On Thu, May 8, 2025 at 11:11 AM H.J. Lu <hjl.to...@gmail.com> wrote:
>
> Conditional and unconditional branch targets can be either a label or
> a symbol. For conditional jump:
>
> (jump_insn 7 6 14 2 (set (pc)
> (if_then_else (eq (reg:CCZ 17 flags)
> (const_int 0 [0]))
> (label_ref:DI 23)
> (pc))) "x.c":8:5 1458 {jcc}
> (expr_list:REG_DEAD (reg:CCZ 17 flags)
> (int_list:REG_BR_PROB 217325348 (nil)))
> ...
> (code_label 23 20 8 4 4 (nil) [1 uses])
> (note 8 23 9 4 [bb 4] NOTE_INSN_BASIC_BLOCK)
> (call_insn/j 9 8 10 4 (call (mem:QI (symbol_ref:DI ("bar") [flags 0x41]
> <function_decl 0x7f4cff3c0b00 bar>) [0 bar S1 A8])
> (const_int 0 [0])) "x.c":8:14 discrim 1 1469 {sibcall_di}
> (expr_list:REG_CALL_DECL (symbol_ref:DI ("bar") [flags 0x41]
> <function_dec
> l 0x7f4cff3c0b00 bar>)
> (nil))
> (nil))
>
> they can be changed to
>
> (jump_insn 7 6 14 2 (set (pc)
> (if_then_else (eq (reg:CCZ 17 flags)
> (const_int 0 [0]))
> ((symbol_ref:DI ("bar") [flags 0x41] <function_decl
> 0x7fffe99c0c00 foo>)
> (pc))) "x.c":8:5 1458 {jcc}
> (expr_list:REG_DEAD (reg:CCZ 17 flags)
> (int_list:REG_BR_PROB 217325348 (nil)))
>
> if the call is a sibcall. For jump table:
>
> (jump_table_data 16 15 17 (addr_vec:DI [
> (label_ref:DI 18)
> (label_ref:DI 22)
> (label_ref:DI 26)
> (label_ref:DI 30)
> (label_ref:DI 34)
> ]))
> ...
> (code_label 30 17 31 4 5 (nil) [1 uses])
> (note 31 30 32 4 [bb 4] NOTE_INSN_BASIC_BLOCK)
> (call_insn/j 32 31 33 4 (call (mem:QI (symbol_ref:DI ("bar3") [flags 0x41]
> <function_decl 0x7f21be3c0e00 bar3>) [0 bar3 S1 A8])
> (const_int 0 [0])) "j.c":15:13 1469 {sibcall_di}
> (expr_list:REG_CALL_DECL (symbol_ref:DI ("bar3") [flags 0x41]
> <function_decl 0x7f21be3c0e00 bar3>)
> (nil))
> (nil))
>
> They can be changed to
>
> (jump_table_data 16 15 17 (addr_vec:DI [
> (symbol_ref:DI ("bar0") [flags 0x41] <function_decl
> 0x7f4f1c5c0b00 bar0>)
> (symbol_ref:DI ("bar1") [flags 0x41] <function_decl
> 0x7f4f1c5c0c00 bar1>)
> (symbol_ref:DI ("bar2") [flags 0x41] <function_decl
> 0x7f4f1c5c0d00 bar2>)
> (symbol_ref:DI ("bar3") [flags 0x41] <function_decl
> 0x7f4f1c5c0e00 bar3>)
> (symbol_ref:DI ("bar4") [flags 0x41] <function_decl
> 0x7f4f1c5c0f00 bar4>)
> ]))
>
> if bar0/bar1/bar2/bar3/bar4 calls are sibcalls.
>
> Instead of supporting symbol reference in jump label and jump table in
> the full RTL optimization pipeline, which requires very invasive changes
> to GCC RTL infrastructure, support symbol reference in jump label and
> jump table for the pass which turning REG_EH_REGION notes back into
> NOTE_INSN_EH_REGION notes and after:
>
> 1. Add a set_jump_target method to assign symbol reference to jump label.
> 2. Add condsibcall_p for conditional sibling call.
> 3. Add anycall_p to return true for call and conditional sibcall.
> 4. Replace CALL_P with anycall_p in except.cc, final.cc and function-abi.cc
> to support conditional sibcall.
> 5. Return false for symbol reference in jump table check.
> 6. Update create_trace_edges and rtx_writer::print_rtx_operand_code_0 to
> handle symbol reference in jump label.
> 7. Update to final_scan_insn_1 to handle symbol reference in jump table.
> 8. Document limitation of symbol reference support in jump label.
>
> * dwarf2cfi.c (create_trace_edges): Skip symbol reference in
> jump table and in JUMP_LABEL. Short-circuit JUMP for the pure
> sibcall.
> * except.cc (sjlj_mark_call_sites): Replace CALL_P with
> anycall_p.
> (finish_eh_generation): Likewise.
> (insn_could_throw_p): Likewise.
> (can_nonlocal_goto): Likewise.
> (set_nothrow_function_flags): Also call condsibcall_p to check
> conditional sibcall.
> * final.cc (final_scan_insn_1): Support symbol reference in jump
> table.
> (collect_fn_hard_reg_usage): Replace CALL_P with anycall_p.
> * function-abi.cc (insn_callee_abi): Likewise.
> * jump.cc (condsibcall_p): New.
> * print-rtl.cc (rtx_writer::print_rtx_operand_code_0): Support
> symbol reference in JUMP_LABEL.
> * rtl.h (rtx_jump_insn::set_jump_target): New, with the rtx
> argument.
> * rtl.h (condsibcall_p): New.
> (anycall_p): Likewise.
> * rtlanal.cc (tablejump_p): Return false if JUMP_LABEL is a
> symbol reference.
> * config/i386/i386-expand.cc (ix86_notrack_prefixed_insn_p):
> Likewise.
> * doc/rtl.texi (addr_vec): Also allow symbol reference.
> (JUMP_LABEL): Likewise.
>
> Signed-off-by: H.J. Lu <hjl.to...@gmail.com>
> ---
> gcc/config/i386/i386-expand.cc | 5 ++++-
> gcc/doc/rtl.texi | 24 +++++++++++++----------
> gcc/dwarf2cfi.cc | 20 ++++++++++++++++++-
> gcc/except.cc | 11 ++++++-----
> gcc/final.cc | 26 +++++++++++++++++++++---
> gcc/function-abi.cc | 2 +-
> gcc/jump.cc | 36 ++++++++++++++++++++++++++++++++++
> gcc/print-rtl.cc | 2 ++
> gcc/rtl.h | 32 ++++++++++++++++++++++++++++++
> gcc/rtlanal.cc | 5 ++++-
> 10 files changed, 141 insertions(+), 22 deletions(-)
>
> diff --git a/gcc/config/i386/i386-expand.cc b/gcc/config/i386/i386-expand.cc
> index 7f0fdb6fa9e..0d0802692d1 100644
> --- a/gcc/config/i386/i386-expand.cc
> +++ b/gcc/config/i386/i386-expand.cc
> @@ -25501,7 +25501,10 @@ ix86_notrack_prefixed_insn_p (rtx_insn *insn)
> if (JUMP_P (insn) && !flag_cet_switch)
> {
> rtx target = JUMP_LABEL (insn);
> - if (target == NULL_RTX || ANY_RETURN_P (target))
> + if (target == NULL_RTX
> + || ANY_RETURN_P (target)
> + /* Also check for conditional sibcall. */
> + || SYMBOL_REF_P (target))
> return false;
>
> /* Check the jump is a switch table. */
> diff --git a/gcc/doc/rtl.texi b/gcc/doc/rtl.texi
> index 089bb1c4ede..0976c9c82dd 100644
> --- a/gcc/doc/rtl.texi
> +++ b/gcc/doc/rtl.texi
> @@ -3459,8 +3459,9 @@ insn, inside a @code{parallel}, or inside an expression.
> @findex addr_vec
> @item (addr_vec:@var{m} [@var{lr0} @var{lr1} @dots{}])
> Represents a table of jump addresses. The vector elements @var{lr0},
> -etc., are @code{label_ref} expressions. The mode @var{m} specifies
> -how much space is given to each address; normally @var{m} would be
> +etc., are @code{label_ref} or @code{symbol_ref} expressions. The mode
> +@var{m} specifies how much space is given to each address; normally
> +@var{m} would be
> @code{Pmode}.
>
> @findex addr_diff_vec
> @@ -3780,14 +3781,17 @@ instruction to return from the current function, it
> is recorded as a
> accessed in the same way and in addition contain a field
> @code{JUMP_LABEL} which is defined once jump optimization has completed.
>
> -For simple conditional and unconditional jumps, this field contains
> -the @code{code_label} to which this insn will (possibly conditionally)
> -branch. In a more complex jump, @code{JUMP_LABEL} records one of the
> -labels that the insn refers to; other jump target labels are recorded
> -as @code{REG_LABEL_TARGET} notes. The exception is @code{addr_vec}
> -and @code{addr_diff_vec}, where @code{JUMP_LABEL} is @code{NULL_RTX}
> -and the only way to find the labels is to scan the entire body of the
> -insn.
> +For unconditional jumps, this field contains the @code{code_label} to
> +which this insn will branch. For simple conditional jumps, this field
> +contains the @code{code_label} or @code{symbol_ref} to which this insn
> +will branch possibly conditionally. @code{symbol_ref} should only be
> +generated immediately before the pass which turning REG_EH_REGION notes
> +back into NOTE_INSN_EH_REGION notes. In a more complex jump,
> +@code{JUMP_LABEL} records one of the labels that the insn refers to;
> +other jump target labels are recorded as @code{REG_LABEL_TARGET} notes.
> +The exception is @code{addr_vec} and @code{addr_diff_vec}, where
> +@code{JUMP_LABEL} is @code{NULL_RTX} and the only way to find the labels
> +is to scan the entire body of the insn.
>
> Return insns count as jumps, but their @code{JUMP_LABEL} is @code{RETURN}
> or @code{SIMPLE_RETURN}.
> diff --git a/gcc/dwarf2cfi.cc b/gcc/dwarf2cfi.cc
> index a5353d39e7e..d8f25123284 100644
> --- a/gcc/dwarf2cfi.cc
> +++ b/gcc/dwarf2cfi.cc
> @@ -2646,6 +2646,8 @@ create_trace_edges (rtx_insn *insn)
> if (JUMP_P (insn))
> {
> rtx_jump_table_data *table;
> + bool sibcall_p = false;
> + bool label_p = false;
>
> if (find_reg_note (insn, REG_NON_LOCAL_GOTO, NULL_RTX))
> return;
> @@ -2657,8 +2659,17 @@ create_trace_edges (rtx_insn *insn)
> n = GET_NUM_ELEM (vec);
> for (i = 0; i < n; ++i)
> {
> - rtx_insn *lab = as_a <rtx_insn *> (XEXP (RTVEC_ELT (vec, i),
> 0));
> + rtx l = RTVEC_ELT (vec, i);
> + if (SYMBOL_REF_P (l))
> + {
> + /* A symbol reference must be a sibcall. Skip it. */
> + sibcall_p = true;
> + continue;
> + }
> + l = XEXP (l, 0);
> + rtx_insn *lab = as_a <rtx_insn *> (l);
> maybe_record_trace_start (lab, insn);
> + label_p = true;
> }
>
> /* Handle casesi dispatch insns. */
> @@ -2687,12 +2698,19 @@ create_trace_edges (rtx_insn *insn)
> maybe_record_trace_start (lab, insn);
> }
> }
> + /* A symbol reference must be a sibcall. */
> + else if (SYMBOL_REF_P (JUMP_LABEL (insn)))
> + sibcall_p = true;
> else
> {
> rtx_insn *lab = JUMP_LABEL_AS_INSN (insn);
> gcc_assert (lab != NULL);
> maybe_record_trace_start (lab, insn);
> }
> +
> + /* Check for the pure sibcall. */
> + if (sibcall_p && !label_p)
> + return;
> }
> else if (CALL_P (insn))
> {
> diff --git a/gcc/except.cc b/gcc/except.cc
> index 0fe1e093489..2f37e4652b9 100644
> --- a/gcc/except.cc
> +++ b/gcc/except.cc
> @@ -1154,7 +1154,7 @@ sjlj_mark_call_sites (void)
>
> /* Don't separate a call from it's argument loads. */
> before = insn;
> - if (CALL_P (insn))
> + if (anycall_p (insn))
> before = find_first_parameter_load (insn, NULL);
>
> start_sequence ();
> @@ -1567,7 +1567,7 @@ finish_eh_generation (void)
> gcc_assert (BB_HEAD (e->dest) == label_rtx (lp->post_landing_pad));
>
> redirect_edge_succ (e, BLOCK_FOR_INSN (lp->landing_pad));
> - e->flags |= (CALL_P (BB_END (bb))
> + e->flags |= (anycall_p (BB_END (bb))
> ? EDGE_ABNORMAL | EDGE_ABNORMAL_CALL
> : EDGE_ABNORMAL);
> }
> @@ -1763,7 +1763,7 @@ insn_could_throw_p (const_rtx insn)
> {
> if (!flag_exceptions)
> return false;
> - if (CALL_P (insn))
> + if (anycall_p (insn))
> return true;
> if (INSN_P (insn) && cfun->can_throw_non_call_exceptions)
> return may_trap_p (PATTERN (insn));
> @@ -1980,7 +1980,7 @@ insn_nothrow_p (const_rtx insn)
> bool
> can_nonlocal_goto (const rtx_insn *insn)
> {
> - if (nonlocal_goto_handler_labels && CALL_P (insn))
> + if (nonlocal_goto_handler_labels && anycall_p (insn))
> {
> rtx note = find_reg_note (insn, REG_EH_REGION, NULL_RTX);
> if (!note || INTVAL (XEXP (note, 0)) != INT_MIN)
> @@ -2020,7 +2020,8 @@ set_nothrow_function_flags (void)
> {
> crtl->nothrow = 0;
>
> - if (!CALL_P (insn) || !SIBLING_CALL_P (insn))
> + if ((!CALL_P (insn) || !SIBLING_CALL_P (insn))
> + && !condsibcall_p (insn))
> {
> crtl->all_throwers_are_sibcalls = 0;
> return 0;
> diff --git a/gcc/final.cc b/gcc/final.cc
> index 12c6eb0ac09..bff6bf3fd86 100644
> --- a/gcc/final.cc
> +++ b/gcc/final.cc
> @@ -2524,13 +2524,33 @@ final_scan_insn_1 (rtx_insn *insn, FILE *file, int
> optimize_p ATTRIBUTE_UNUSED,
> }
> #else
> vlen = XVECLEN (body, GET_CODE (body) == ADDR_DIFF_VEC);
> +#ifdef ASM_OUTPUT_ADDR_VEC_ELT
> + const char *asm_op = integer_asm_op (POINTER_SIZE_UNITS, true);
> +#endif
> for (idx = 0; idx < vlen; idx++)
> {
> if (GET_CODE (body) == ADDR_VEC)
> {
> #ifdef ASM_OUTPUT_ADDR_VEC_ELT
> - ASM_OUTPUT_ADDR_VEC_ELT
> - (file, CODE_LABEL_NUMBER (XEXP (XVECEXP (body, 0, idx),
> 0)));
> + rtx l = XVECEXP (body, 0, idx);
> + if (SYMBOL_REF_P (l))
> + {
> + gcc_assert (asm_op != NULL);
> + fprintf (file, "%s", asm_op);
> + assemble_external (SYMBOL_REF_DECL (l));
> +#ifdef ASM_OUTPUT_SYMBOL_REF
> + ASM_OUTPUT_SYMBOL_REF (file, l);
> +#else
> + assemble_name (file, XSTR (l, 0));
> +#endif
> + putc ('\n', file);
> + }
> + else
> + {
> + l = XEXP (l, 0);
> + ASM_OUTPUT_ADDR_VEC_ELT
> + (file, CODE_LABEL_NUMBER (l));
> + }
> #else
> gcc_unreachable ();
> #endif
> @@ -4604,7 +4624,7 @@ collect_fn_hard_reg_usage (void)
> if (!NONDEBUG_INSN_P (insn))
> continue;
>
> - if (CALL_P (insn)
> + if (anycall_p (insn)
> && !self_recursive_call_p (insn))
> function_used_regs
> |= insn_callee_abi (insn).full_and_partial_reg_clobbers ();
> diff --git a/gcc/function-abi.cc b/gcc/function-abi.cc
> index d500657b49e..3cabe67af73 100644
> --- a/gcc/function-abi.cc
> +++ b/gcc/function-abi.cc
> @@ -218,7 +218,7 @@ fndecl_abi (const_tree fndecl)
> function_abi
> insn_callee_abi (const rtx_insn *insn)
> {
> - gcc_assert (insn && CALL_P (insn));
> + gcc_assert (insn && anycall_p (insn));
>
> if (flag_ipa_ra)
> if (tree fndecl = get_call_fndecl (insn))
> diff --git a/gcc/jump.cc b/gcc/jump.cc
> index 02df75ab08e..b7768a8b53f 100644
> --- a/gcc/jump.cc
> +++ b/gcc/jump.cc
> @@ -1011,6 +1011,42 @@ jump_to_label_p (const rtx_insn *insn)
> return (JUMP_P (insn)
> && JUMP_LABEL (insn) != NULL && !ANY_RETURN_P (JUMP_LABEL (insn)));
> }
> +
> +/* Return true if INSN has a conditional sibling call. */
> +
> +bool
> +condsibcall_p (const rtx_insn *insn)
> +{
> + if (!JUMP_P (insn))
> + return false;
> +
> + rtx label = JUMP_LABEL (insn);
> + if (label == nullptr || ANY_RETURN_P (label))
> + return false;
> +
> + /* Check the direct conditional sibling call. */
> + if (SYMBOL_REF_P (label))
> + return true;
> +
> + /* Check jump table with the indirect conditional sibling call. */
> + rtx_insn *target = as_a<rtx_insn *> (label);
> + rtx_insn *table = next_insn (target);
> + if (!table
> + || !JUMP_TABLE_DATA_P (table)
> + || GET_CODE (PATTERN (table)) != ADDR_VEC)
> + return false;
> +
> + rtx body = PATTERN (table);
> + unsigned int len = XVECLEN (body, 0);
> + for (unsigned int i = 0; i < len; i++)
> + {
> + rtx target = XVECEXP (body, 0, i);
> + if (SYMBOL_REF_P (target))
> + return true;
> + }
> +
> + return false;
> +}
>
> /* Find all CODE_LABELs referred to in X, and increment their use
> counts. If INSN is a JUMP_INSN and there is at least one
> diff --git a/gcc/print-rtl.cc b/gcc/print-rtl.cc
> index 033f7e7aab0..3ed7130ee1c 100644
> --- a/gcc/print-rtl.cc
> +++ b/gcc/print-rtl.cc
> @@ -308,6 +308,8 @@ rtx_writer::print_rtx_operand_code_0 (const_rtx in_rtx
> ATTRIBUTE_UNUSED,
> fprintf (m_outfile, "return");
> else if (GET_CODE (JUMP_LABEL (in_rtx)) == SIMPLE_RETURN)
> fprintf (m_outfile, "simple_return");
> + else if (SYMBOL_REF_P (JUMP_LABEL (in_rtx)))
> + print_rtx_operand_code_0 (JUMP_LABEL (in_rtx), idx);
> else
> fprintf (m_outfile, "%d", INSN_UID (JUMP_LABEL (in_rtx)));
> }
> diff --git a/gcc/rtl.h b/gcc/rtl.h
> index cc25aed1f49..0d665b74c7a 100644
> --- a/gcc/rtl.h
> +++ b/gcc/rtl.h
> @@ -625,6 +625,7 @@ public:
> /* Set jump target. */
>
> inline void set_jump_target (rtx_code_label *);
> + inline void set_jump_target (rtx);
> };
>
> struct GTY(()) rtx_call_insn : public rtx_insn
> @@ -1895,6 +1896,12 @@ inline void rtx_jump_insn::set_jump_target
> (rtx_code_label *target)
> JUMP_LABEL (this) = target;
> }
>
> +inline void rtx_jump_insn::set_jump_target (rtx target)
> +{
> + gcc_assert (SYMBOL_REF_P (target) || LABEL_P (target));
> + JUMP_LABEL (this) = target;
> +}
> +
> /* Once basic blocks are found, each CODE_LABEL starts a chain that
> goes through all the LABEL_REFs that jump to that label. The chain
> eventually winds up at the CODE_LABEL: it is circular. */
> @@ -4175,6 +4182,7 @@ extern bool jump_to_label_p (const rtx_insn *);
> extern bool condjump_p (const rtx_insn *);
> extern bool any_condjump_p (const rtx_insn *);
> extern bool any_uncondjump_p (const rtx_insn *);
> +extern bool condsibcall_p (const rtx_insn *);
> extern rtx pc_set (const rtx_insn *);
> extern rtx condjump_label (const rtx_insn *);
> extern bool simplejump_p (const rtx_insn *);
> @@ -4635,6 +4643,30 @@ word_register_operation_p (const_rtx x)
> }
> }
>
> +/* Return true if INSN is a conditional sibcall. */
> +
> +inline bool
> +condsibcall_p (const_rtx insn)
> +{
> + return condsibcall_p (as_a <const rtx_insn *> (insn));
> +}
> +
> +/* Return true if INSN is a call or a conditional sibcall. */
> +
> +inline bool
> +anycall_p (const rtx_insn *insn)
> +{
> + return CALL_P (insn) || condsibcall_p (insn);
> +}
> +
> +/* Return true if INSN is a call or a conditional sibcall. */
> +
> +inline bool
> +anycall_p (const_rtx insn)
> +{
> + return CALL_P (insn) || condsibcall_p (insn);
> +}
> +
> /* Holds an rtx comparison to simplify passing many parameters pertaining to
> a
> single comparison. */
>
> diff --git a/gcc/rtlanal.cc b/gcc/rtlanal.cc
> index 86a5e473308..915a5d4634d 100644
> --- a/gcc/rtlanal.cc
> +++ b/gcc/rtlanal.cc
> @@ -3539,7 +3539,10 @@ tablejump_p (const rtx_insn *insn, rtx_insn **labelp,
> return false;
>
> rtx target = JUMP_LABEL (insn);
> - if (target == NULL_RTX || ANY_RETURN_P (target))
> + if (target == NULL_RTX
> + || ANY_RETURN_P (target)
> + /* Also check for conditional sibcall. */
> + || SYMBOL_REF_P (target))
> return false;
>
> rtx_insn *label = as_a<rtx_insn *> (target);
> --
> 2.49.0
>
--
H.J.
