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Re: [PATCH v2 20/22] tcg/arm: Implement direct branch for goto_tb
From: |
Alex Bennée |
Subject: |
Re: [PATCH v2 20/22] tcg/arm: Implement direct branch for goto_tb |
Date: |
Tue, 17 Jan 2023 18:33:24 +0000 |
User-agent: |
mu4e 1.9.15; emacs 29.0.60 |
Richard Henderson <richard.henderson@linaro.org> writes:
> Now that tcg can handle direct and indirect goto_tb
> simultaneously, we can optimistically leave space for
> a direct branch and fall back to loading the pointer
> from the TB for an indirect branch.
>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
> tcg/arm/tcg-target.c.inc | 52 ++++++++++++++++++++++++++++------------
> 1 file changed, 37 insertions(+), 15 deletions(-)
>
> diff --git a/tcg/arm/tcg-target.c.inc b/tcg/arm/tcg-target.c.inc
> index e1e1c2620d..794ed8c3a2 100644
> --- a/tcg/arm/tcg-target.c.inc
> +++ b/tcg/arm/tcg-target.c.inc
> @@ -135,6 +135,8 @@ typedef enum {
> ARITH_BIC = 0xe << 21,
> ARITH_MVN = 0xf << 21,
>
> + INSN_B = 0x0a000000,
> +
> INSN_CLZ = 0x016f0f10,
> INSN_RBIT = 0x06ff0f30,
>
> @@ -546,7 +548,7 @@ static bool tcg_target_const_match(int64_t val, TCGType
> type, int ct)
>
> static void tcg_out_b_imm(TCGContext *s, ARMCond cond, int32_t offset)
> {
> - tcg_out32(s, (cond << 28) | 0x0a000000 |
> + tcg_out32(s, (cond << 28) | INSN_B |
> (((offset - 8) >> 2) & 0x00ffffff));
deposit32?
> }
>
> @@ -1941,32 +1943,52 @@ static void tcg_out_exit_tb(TCGContext *s, uintptr_t
> arg)
>
> static void tcg_out_goto_tb(TCGContext *s, int which)
> {
> - /* Indirect jump method */
> - intptr_t ptr, dif, dil;
> - TCGReg base = TCG_REG_PC;
> + uintptr_t i_addr;
> + intptr_t i_disp;
>
> - ptr = get_jmp_target_addr(s, which);
> - dif = tcg_pcrel_diff(s, (void *)ptr) - 8;
> - dil = sextract32(dif, 0, 12);
> - if (dif != dil) {
> + /* Direct branch will be patched by tb_target_set_jmp_target. */
> + set_jmp_insn_offset(s, which);
> + tcg_out32(s, INSN_NOP);
> +
> + /* When branch is out of range, fall through to indirect. */
> + i_addr = get_jmp_target_addr(s, which);
> + i_disp = tcg_pcrel_diff(s, (void *)i_addr) - 8;
> + tcg_debug_assert(i_disp < 0);
> + if (i_disp >= -0xfff) {
> + tcg_out_ld32_12(s, COND_AL, TCG_REG_PC, TCG_REG_PC, i_disp);
> + } else {
> /*
> * The TB is close, but outside the 12 bits addressable by
> * the load. We can extend this to 20 bits with a sub of a
> - * shifted immediate from pc. In the vastly unlikely event
> - * the code requires more than 1MB, we'll use 2 insns and
> - * be no worse off.
> + * shifted immediate from pc.
> */
> - base = TCG_REG_R0;
> - tcg_out_movi32(s, COND_AL, base, ptr - dil);
> + int h = -i_disp;
> + int l = h & 0xfff;
> +
> + h = encode_imm_nofail(h - l);
> + tcg_out_dat_imm(s, COND_AL, ARITH_SUB, TCG_REG_R0, TCG_REG_PC, h);
> + tcg_out_ld32_12(s, COND_AL, TCG_REG_PC, TCG_REG_R0, l);
> }
> - tcg_out_ld32_12(s, COND_AL, TCG_REG_PC, base, dil);
> set_jmp_reset_offset(s, which);
> }
>
> void tb_target_set_jmp_target(const TranslationBlock *tb, int n,
> uintptr_t jmp_rx, uintptr_t jmp_rw)
> {
> - /* Always indirect, nothing to do */
> + uintptr_t addr = tb->jmp_target_addr[n];
> + ptrdiff_t offset = addr - (jmp_rx + 8);
> + tcg_insn_unit insn;
> +
> + /* Either directly branch, or fall through to indirect branch. */
> + if (offset == sextract64(offset, 0, 26)) {
> + /* B <addr> */
> + insn = (COND_AL << 28) | INSN_B | ((offset >> 2) &
> 0x00ffffff);
deposit32
> + } else {
> + insn = INSN_NOP;
> + }
> +
> + qatomic_set((uint32_t *)jmp_rw, insn);
> + flush_idcache_range(jmp_rx, jmp_rw, 4);
> }
>
> static void tcg_out_op(TCGContext *s, TCGOpcode opc,
Otherwise:
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
--
Alex Bennée
Virtualisation Tech Lead @ Linaro
- Re: [PATCH v2 13/22] tcg: Move tb_target_set_jmp_target declaration to tcg.h, (continued)
- [PATCH v2 16/22] tcg/aarch64: Reorg goto_tb implementation, Richard Henderson, 2023/01/08
- [PATCH v2 17/22] tcg/ppc: Reorg goto_tb implementation, Richard Henderson, 2023/01/08
- [PATCH v2 18/22] tcg/sparc64: Remove USE_REG_TB, Richard Henderson, 2023/01/08
- [PATCH v2 19/22] tcg/sparc64: Reorg goto_tb implementation, Richard Henderson, 2023/01/08
- [PATCH v2 20/22] tcg/arm: Implement direct branch for goto_tb, Richard Henderson, 2023/01/08
- Re: [PATCH v2 20/22] tcg/arm: Implement direct branch for goto_tb,
Alex Bennée <=
- [PATCH v2 21/22] tcg/riscv: Introduce OPC_NOP, Richard Henderson, 2023/01/08
- [PATCH v2 22/22] tcg/riscv: Implement direct branch for goto_tb, Richard Henderson, 2023/01/08
- Re: [PATCH v2 00/22] tcg: exit_tb tidy, goto_tb reorg, Richard Henderson, 2023/01/14