[all-commits] [llvm/llvm-project] da816c: [TTI][BPF] Ensure ArgumentPromotion Not Exceeding ...

[yonghong-song via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: da816c2985263f108e852adc99c31b6775096010
      https://github.com/llvm/llvm-project/commit/da816c2985263f108e852adc99c31b6775096010
  Author: Yonghong Song <yhs at fb.com>
  Date:   2023-04-19 (Wed, 19 Apr 2023)

  Changed paths:
    M llvm/include/llvm/Analysis/TargetTransformInfo.h
    M llvm/include/llvm/Analysis/TargetTransformInfoImpl.h
    M llvm/lib/Analysis/TargetTransformInfo.cpp
    M llvm/lib/Target/BPF/BPFTargetTransformInfo.h
    M llvm/lib/Transforms/IPO/ArgumentPromotion.cpp
    A llvm/test/Transforms/ArgumentPromotion/BPF/argpromotion.ll
    A llvm/test/Transforms/ArgumentPromotion/BPF/lit.local.cfg

  Log Message:
  -----------
  [TTI][BPF] Ensure ArgumentPromotion Not Exceeding Target MaxArgs

With LLVM patch https://reviews.llvm.org/D148269, we hit a linux kernel
bpf selftest compilation failure like below:
  ...
  progs/test_xdp_noinline.c:739:8: error: too many args to t8: i64 = GlobalAddress<ptr @encap_v4> 0, progs/test_xdp_noinline.c:739:8
              if (!encap_v4(xdp, cval, &pckt, dst, pkt_bytes))
                   ^
  ...
  progs/test_xdp_noinline.c:321:6: error: defined with too many args
  bool encap_v4(struct xdp_md *xdp, struct ctl_value *cval,
       ^
  ...

Note that bpf selftests are compiled with -O2 which is
the recommended flag for bpf community.

The bpf backend calling convention is only allowing 5
parameters in registers and does not allow pass arguments
through stacks. In the above case, ArgumentPromotionPass
replaced parameter '&pckt' as two parameters, so the total
number of arguments after ArgumentPromotion pass becomes 6
and this caused later compilation failure during instruction
selection phase.

This patch added a TargetTransformInfo hook getMaxNumArgs()
which returns 5 for BPF and UINT_MAX for other targets.

Differential Revision: https://reviews.llvm.org/D148551