On Tue, Aug 12, 2025 at 06:47:54AM -0700, H.J. Lu wrote:
> On Mon, Aug 11, 2025 at 11:13 PM Hongtao Liu <crazy...@gmail.com> wrote:
> >
> > 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.
>
> Before RA, hard registers are only used as scratch registers:
>
> insn 20 set rax ....
> insn 21 set r300 rax # rax is dead after this.
>
> Now we are inserting another rax usage in the same basic block.
>
> set rax ...
> set r400 rax
>
> we must insert them where rax isn't alive. We can't insert them
> between insn 20 and insn 21. My patch inserts them where all
> caller-saved registers are dead.
gcc.target/i386/pr81501-4a.c is an example. We want to insert
(call_insn/u 81 74 4 2 (parallel [
(set (reg:DI 0 ax)
(call:DI (mem:QI (symbol_ref:DI ("__tls_get_addr")) [0 S1 A8])
(const_int 0 [0])))
(unspec:DI [
(symbol_ref:DI ("foo") [flags 0x10] <var_decl
0x7fb4f0dd6e40 foo>)
(reg/f:DI 7 sp)
] UNSPEC_TLS_GD)
(clobber (reg:DI 5 di))
]) "pr81501-4a.c":26:1 1657 {*tls_global_dynamic_64_di}
(expr_list:REG_EH_REGION (const_int -2147483648 [0xffffffff80000000])
(nil))
(nil))
in a basic block with
(note 7 0 73 2 [bb 2] NOTE_INSN_BASIC_BLOCK)
(insn 73 7 74 2 (set (reg:SI 117 [ n ])
(reg:SI 5 di [ n ])) "pr81501-4a.c":26:1 100 {*movsi_internal}
(expr_list:REG_DEAD (reg:SI 5 di [ n ])
(nil)))
(insn 74 73 4 2 (set (reg/f:DI 118 [ caller_foop ])
(reg:DI 4 si [ caller_foop ])) "pr81501-4a.c":26:1 99 {*movdi_internal}
(expr_list:REG_DEAD (reg:DI 4 si [ caller_foop ])
(nil)))
(note 4 74 9 2 NOTE_INSN_FUNCTION_BEG)
(insn 9 4 10 2 (set (reg/f:DI 105)
(symbol_ref/f:DI ("*.LC0") [flags 0x2] <var_decl 0x7fffe99fb5f0
*.LC0>)) "pr81501-4a.c":30:3 99 {*movdi_internal}
(nil))
(insn 10 9 11 2 (set (reg:DI 5 di)
(reg/f:DI 105)) "pr81501-4a.c":30:3 99 {*movdi_internal}
(expr_list:REG_DEAD (reg/f:DI 105)
(expr_list:REG_EQUAL (symbol_ref/f:DI ("*.LC0") [flags 0x2] <var_decl
0x7fffe99fb5f0 *.LC0>)
(nil))))
(call_insn 11 10 12 2 (call (mem:QI (symbol_ref:DI ("bar3") [flags 0x41]
<function_decl 0x7fffe99cdb00 bar3>) [0 bar3 S1 A8])
(const_int 0 [0])) "pr81501-4a.c":30:3 1469 {*call}
(expr_list:REG_DEAD (reg:DI 5 di)
(expr_list:REG_CALL_DECL (symbol_ref:DI ("bar3") [flags 0x41]
<function_decl 0x7fffe99cdb00 bar3>)
(nil)))
(expr_list:DI (use (reg:DI 5 di))
(nil)))
We must place it after both RAX and RDI are dead, which is after
(insn 74 73 4 2 (set (reg/f:DI 118 [ caller_foop ])
(reg:DI 4 si [ caller_foop ])) "pr81501-4a.c":26:1 99 {*movdi_internal}
(expr_list:REG_DEAD (reg:DI 4 si [ caller_foop ])
(nil)))
H.J.
