Hi David.
Thanks for the patch.
OK.
> Similar to memmove and memcpy, the BPF backend cannot fall back on a
> library call to implement __builtin_memset, and should always expand
> calls to it inline if possible.
>
> This patch implements simple inline expansion of memset in the BPF
> backend in a verifier-friendly way. Similar to memcpy and memmove, the
> size must be an integer constant, as is also required by clang.
>
> Tested for bpf-unknown-none target on x86_64-linux-gnu host.
> Also testetd against kernel BPF verifier by compiling and loading a
> test program using the inline memset expansion.
>
> gcc/
> * config/bpf/bpf-protos.h (bpf_expand_setmem): New prototype.
> * config/bpf/bpf.cc (bpf_expand_setmem): New.
> * config/bpf/bpf.md (setmemdi): New define_expand.
>
> gcc/testsuite/
> * gcc.target/bpf/memset-1.c: New test.
> ---
> gcc/config/bpf/bpf-protos.h | 1 +
> gcc/config/bpf/bpf.cc | 66 +++++++++++++++++++++++++
> gcc/config/bpf/bpf.md | 17 +++++++
> gcc/testsuite/gcc.target/bpf/memset-1.c | 39 +++++++++++++++
> 4 files changed, 123 insertions(+)
> create mode 100644 gcc/testsuite/gcc.target/bpf/memset-1.c
>
> diff --git a/gcc/config/bpf/bpf-protos.h b/gcc/config/bpf/bpf-protos.h
> index 366acb87ae4..ac0c2f4038f 100644
> --- a/gcc/config/bpf/bpf-protos.h
> +++ b/gcc/config/bpf/bpf-protos.h
> @@ -36,5 +36,6 @@ class gimple_opt_pass;
> gimple_opt_pass *make_pass_lower_bpf_core (gcc::context *ctxt);
>
> bool bpf_expand_cpymem (rtx *, bool);
> +bool bpf_expand_setmem (rtx *);
>
> #endif /* ! GCC_BPF_PROTOS_H */
> diff --git a/gcc/config/bpf/bpf.cc b/gcc/config/bpf/bpf.cc
> index 22b0cf2dc46..0e33f4347ba 100644
> --- a/gcc/config/bpf/bpf.cc
> +++ b/gcc/config/bpf/bpf.cc
> @@ -1309,6 +1309,72 @@ bpf_expand_cpymem (rtx *operands, bool is_move)
> return true;
> }
>
> +/* Expand setmem, as from __builtin_memset.
> + OPERANDS are the same as the setmem pattern.
> + Return true if the expansion was successful, false otherwise. */
> +
> +bool
> +bpf_expand_setmem (rtx *operands)
> +{
> + /* Size must be constant for this expansion to work. */
> + if (!CONST_INT_P (operands[1]))
> + {
> + if (flag_building_libgcc)
> + warning (0, "could not inline call to %<__builtin_memset%>: "
> + "size must be constant");
> + else
> + error ("could not inline call to %<__builtin_memset%>: "
> + "size must be constant");
> + return false;
> + }
> +
> + /* Alignment is a CONST_INT. */
> + gcc_assert (CONST_INT_P (operands[3]));
> +
> + rtx dst = operands[0];
> + rtx size = operands[1];
> + rtx val = 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);
> + unsigned inc = GET_MODE_SIZE (mode);
> + unsigned offset = 0;
> +
> + for (unsigned int i = 0; i < iters; i++)
> + {
> + emit_move_insn (adjust_address (dst, mode, offset), val);
> + offset += inc;
> + }
> + if (remainder & 4)
> + {
> + emit_move_insn (adjust_address (dst, SImode, offset), val);
> + offset += 4;
> + remainder -= 4;
> + }
> + if (remainder & 2)
> + {
> + emit_move_insn (adjust_address (dst, HImode, offset), val);
> + offset += 2;
> + remainder -= 2;
> + }
> + if (remainder & 1)
> + emit_move_insn (adjust_address (dst, QImode, offset), val);
> +
> + 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 ca677bc6b50..ea688aadf91 100644
> --- a/gcc/config/bpf/bpf.md
> +++ b/gcc/config/bpf/bpf.md
> @@ -663,4 +663,21 @@ (define_expand "movmemdi"
> FAIL;
> })
>
> +;; memset
> +;; 0 is dst
> +;; 1 is length
> +;; 2 is value
> +;; 3 is alignment
> +(define_expand "setmemdi"
> + [(set (match_operand:BLK 0 "memory_operand")
> + (match_operand:QI 2 "nonmemory_operand"))
> + (use (match_operand:DI 1 "general_operand"))
> + (match_operand 3 "immediate_operand")]
> + ""
> + {
> + if (bpf_expand_setmem (operands))
> + DONE;
> + FAIL;
> +})
> +
> (include "atomic.md")
> diff --git a/gcc/testsuite/gcc.target/bpf/memset-1.c
> b/gcc/testsuite/gcc.target/bpf/memset-1.c
> new file mode 100644
> index 00000000000..9e9f8eff028
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/bpf/memset-1.c
> @@ -0,0 +1,39 @@
> +/* Ensure memset 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
> +set_small (struct context *ctx)
> +{
> + void *data = (void *)(long)ctx->data;
> + char *dest = data;
> + __builtin_memset (dest + 4, 0, sizeof (struct context) - 4);
> +}
> +
> +void
> +set_large (struct context *ctx)
> +{
> + void *data = (void *)(long)ctx->data;
> + char *dest = data;
> + __builtin_memset (dest, 0xfe, 130);
> +}
> +
> +void
> +set_variable (struct context *ctx)
> +{
> + void *data = (void *)(long)ctx->data;
> + char *dest = data;
> + __builtin_memset (dest, 0xbc, ctx->data_meta); /* { dg-error "could not
> inline call" } */
> +}
> +
> +/* { dg-final { scan-assembler-times "call" 0 } } */
