Re: [PATCH v3] bpf: add inline memmove and memcpy expansion

["Jose E. Marchesi" <jose.marchesi@oracle.com>]

Hi David.

This is OK.
Thank you, very nice stuff!

> [Changes from v2: 
>  - Fix incorrectly passing a location instead of OPT_W* for warning ().
>  - Reword warning/error message and test accordingly.  ]
>  
> [Changes from v1: Jose's review comments, all of which I agree with.
>  - Fix 'implments' typo in commit message.
>  - Change check that alignment is CONST_INT to gcc_assert ().
>  - Change default case in alignment switch to gcc_unreachable ().
>  - Reword error message for non-constant size memmove/memcpy, and
>    update test for the error accordingly.
>  - Delete CPYMEM_EXPAND_ERR macro, since it was now only used in
>    one place.  ]
>
> BPF programs are not typically linked, which means we cannot fall back
> on library calls to implement __builtin_{memmove,memcpy} and should
> always expand them inline if possible.
>
> GCC already successfully expands these builtins inline in many cases,
> but failed to do so for a few for simple cases involving overlapping
> memmove in the kernel BPF selftests and was instead emitting a libcall.
>
> This patch implements a simple inline expansion of memcpy and memmove in
> the BPF backend in a verifier-friendly way, with the caveat that the
> size must be an integer constant, which is also required by clang.
>
> Tested for bpf-unknown-none on x86_64-linux-gnu host.
>
> Also tested against the BPF verifier by compiling and loading a test
> program with overlapping memmove (essentially the memmove-1.c test)
> which failed before due to a libcall, and now successfully loads and
> passes the verifier.
>
> gcc/
>
> 	* config/bpf/bpf-protos.h (bpf_expand_cpymem): New.
> 	* config/bpf/bpf.cc: (emit_move_loop, bpf_expand_cpymem): New.
> 	* config/bpf/bpf.md: (cpymemdi, movmemdi): New define_expands.
>
> gcc/testsuite/
>
> 	* gcc.target/bpf/memcpy-1.c: New test.
> 	* gcc.target/bpf/memmove-1.c: New test.
> 	* gcc.target/bpf/memmove-2.c: New test.
> ---
>  gcc/config/bpf/bpf-protos.h              |   2 +
>  gcc/config/bpf/bpf.cc                    | 115 +++++++++++++++++++++++
>  gcc/config/bpf/bpf.md                    |  36 +++++++
>  gcc/testsuite/gcc.target/bpf/memcpy-1.c  |  26 +++++
>  gcc/testsuite/gcc.target/bpf/memmove-1.c |  46 +++++++++
>  gcc/testsuite/gcc.target/bpf/memmove-2.c |  23 +++++
>  6 files changed, 248 insertions(+)
>  create mode 100644 gcc/testsuite/gcc.target/bpf/memcpy-1.c
>  create mode 100644 gcc/testsuite/gcc.target/bpf/memmove-1.c
>  create mode 100644 gcc/testsuite/gcc.target/bpf/memmove-2.c
>
> diff --git a/gcc/config/bpf/bpf-protos.h b/gcc/config/bpf/bpf-protos.h
> index 46d950bd990..366acb87ae4 100644
> --- a/gcc/config/bpf/bpf-protos.h
> +++ b/gcc/config/bpf/bpf-protos.h
> @@ -35,4 +35,6 @@ const char *bpf_add_core_reloc (rtx *operands, const char *templ);
>  class gimple_opt_pass;
>  gimple_opt_pass *make_pass_lower_bpf_core (gcc::context *ctxt);
>  
> +bool bpf_expand_cpymem (rtx *, bool);
> +
>  #endif /* ! GCC_BPF_PROTOS_H */
> diff --git a/gcc/config/bpf/bpf.cc b/gcc/config/bpf/bpf.cc
> index d6ca47eeecb..f9ac263613a 100644
> --- a/gcc/config/bpf/bpf.cc
> +++ b/gcc/config/bpf/bpf.cc
> @@ -1184,6 +1184,121 @@ bpf_use_by_pieces_infrastructure_p (unsigned HOST_WIDE_INT size,
>  #define TARGET_USE_BY_PIECES_INFRASTRUCTURE_P \
>    bpf_use_by_pieces_infrastructure_p
>  
> +/* Helper for bpf_expand_cpymem.  Emit an unrolled loop moving the bytes
> +   from SRC to DST.  */
> +
> +static void
> +emit_move_loop (rtx src, rtx dst, machine_mode mode, int offset, int inc,
> +		unsigned iters, unsigned remainder)
> +{
> +  rtx reg = gen_reg_rtx (mode);
> +
> +  /* First copy in chunks as large as alignment permits.  */
> +  for (unsigned int i = 0; i < iters; i++)
> +    {
> +      emit_move_insn (reg, adjust_address (src, mode, offset));
> +      emit_move_insn (adjust_address (dst, mode, offset), reg);
> +      offset += inc;
> +    }
> +
> +  /* Handle remaining bytes which might be smaller than the chunks
> +     used above.  */
> +  if (remainder & 4)
> +    {
> +      emit_move_insn (reg, adjust_address (src, SImode, offset));
> +      emit_move_insn (adjust_address (dst, SImode, offset), reg);
> +      offset += (inc < 0 ? -4 : 4);
> +      remainder -= 4;
> +    }
> +  if (remainder & 2)
> +    {
> +      emit_move_insn (reg, adjust_address (src, HImode, offset));
> +      emit_move_insn (adjust_address (dst, HImode, offset), reg);
> +      offset += (inc < 0 ? -2 : 2);
> +      remainder -= 2;
> +    }
> +  if (remainder & 1)
> +    {
> +      emit_move_insn (reg, adjust_address (src, QImode, offset));
> +      emit_move_insn (adjust_address (dst, QImode, offset), reg);
> +    }
> +}
> +
> +/* Expand cpymem/movmem, as from __builtin_memcpy/memmove.
> +   OPERANDS are the same as the cpymem/movmem patterns.
> +   IS_MOVE is true if this is a memmove, false for memcpy.
> +   Return true if we successfully expanded, or false if we cannot
> +   and must punt to a libcall.  */
> +
> +bool
> +bpf_expand_cpymem (rtx *operands, bool is_move)
> +{
> +  /* Size must be constant for this expansion to work.  */
> +  if (!CONST_INT_P (operands[2]))
> +    {
> +      const char *name = is_move ? "memmove" : "memcpy";
> +      if (flag_building_libgcc)
> +	warning (0, "could not inline call to %<__builtin_%s%>: "
> +		 "size must be constant", name);
> +      else
> +	error ("could not inline call to %<__builtin_%s%>: "
> +	       "size must be constant", name);
> +      return false;
> +    }
> +
> +  /* Alignment is a CONST_INT.  */
> +  gcc_assert (CONST_INT_P (operands[3]));
> +
> +  rtx dst = operands[0];
> +  rtx src = operands[1];
> +  rtx size = operands[2];
> +  unsigned HOST_WIDE_INT size_bytes = UINTVAL (size);
> +  unsigned align = UINTVAL (operands[3]);
> +  enum machine_mode mode;
> +  switch (align)
> +    {
> +    case 1: mode = QImode; break;
> +    case 2: mode = HImode; break;
> +    case 4: mode = SImode; break;
> +    case 8: mode = DImode; break;
> +    default:
> +      gcc_unreachable ();
> +    }
> +
> +  unsigned iters = size_bytes >> ceil_log2 (align);
> +  unsigned remainder = size_bytes & (align - 1);
> +
> +  int inc = GET_MODE_SIZE (mode);
> +  rtx_code_label *fwd_label, *done_label;
> +  if (is_move)
> +    {
> +      /* For memmove, be careful of overlap.  It is not a concern for memcpy.
> +	 To handle overlap, we check (at runtime) if SRC < DST, and if so do
> +	 the move "backwards" starting from SRC + SIZE.  */
> +      fwd_label = gen_label_rtx ();
> +      done_label = gen_label_rtx ();
> +
> +      rtx dst_addr = copy_to_mode_reg (Pmode, XEXP (dst, 0));
> +      rtx src_addr = copy_to_mode_reg (Pmode, XEXP (src, 0));
> +      emit_cmp_and_jump_insns (src_addr, dst_addr, GEU, NULL_RTX, Pmode,
> +			       true, fwd_label, profile_probability::even ());
> +
> +      /* Emit the "backwards" unrolled loop.  */
> +      emit_move_loop (src, dst, mode, size_bytes, -inc, iters, remainder);
> +      emit_jump_insn (gen_jump (done_label));
> +      emit_barrier ();
> +
> +      emit_label (fwd_label);
> +    }
> +
> +  emit_move_loop (src, dst, mode, 0, inc, iters, remainder);
> +
> +  if (is_move)
> +    emit_label (done_label);
> +
> +  return true;
> +}
> +
>  /* Finally, build the GCC target.  */
>  
>  struct gcc_target targetm = TARGET_INITIALIZER;
> diff --git a/gcc/config/bpf/bpf.md b/gcc/config/bpf/bpf.md
> index 50df1aaa3e2..ca677bc6b50 100644
> --- a/gcc/config/bpf/bpf.md
> +++ b/gcc/config/bpf/bpf.md
> @@ -627,4 +627,40 @@ (define_insn "ldabs<ldop>"
>    "{ldabs<ldop>\t%0|r0 = *(<pldop> *) skb[%0]}"
>    [(set_attr "type" "ld")])
>  
> +;;; memmove and memcopy
> +
> +;; 0 is dst
> +;; 1 is src
> +;; 2 is size of copy in bytes
> +;; 3 is alignment
> +
> +(define_expand "cpymemdi"
> +  [(match_operand:BLK 0 "memory_operand")
> +   (match_operand:BLK 1 "memory_operand")
> +   (match_operand:DI 2 "general_operand")
> +   (match_operand:DI 3 "immediate_operand")]
> +   ""
> +{
> +  if (bpf_expand_cpymem (operands, false))
> +    DONE;
> +  FAIL;
> +})
> +
> +;; 0 is dst
> +;; 1 is src
> +;; 2 is size of copy in bytes
> +;; 3 is alignment
> +
> +(define_expand "movmemdi"
> +  [(match_operand:BLK 0 "memory_operand")
> +   (match_operand:BLK 1 "memory_operand")
> +   (match_operand:DI 2 "general_operand")
> +   (match_operand:DI 3 "immediate_operand")]
> +   ""
> +{
> +  if (bpf_expand_cpymem (operands, true))
> +    DONE;
> +  FAIL;
> +})
> +
>  (include "atomic.md")
> diff --git a/gcc/testsuite/gcc.target/bpf/memcpy-1.c b/gcc/testsuite/gcc.target/bpf/memcpy-1.c
> new file mode 100644
> index 00000000000..6c9707f24e8
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/bpf/memcpy-1.c
> @@ -0,0 +1,26 @@
> +/* Ensure memcpy is expanded inline rather than emitting a libcall.  */
> +
> +/* { dg-do compile } */
> +/* { dg-options "-O2" } */
> +
> +struct context {
> + unsigned int data;
> + unsigned int data_end;
> + unsigned int data_meta;
> + unsigned int ingress;
> + unsigned int queue_index;
> + unsigned int egress;
> +};
> +
> +void
> +cpy_1(struct context *ctx)
> +{
> +  void *data = (void *)(long)ctx->data;
> +  char *dest;
> +  dest = data;
> +  dest += 16;
> +
> +  __builtin_memcpy (dest, data, 8);
> +}
> +
> +/* { dg-final { scan-assembler-times "call" 0 } } */
> diff --git a/gcc/testsuite/gcc.target/bpf/memmove-1.c b/gcc/testsuite/gcc.target/bpf/memmove-1.c
> new file mode 100644
> index 00000000000..3b8ba82639e
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/bpf/memmove-1.c
> @@ -0,0 +1,46 @@
> +/* Ensure memmove is expanded inline rather than emitting a libcall.  */
> +
> +/* { dg-do compile } */
> +/* { dg-options "-O2" } */
> +
> +struct context {
> + unsigned int data;
> + unsigned int data_end;
> + unsigned int data_meta;
> + unsigned int ingress;
> + unsigned int queue_index;
> + unsigned int egress;
> +};
> +
> +void
> +mov_1_nooverlap (struct context *ctx)
> +{
> +  void *data = (void *)(long)ctx->data;
> +  char *dest;
> +  dest = data;
> +  dest += 16;
> +
> +  __builtin_memmove (dest, data, 12);
> +}
> +
> +void
> +mov_1_overlap (struct context *ctx)
> +{
> +  void *data = (void *)(long)ctx->data;
> +  char *dest;
> +  dest = data;
> +  dest += 4;
> +
> +  __builtin_memmove (dest, data, 12);
> +}
> +
> +void
> +mov_1_arbitrary (struct context *ctx_a, struct context *ctx_b)
> +{
> +  void *src = (void *)(long)ctx_a->data;
> +  void *dst = (void *)(long)ctx_b->data;
> +
> +  __builtin_memmove (dst, src, 12);
> +}
> +
> +/* { dg-final { scan-assembler-times "call" 0 } } */
> diff --git a/gcc/testsuite/gcc.target/bpf/memmove-2.c b/gcc/testsuite/gcc.target/bpf/memmove-2.c
> new file mode 100644
> index 00000000000..c0f92d40d92
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/bpf/memmove-2.c
> @@ -0,0 +1,23 @@
> +/* Test that we error if memmove cannot be expanded inline.  */
> +
> +/* { dg-do compile } */
> +/* { dg-options "-O2" } */
> +
> +typedef unsigned int __u32;
> +
> +struct context {
> + unsigned int data;
> + unsigned int data_end;
> + unsigned int data_meta;
> +};
> +
> +void
> +mov_2_unsupported (struct context *ctx)
> +{
> +  void *data = (void *)(long)ctx->data;
> +  char *dest;
> +  dest = data;
> +  dest += 4;
> +
> +  __builtin_memmove (dest, data, ctx->data_meta); /* { dg-error "could not inline call" } */
> +}