On Mon, Aug 4, 2025 at 11:33 PM H.J. Lu <hjl.to...@gmail.com> wrote:
>
> On Mon, Aug 04, 2025 at 02:57:39PM +0800, Hongtao Liu wrote:
> > > > > > + rtx_insn *before = nullptr;
> > > > > > + rtx_insn *after = nullptr;
> > > > > > + if (insn == BB_HEAD (bb))
> > > > > > + before = insn;
> > > > > > + else
> > > > > > + after = insn ? PREV_INSN (insn) : BB_END (bb);
> > > > > > +
> > > > > > + /* TLS_GD and TLS_LD_BASE instructions are normal functions which
> > > > > > + clobber caller-saved registers. TLSDESC instructions are
> > > > > > special
> > > > > > + functions which only clobber RAX. If any registers clobbered
> > > > > > by
> > > > > > + the TLS instruction are live in this basic block, we must
> > > > > > insert
> > > > > > + the TLS instruction after all live registers clobbered by the
> > > > > > TLS
> > > > > > + instruction are dead. */
> > > > > > +
> > > > > > + auto_bitmap live_caller_saved_regs;
> > > > > > + bitmap in = df_live ? DF_LIVE_IN (bb) : DF_LR_IN (bb);
> > > > > > +
> > > > > > + bool flags_live_p = bitmap_bit_p (in, FLAGS_REG);
> > > > > > +
> > > > > > + unsigned int i;
> > > > > > +
> > > > > > + /* Get all live caller-saved registers. */
> > > > > > + if (kind == X86_CSE_TLSDESC)
> > > > > > + {
> > > > > > + if (bitmap_bit_p (in, AX_REG))
> > > > > > + bitmap_set_bit (live_caller_saved_regs, AX_REG);
> > > > >
> > > > > And we don't need to check for those hard registers here and below?
> > > >
> > > > TLS_GD and TLS_LD_BASE instructions are normal functions which
> > > > clobber caller-saved registers. TLSDESC instructions are special
> > > > functions which only clobber RAX. live_caller_saved_regs captures
> > > > live caller-saved registers for these TLS instructions.
> >
> > I notice those insns are CALL_INSN, and for ABI, rax/rdi/rsi is
> > caller_saved registers, so even we explicitly use (clobber (reg: RAX))
>
> Since a single TLS call will clobber caller-saved registers, it must
> be placed where all caller-saved registers are dead. Otherwise, the
> TLS call will clobber some live registers.
I saw in legitimize_tls_address, it doesn't check the liveness of
RAX/RDI(or call clobber registers) even with explicit use of RDI/RAX.
I'm wondering if we can reuse that code to do similar things.
617 if (TARGET_GNU2_TLS)
12618 {
12619 rtx tmp = ix86_tls_module_base ();
12620
12621 base = gen_reg_rtx (ptr_mode);
12622 if (TARGET_64BIT)
12623 emit_insn (gen_tls_dynamic_gnu2_64 (ptr_mode, base,
tmp));
12624 else
12625 emit_insn (gen_tls_dynamic_gnu2_32 (base, tmp, pic));
12626
12627 tp = get_thread_pointer (ptr_mode, true);
and
12632 else
12633 {
12634 rtx caddr = ix86_tls_get_addr ();
12635
12636 base = gen_reg_rtx (Pmode);
12637 if (TARGET_64BIT)
12638 {
12639 rtx rax = gen_rtx_REG (Pmode, AX_REG);
12640 rtx rdi = gen_rtx_REG (Pmode, DI_REG);
12641 rtx_insn *insns;
12642 rtx eqv;
12643
12644 start_sequence ();
12645 emit_call_insn
12646 (gen_tls_local_dynamic_base_64 (Pmode, rax,
caddr, rdi));
12647 insns = end_sequence ();
12648
12649 /* Attach a unique REG_EQUAL, to allow the RTL
optimizers to
12650 share the LD_BASE result with other LD model
accesses. */
12651 eqv = gen_rtx_UNSPEC (Pmode, gen_rtvec (1,
const0_rtx),
12652 UNSPEC_TLS_LD_BASE);
12653
12654 RTL_CONST_CALL_P (insns) = 1;
12655 emit_libcall_block (insns, base, rax, eqv);
12656 }
12657 else
12658 emit_insn (gen_tls_local_dynamic_base_32 (base, pic,
caddr));
12659 }
>
> > RA will help save and restore the register?
>
> This is unrelated to RA.
>
> > > >
> > > > rtx tls_symbol = XVECEXP (src, 0, 0);
> > > > src = XVECEXP (src, 0, 1);
> > > > ...
> > > > rtx tls_set = PATTERN (set_insn);
> > > > rtx tls_src = XVECEXP (SET_SRC (tls_set), 0, 0);
> > > > if (!rtx_equal_p (tls_symbol, tls_src))
> > > > {
> > > > set_insn = nullptr;
> > > > break;
> > > > }
> >
> > According to @tls_dynamic_gnu2_64_<mode>, tls_src must be equal to
> > tls_symbol, Do we really need to go through def-use chain to check
> > that?
>
> This verifies that checks the same pseudo register isn't assigned
> to different tls_symbols.
I see.
>
> > We may record the VAL as tls_symbol.
> > > >
> > > > >
> > > > > > + {
> > > > > > + if (DF_REF_IS_ARTIFICIAL (ref))
> > > > > > + break;
> > > > > > +
> > > > > > + set_insn = DF_REF_INSN (ref);
> > > > > > + tls64 = get_attr_tls64 (set_insn);
> > > > > > + if (tls64 != TLS64_LEA)
> > > > > > + {
> > > > > > + set_insn = nullptr;
> > > > > > + break;
> > > > > > + }
> > > > > > +
> > > > > > + rtx tls_set = PATTERN (set_insn);
> > > > > > + if (!tls_src)
> > > > > > + tls_src = SET_SRC (tls_set);
> > > > > > + else if (!rtx_equal_p (tls_src, SET_SRC (tls_set)))
> > > > > > + {
> > > > > > + set_insn = nullptr;
> > > > > > + break;
> > > > > > + }
> > > > > > + }
> > > > > > +
> > > > > > + if (!set_insn)
> > > > > > + return false;
> > > > > > +
> > > > > > + def_insn = set_insn;
> > > > > > + }
> > > > > > + else if (GET_CODE (src) == UNSPEC
> > > > > > + && XINT (src, 1) == UNSPEC_TLSDESC
> > > > > > + && SYMBOL_REF_P (XVECEXP (src, 0, 0)))
> > > > > > + def_insn = nullptr;
> > > > >
> > > > > Similar for here, it's supposed to handle
> > > > > "*tls_dynamic_gnu2_combine_64_<mode>", according to the splitter
> > > > > pattern, the output value can also be CSEd with tls64_call when ever
> > > > > symbol_ref in the second operand of PLUS is the same.
> > > >
> > > > v4 is changed to
> > > >
> > > > rtx tls_symbol = XVECEXP (src, 0, 0);
> > > > src = XVECEXP (src, 0, 1);
> > > > scalar_mode = mode = GET_MODE (src);
> > > > gcc_assert (REG_P (src));
> > >
> > > Since this triggered the assert on
> > >
> > > (set (reg/f:DI 103)
> > > (plus:DI (unspec:DI [
> > > (symbol_ref:DI ("_TLS_MODULE_BASE_") [flags 0x10])
> > > (unspec:DI [
> > > (symbol_ref:DI ("_TLS_MODULE_BASE_") [flags 0x10])
> > > ] UNSPEC_TLSDESC)
> > > (reg/f:DI 7 sp)
> > > ] UNSPEC_TLSDESC)
> > > (const:DI (unspec:DI [
> > > (symbol_ref:DI ("foo") [flags 0x1a] <var_decl
> > > 0x7fffe99dbe40 foo>)
> > > ] UNSPEC_DTPOFF))))
> > >
> > > I added a testcase and kept the v3 code.
> >
> > For tls64 combine, tls_symbol should be second operand of the original src,
> > .i.e
> > (const:DI (unspec:DI [
> > (symbol_ref:DI ("foo") [flags 0x1a] <var_decl
> > 0x7fffe99dbe40 foo>) <--- this
> > ] UNSPEC_DTPOFF))))
> >
> > Not this (symbol_ref:DI ("_TLS_MODULE_BASE_"), and no need for
> > gcc_assert (REG_P (src)).
>
>
> This has been changed to
>
> if (REG_P (src))
> {
> ....
> }
> else if (GET_CODE (src) == UNSPEC
> && XINT (src, 1) == UNSPEC_TLSDESC
> && SYMBOL_REF_P (XVECEXP (src, 0, 0)))
> def_insn = nullptr;
> else
> gcc_unreachable ();
>
> in v5:
>
> https://patchwork.sourceware.org/project/gcc/list/?series=50446
>
>
> H.J.
--
BR,
Hongtao
