Hi Faust.
OK. Thanks!
> [Changes from v1:
> - Error if threshold is exceeded instead of silently emitting libcall
> - Update test accordingly
> - Expand documentation to explain this behavior ]
>
> BPF cannot fall back on library calls to implement memmove, memcpy and
> memset, so we attempt to expand these inline always if possible.
> However, this inline expansion was being attempted even for excessively
> large operations, which could result in gcc consuming huge amounts of
> memory and hanging.
>
> Add a size threshold in the BPF backend below which to always expand
> these operations inline, and introduce an option
> -minline-memops-threshold= to control the threshold. Defaults to
> 1024 bytes.
>
> gcc/
>
> * config/bpf/bpf.cc (bpf_expand_cpymem, bpf_expand_setmem): Do
> not attempt inline expansion if size is above threshold.
> * config/bpf/bpf.opt (-minline-memops-threshold): New option.
> * doc/invoke.texi (eBPF Options) <-minline-memops-threshold>:
> Document.
>
> gcc/testsuite/
>
> * gcc.target/bpf/inline-memops-threshold-1.c: New test.
> * gcc.target/bpf/inline-memops-threshold-2.c: New test.
> ---
> gcc/config/bpf/bpf.cc | 26 ++++++++++++++++++-
> gcc/config/bpf/bpf.opt | 4 +++
> gcc/doc/invoke.texi | 11 +++++++-
> .../bpf/inline-memops-threshold-1.c | 15 +++++++++++
> .../bpf/inline-memops-threshold-2.c | 11 ++++++++
> 5 files changed, 65 insertions(+), 2 deletions(-)
> create mode 100644 gcc/testsuite/gcc.target/bpf/inline-memops-threshold-1.c
> create mode 100644 gcc/testsuite/gcc.target/bpf/inline-memops-threshold-2.c
>
> diff --git a/gcc/config/bpf/bpf.cc b/gcc/config/bpf/bpf.cc
> index 0e33f4347ba..8365cd9fcb1 100644
> --- a/gcc/config/bpf/bpf.cc
> +++ b/gcc/config/bpf/bpf.cc
> @@ -1244,9 +1244,9 @@ bool
> bpf_expand_cpymem (rtx *operands, bool is_move)
> {
> /* Size must be constant for this expansion to work. */
> + const char *name = is_move ? "memmove" : "memcpy";
> 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);
> @@ -1275,6 +1275,18 @@ bpf_expand_cpymem (rtx *operands, bool is_move)
> gcc_unreachable ();
> }
>
> + /* For sizes above threshold, always use a libcall. */
> + if (size_bytes > (unsigned HOST_WIDE_INT) bpf_inline_memops_threshold)
> + {
> + if (flag_building_libgcc)
> + warning (0, "could not inline call to %<__builtin_%s%>: "
> + "too many bytes, use -minline-memops-threshold", name);
> + else
> + error ("could not inline call to %<__builtin_%s%>: "
> + "too many bytes, use -minline-memops-threshold", name);
> + return false;
> + }
> +
> unsigned iters = size_bytes >> ceil_log2 (align);
> unsigned remainder = size_bytes & (align - 1);
>
> @@ -1347,6 +1359,18 @@ bpf_expand_setmem (rtx *operands)
> gcc_unreachable ();
> }
>
> + /* For sizes above threshold, always use a libcall. */
> + if (size_bytes > (unsigned HOST_WIDE_INT) bpf_inline_memops_threshold)
> + {
> + if (flag_building_libgcc)
> + warning (0, "could not inline call to %<__builtin_memset%>: "
> + "too many bytes, use -minline-memops-threshold");
> + else
> + error ("could not inline call to %<__builtin_memset%>: "
> + "too many bytes, use -minline-memops-threshold");
> + return false;
> + }
> +
> unsigned iters = size_bytes >> ceil_log2 (align);
> unsigned remainder = size_bytes & (align - 1);
> unsigned inc = GET_MODE_SIZE (mode);
> diff --git a/gcc/config/bpf/bpf.opt b/gcc/config/bpf/bpf.opt
> index acfddebdad7..541ebe4dfc4 100644
> --- a/gcc/config/bpf/bpf.opt
> +++ b/gcc/config/bpf/bpf.opt
> @@ -108,3 +108,7 @@ Enum(asm_dialect) String(normal) Value(ASM_NORMAL)
>
> EnumValue
> Enum(asm_dialect) String(pseudoc) Value(ASM_PSEUDOC)
> +
> +minline-memops-threshold=
> +Target RejectNegative Joined UInteger Var(bpf_inline_memops_threshold)
> Init(1024)
> +-minline-memops-threshold=<number> Maximum size of memset/memmove/memcpy to
> inline, larger sizes will use a library call.
> diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
> index c0d604a2c5c..85c938d4a14 100644
> --- a/gcc/doc/invoke.texi
> +++ b/gcc/doc/invoke.texi
> @@ -971,7 +971,7 @@ Objective-C and Objective-C++ Dialects}.
> @gccoptlist{-mbig-endian -mlittle-endian
> -mframe-limit=@var{bytes} -mxbpf -mco-re -mno-co-re -mjmpext
> -mjmp32 -malu32 -mv3-atomics -mbswap -msdiv -msmov -mcpu=@var{version}
> --masm=@var{dialect}}
> +-masm=@var{dialect} -minline-memops-threshold=@var{bytes}}
>
> @emph{FR30 Options}
> @gccoptlist{-msmall-model -mno-lsim}
> @@ -25701,6 +25701,15 @@ Outputs pseudo-c assembly dialect.
>
> @end table
>
> +@opindex -minline-memops-threshold
> +@item -minline-memops-threshold=@var{bytes}
> +Specifies a size threshold in bytes at or below which memmove, memcpy
> +and memset shall always be expanded inline. Operations dealing with
> +sizes larger than this threshold would have to be be implemented using
> +a library call instead of being expanded inline, but since BPF doesn't
> +allow libcalls, exceeding this threshold results in a compile-time
> +error. The default is @samp{1024} bytes.
> +
> @end table
>
> @node FR30 Options
> diff --git a/gcc/testsuite/gcc.target/bpf/inline-memops-threshold-1.c
> b/gcc/testsuite/gcc.target/bpf/inline-memops-threshold-1.c
> new file mode 100644
> index 00000000000..c2ba4db5b7b
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/bpf/inline-memops-threshold-1.c
> @@ -0,0 +1,15 @@
> +
> +/* { dg-do compile } */
> +/* { dg-options "-O2" "-minline-memops-threshold=256"} */
> +
> +char buf[512];
> +
> +void
> +mov_small (void)
> +{
> + __builtin_memmove (buf, buf + 2, 255);
> +}
> +
> +/* { dg-final { scan-assembler-not "call" } } */
> +/* { dg-final { scan-assembler "ldxb" } } */
> +/* { dg-final { scan-assembler "stxb" } } */
> diff --git a/gcc/testsuite/gcc.target/bpf/inline-memops-threshold-2.c
> b/gcc/testsuite/gcc.target/bpf/inline-memops-threshold-2.c
> new file mode 100644
> index 00000000000..50910483890
> --- /dev/null
> +++ b/gcc/testsuite/gcc.target/bpf/inline-memops-threshold-2.c
> @@ -0,0 +1,11 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -minline-memops-threshold=256" } */
> +
> +char buf[512];
> +
> +void
> +mov_big (void)
> +{
> + __builtin_memmove (buf, buf + 12, 354); /* { dg-error "too many bytes" } */
> +}
> +
