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 } } */