ping
> ping
>
>> [Differences from V1:
>> - Prototype for call_from_call_insn moved before comment block.
>> - Reuse the `call' flag for SYMBOL_REF_LIBCALL.
>> - Fallback to check REG_CALL_DECL in non-direct calls.
>> - New test to check correct behavior for non-direct calls.]
>>
>> There are many places in GCC where alternative local sequences are
>> tried in order to determine what is the cheapest or best alternative
>> to use in the current target. When any of these sequences involve a
>> libcall, the current implementation of emit_library_call_value_1
>> introduce a side-effect consisting on emitting an external declaration
>> for the funcall (such as __divdi3) which is thus emitted even if the
>> sequence that does the libcall is not retained.
>>
>> This is problematic in targets such as BPF, because the kernel loader
>> chokes on the spurious symbol __divdi3 and makes the resulting BPF
>> object unloadable. Note that BPF objects are not linked before being
>> loaded.
>>
>> This patch changes emit_library_call_value_1 to mark the target
>> SYMBOL_REF as a libcall. Then, the emission of the external
>> declaration is done in the first loop of final.cc:shorten_branches.
>> This happens only if the corresponding sequence has been kept.
>>
>> Regtested in x86_64-linux-gnu.
>> Tested with host x86_64-linux-gnu with target bpf-unknown-none.
>>
>> gcc/ChangeLog
>>
>> * rtl.h (SYMBOL_REF_LIBCALL): Define.
>> * calls.cc (emit_library_call_value_1): Do not emit external
>> libcall declaration here.
>> * final.cc (shorten_branches): Do it here.
>>
>> gcc/testsuite/ChangeLog
>>
>> * gcc.target/bpf/divmod-libcall-1.c: New test.
>> * gcc.target/bpf/divmod-libcall-2.c: Likewise.
>> * gcc.c-torture/compile/libcall-2.c: Likewise.
>> ---
>> gcc/calls.cc | 9 +++---
>> gcc/final.cc | 30 +++++++++++++++++++
>> gcc/rtl.h | 5 ++++
>> .../gcc.c-torture/compile/libcall-2.c | 8 +++++
>> .../gcc.target/bpf/divmod-libcall-1.c | 19 ++++++++++++
>> .../gcc.target/bpf/divmod-libcall-2.c | 16 ++++++++++
>> 6 files changed, 83 insertions(+), 4 deletions(-)
>> create mode 100644 gcc/testsuite/gcc.c-torture/compile/libcall-2.c
>> create mode 100644 gcc/testsuite/gcc.target/bpf/divmod-libcall-1.c
>> create mode 100644 gcc/testsuite/gcc.target/bpf/divmod-libcall-2.c
>>
>> diff --git a/gcc/calls.cc b/gcc/calls.cc
>> index 1f3a6d5c450..219ea599b16 100644
>> --- a/gcc/calls.cc
>> +++ b/gcc/calls.cc
>> @@ -4388,9 +4388,10 @@ emit_library_call_value_1 (int retval, rtx orgfun,
>> rtx value,
>> || argvec[i].partial != 0)
>> update_stack_alignment_for_call (&argvec[i].locate);
>>
>> - /* If this machine requires an external definition for library
>> - functions, write one out. */
>> - assemble_external_libcall (fun);
>> + /* Mark the emitted target as a libcall. This will be used by final
>> + in order to emit an external symbol declaration if the libcall is
>> + ever used. */
>> + SYMBOL_REF_LIBCALL (fun) = 1;
>>
>> original_args_size = args_size;
>> args_size.constant = (aligned_upper_bound (args_size.constant
>> @@ -4735,7 +4736,7 @@ emit_library_call_value_1 (int retval, rtx orgfun, rtx
>> value,
>> valreg,
>> old_inhibit_defer_pop + 1, call_fusage, flags, args_so_far);
>>
>> - if (flag_ipa_ra)
>> + if (flag_ipa_ra || SYMBOL_REF_LIBCALL (orgfun))
>> {
>> rtx datum = orgfun;
>> gcc_assert (GET_CODE (datum) == SYMBOL_REF);
>> diff --git a/gcc/final.cc b/gcc/final.cc
>> index dd3e22547ac..2041e43fdd1 100644
>> --- a/gcc/final.cc
>> +++ b/gcc/final.cc
>> @@ -804,6 +804,8 @@ make_pass_compute_alignments (gcc::context *ctxt)
>> }
>>
>>
>> +static rtx call_from_call_insn (rtx_call_insn *insn);
>> +
>> /* Make a pass over all insns and compute their actual lengths by shortening
>> any branches of variable length if possible. */
>>
>> @@ -850,6 +852,34 @@ shorten_branches (rtx_insn *first)
>> for (insn = get_insns (), i = 1; insn; insn = NEXT_INSN (insn))
>> {
>> INSN_SHUID (insn) = i++;
>> +
>> + /* If this is a `call' instruction implementing a libcall, and
>> + this machine requires an external definition for library
>> + functions, write one out. */
>> + if (CALL_P (insn))
>> + {
>> + rtx x;
>> +
>> + if ((x = call_from_call_insn (dyn_cast <rtx_call_insn *> (insn)))
>> + && (x = XEXP (x, 0))
>> + && MEM_P (x)
>> + && (x = XEXP (x, 0))
>> + && SYMBOL_REF_P (x)
>> + && SYMBOL_REF_LIBCALL (x))
>> + {
>> + /* Direct call. */
>> + assemble_external_libcall (x);
>> + }
>> + else if ((x = find_reg_note (insn, REG_CALL_DECL, NULL_RTX))
>> + && (x = XEXP (x, 0)))
>> + {
>> + /* Indirect call with REG_CALL_DECL note. */
>> + gcc_assert (SYMBOL_REF_P (x));
>> + if (SYMBOL_REF_LIBCALL (x))
>> + assemble_external_libcall (x);
>> + }
>> + }
>> +
>> if (INSN_P (insn))
>> continue;
>>
>> diff --git a/gcc/rtl.h b/gcc/rtl.h
>> index e1c51156f90..28be708a55f 100644
>> --- a/gcc/rtl.h
>> +++ b/gcc/rtl.h
>> @@ -334,6 +334,7 @@ struct GTY((desc("0"), tag("0"),
>> 1 in a CALL_INSN logically equivalent to
>> ECF_LOOPING_CONST_OR_PURE and DECL_LOOPING_CONST_OR_PURE_P.
>> 1 in a VALUE is SP_DERIVED_VALUE_P in cselib.cc.
>> + 1 in a SYMBOL_REF if it is the target of a libcall.
>> Dumped as "/c" in RTL dumps. */
>> unsigned int call : 1;
>> /* 1 in a REG, MEM, or CONCAT if the value is set at most once, anywhere.
>> @@ -2734,6 +2735,10 @@ do {
>> \
>> #define SYMBOL_REF_USED(RTX)
>> \
>> (RTL_FLAG_CHECK1 ("SYMBOL_REF_USED", (RTX), SYMBOL_REF)->used)
>>
>> +/* 1 if RTX is a symbol_ref that represents a libcall target. */
>> +#define SYMBOL_REF_LIBCALL(RTX) \
>> + (RTL_FLAG_CHECK1 ("SYMBOL_REF_LIBCALL", (RTX), SYMBOL_REF)->call)
>> +
>> /* 1 if RTX is a symbol_ref for a weak symbol. */
>> #define SYMBOL_REF_WEAK(RTX)
>> \
>> (RTL_FLAG_CHECK1 ("SYMBOL_REF_WEAK", (RTX), SYMBOL_REF)->return_val)
>> diff --git a/gcc/testsuite/gcc.c-torture/compile/libcall-2.c
>> b/gcc/testsuite/gcc.c-torture/compile/libcall-2.c
>> new file mode 100644
>> index 00000000000..b33944c83ff
>> --- /dev/null
>> +++ b/gcc/testsuite/gcc.c-torture/compile/libcall-2.c
>> @@ -0,0 +1,8 @@
>> +/* Make sure that external refences for libcalls are generated even for
>> + indirect calls. */
>> +
>> +/* { dg-do compile } */
>> +/* { dg-options "-O2 -mcmodel=large" { target x86_64-*-* } } */
>> +/* { dg-final { scan-assembler "globl\t__divti3" } } */
>> +
>> +__int128 a, b; void foo () { a = a / b; }
>> diff --git a/gcc/testsuite/gcc.target/bpf/divmod-libcall-1.c
>> b/gcc/testsuite/gcc.target/bpf/divmod-libcall-1.c
>> new file mode 100644
>> index 00000000000..7481076602a
>> --- /dev/null
>> +++ b/gcc/testsuite/gcc.target/bpf/divmod-libcall-1.c
>> @@ -0,0 +1,19 @@
>> +/* This test makes sure that no spurious external symbol declarations are
>> + emitted for libcalls in tried but eventually not used code sequences. */
>> +
>> +/* { dg-do compile } */
>> +/* { dg-options "-O2 -mcpu=v3" } */
>> +/* { dg-final { scan-assembler-not "global\t__divdi3" } } */
>> +/* { dg-final { scan-assembler-not "global\t__moddi3" } } */
>> +
>> +int
>> +foo (unsigned int len)
>> +{
>> + return ((unsigned long)len) * 234 / 5;
>> +}
>> +
>> +int
>> +bar (unsigned int len)
>> +{
>> + return ((unsigned long)len) * 234 % 5;
>> +}
>> diff --git a/gcc/testsuite/gcc.target/bpf/divmod-libcall-2.c
>> b/gcc/testsuite/gcc.target/bpf/divmod-libcall-2.c
>> new file mode 100644
>> index 00000000000..792d689395a
>> --- /dev/null
>> +++ b/gcc/testsuite/gcc.target/bpf/divmod-libcall-2.c
>> @@ -0,0 +1,16 @@
>> +/* { dg-do compile } */
>> +/* { dg-options "-O2 -mcpu=v3" } */
>> +/* { dg-final { scan-assembler "global\t__divdi3" } } */
>> +/* { dg-final { scan-assembler "global\t__moddi3" } } */
>> +
>> +int
>> +foo (unsigned int len)
>> +{
>> + return ((long)len) * 234 / 5;
>> +}
>> +
>> +int
>> +bar (unsigned int len)
>> +{
>> + return ((long)len) * 234 % 5;
>> +}
