llvm-project

155dade8 - [bazel] Select Windows GNU BLAKE3 assembly for clang-cl (#217695)

[bazel] Select Windows GNU BLAKE3 assembly for clang-cl (#217695) ## Motivation This PR is motivated by ongoing work of providing a fully hermetic clang-cl bazel toolchain built for windows with the MSVC runtime. The LLVM Bazel overlay does not select a Windows-compatible BLAKE3 assembly source set for an x86_64 Windows target compiled with the rules_cc `clang-cl` compiler dialect. The `windows_gnu.S` name can be misleading here. "GNU" describes the assembly syntax accepted by GNU-style assemblers and Clang's integrated assembler; it does **not** mean that the implementation uses the MinGW ABI or runtime. These files implement the Microsoft x64 calling convention and are intended to produce Windows COFF objects. A hermetic clang-cl toolchain can therefore assemble the GNU-syntax Windows sources directly. Selecting the MASM-syntax `windows_msvc.asm` files instead would require a separately declared MASM tool such as `ml64.exe`, which this compiler route does not provide. LLVM's CMake build makes the same distinction indirectly: its `MSVC` branch first enables the separate `ASM_MASM` language and then selects `windows_msvc.asm`; its other Windows assembler branch selects `windows_gnu.S`. The MASM choice is therefore contingent on an available MASM assembler, not inherent to every compiler targeting the MSVC ABI. ## Tests - Compiled each selected `windows_gnu.S` file with LLVM clang-cl 22.1.8 targeting `x86_64-pc-windows-msvc`; all four outputs were AMD64 COFF objects and defined the expected SSE2, SSE4.1, AVX2, and AVX-512 BLAKE3 symbols. - Inspected the selected assembly: it uses the Microsoft x64 argument registers and preserves the required Windows-nonvolatile general-purpose and XMM registers. - Confirmed the corresponding `windows_msvc.asm` inputs are not accepted by this clang-cl-only route. They require a separately declared MASM assembler. - A downstream full x86_64 Windows LLVM build linked successfully with this source selection. The identical baseline reached the final link with undefined BLAKE3 SIMD dispatch symbols. Assisted by: codex