text
BEFORE (hand-maintained across 4 crates):
  collector.rs       ──► hardcoded `std::sys::cmath::*` match list
  mir-importer       ──► hand-written `RustFloatMathIntrinsic` enum + `from_core_path` / `from_libm_path`
  dialect-mir        ──► hand-written `CALLEE_*` constants + `is_libdevice_backed_placeholder`
  mir-lower          ──► hand-written placeholder -> `__nv_*` match table

AFTER (`intrinsics/overlay/libdevice_math.toml` -> `cuda-intrinsics-gen`):
  libdevice_math.toml + cuda-13.0.json (102 signatures verified against libdevice.10.bc)
    │
    ▼
  crates/dialect-mir/src/generated/libdevice_math.rs
    ├──► collector.rs   `is_intrinsic_lowered_cmath_shim(fn_path)`
    ├──► mir-importer   `from_core_path` + `from_libm_path` -> `CALLEE_*`
    ├──► codegen        `link_requirement()` -> `MathLink::{Always, Libnvvm, Never}`
    └──► mir-lower      `RustFloatMathIntrinsic::lowering(self) -> RustFloatMathLowering`
```

---

### 2. Entry-Block Out-Parameter Adapters & IEEE Edge-Case Lowerings
(`mir-lower`)

```text
Function Family                Lowering in `mir-lower/src/convert/ops/float_math.rs`
─────────────────────────────  ──────────────────────────────────────────────────────────────────────────
`frexp`, `modf`, `remquo`      Hoists `llvm.alloca` to function entry block (`0` `.local` traffic after
                               `opt -O2` SROA); normalizes `frexp(+-inf/NaN) -> (x, 0)` and `remquo` NaN -> `quo = 0`
`lgamma_r`, `lgammaf_r`        Composes `__nv_lgamma`, `__nv_floor`, and `__nv_fmod(floor(x), 2.0)` with
                               `-0.0 -> (+inf, -1)`, negative integer poles `-> (+inf, +1)`, `-inf -> (+inf, +1)`
C23 `fmaximum*` / `fminimum*`  Pure LLVM `fcmp` (empty fast-math flags) + sign-bit tie-break (`-0.0 < +0.0`)
`j1`, `j1f`                    Calls `__nv_j1{,f}` and normalizes `|x| == inf -> +0.0`
```

---

## Verification

* **RTX 5090 (`sm_120a`) GPU Execution & Sanitizer**:
* `cargo oxide run math_special`: **2,822 / 2,822 `f32` and `f64` checks
PASS** (`compute-sanitizer --tool memcheck`: `0 errors`, `0` `.local`
instructions emitted for `frexp`, `modf`, `remquo`, `lgamma_r`, and C23
`minmax`).
* `cargo oxide run libm_math` & `cargo oxide run libdevice_math`:
**PASS**.
* **Generator & Bitcode Verification**:
* `cargo run -p cuda-intrinsics-gen -- check` & `verify-libdevice`:
**PASS** (`102` `libdevice.10.bc` signatures verified).
* **Tests, Lints & Guards**:
* `cargo test -p cuda-intrinsics-gen -p dialect-mir -p mir-importer -p
mir-lower -p cuda-oxide-codegen --all-targets`: **3,494 tests PASS**
* `just fmt-check`, `just clippy`, `scripts/sync-example-locks.sh
--check`, and all 18 `scripts/check-*.sh` guards: **all PASS**

Closes #1224

---------

Signed-off-by: Raul Estrada <raulestradaa@gmail.com>
Signed-off-by: nihalpasham <nihalp@nvidia.com>
Co-authored-by: nihalpasham <nihalp@nvidia.com>
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