[all-commits] [llvm/llvm-project] 333edd: [BPF] Return small aggregates directly in register...

[yonghong-song via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: 333edde4e80e02d6fe5e866abf317969b66c0b8e
      https://github.com/llvm/llvm-project/commit/333edde4e80e02d6fe5e866abf317969b66c0b8e
  Author: yonghong-song <yhs at fb.com>
  Date:   2026-07-07 (Tue, 07 Jul 2026)

  Changed paths:
    M clang/lib/CodeGen/Targets/BPF.cpp
    A clang/test/CodeGen/bpf-struct-return-regs.c
    A clang/test/CodeGen/bpf-struct-return.c
    A llvm/test/CodeGen/BPF/aggr_ret_regs.ll

  Log Message:
  -----------
  [BPF] Return small aggregates directly in registers (#206876)

Previously the BPF ABI always returned aggregate (struct/union) types
indirectly through an sret pointer, regardless of size. This is
inconsistent with how classifyArgumentType() already passes small
aggregates: arguments up to 128 bits are coerced into one or two 64-bit
registers, while only larger aggregates use an indirect reference.

Make classifyReturnType() mirror that convention by factoring the shared
aggregate handling into a classifyAggregateType() helper used by both:

  - empty aggregates (0 bits) are ignored;
- aggregates up to 64 bits are returned directly, coerced to an integer
of the padded size;
  - aggregates of 65..128 bits are returned directly as [2 x i64];
  - aggregates larger than 128 bits are returned indirectly via sret.

This keeps each returned value within the backend's two-register return
convention and avoids an unnecessary memory round-trip for small
structs.

This also aligns BPF with the general-purpose C ABIs of other targets:
both x86-64 (System V, RAX:RDX) and AArch64 (AAPCS64, X0:X1) return
aggregates up to 16 bytes in a pair of registers and only fall back to
an indirect sret pointer for larger ones.

Co-authored-by: Yonghong Song <yonghong.song at linux.dev>



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