Re: [Qemu-devel] [PATCH 23/23] target-sparc: Optimize conditionals using SUBCC

[Aurelien Jarno]

This patch breaks the boot of a linux sparc64 kernel very early in the
boot process. The boot hangs after:

| OpenBIOS for Sparc64
| Configuration device id QEMU version 1 machine id 0
| kernel addr 404000 size 5be6b8
| kernel cmdline root=/dev/vda4 console=ttyS0
| CPUs: 1 x SUNW,UltraSPARC-IIi
| UUID: 00000000-0000-0000-0000-000000000000
| Welcome to OpenBIOS v1.0 built on Aug 19 2012 13:06
|   Type 'help' for detailed information
| [sparc64] Kernel already loaded
| 
| [    0.000000] PROMLIB: Sun IEEE Boot Prom 'OBP 3.10.24 1999/01/01 01:01'
| [    0.000000] PROMLIB: Root node compatible: sun4u
| [    0.000000] Initializing cgroup subsys cpuset
| [    0.000000] Initializing cgroup subsys cpu
| [    0.000000] Linux version 3.2.0-3-sparc64 (Debian 3.2.23-1) 
(address@hidden) (gcc version 4.6.3 (Debian 4.6.3-5) ) #1 Fri Aug 3 15:37:15 
UTC 2012
| [    0.000000] bootconsole [earlyprom0] enabled
| [    0.000000] ARCH: SUN4U
| [    0.000000] Ethernet address: 52:54:00:12:34:56
| [    0.000000] Kernel: Using 2 locked TLB entries for main kernel image.
| [    0.000000] Remapping the kernel... done.
| [    0.000000] OF stdout device is: /address@hidden,0/address@hidden/su
| [    0.000000] PROM: Built device tree with 32122 bytes of memory.


On Fri, Oct 05, 2012 at 04:55:10PM -0700, Richard Henderson wrote:
> Aka "normal" comparisons.  We now have the infrastructure to
> pass back non-boolean results from gen_compare.  This will
> automatically get used by both branches and conditional moves.
> 
> Signed-off-by: Richard Henderson <address@hidden>
> ---
>  target-sparc/translate.c | 192 
> ++++++++++++++++++++++++++++++++---------------
>  1 file changed, 131 insertions(+), 61 deletions(-)
> 
> diff --git a/target-sparc/translate.c b/target-sparc/translate.c
> index a7f6407..472eb51 100644
> --- a/target-sparc/translate.c
> +++ b/target-sparc/translate.c
> @@ -1046,83 +1046,153 @@ static void free_compare(DisasCompare *cmp)
>      }
>  }
>  
> -static void gen_compare(DisasCompare *cmp, unsigned int cc, unsigned int 
> cond,
> +static void gen_compare(DisasCompare *cmp, bool xcc, unsigned int cond,
>                          DisasContext *dc)
>  {
> +    static int subcc_cond[16] = {
> +        -1, /* never */
> +        TCG_COND_EQ,
> +        TCG_COND_LE,
> +        TCG_COND_LT,
> +        TCG_COND_LEU,
> +        TCG_COND_LTU,
> +        -1, /* neg */
> +        -1, /* overflow */
> +        -1, /* always */
> +        TCG_COND_NE,
> +        TCG_COND_GT,
> +        TCG_COND_GE,
> +        TCG_COND_GTU,
> +        TCG_COND_GEU,
> +        -1, /* pos */
> +        -1, /* no overflow */
> +    };
> +
>      TCGv_i32 r_src;
>      TCGv r_dst;
>  
> -    /* For now we still generate a straight boolean result.  */
> -    cmp->cond = TCG_COND_NE;
> -    cmp->is_bool = true;
> -    cmp->g1 = cmp->g2 = false;
> -    cmp->c1 = r_dst = tcg_temp_new();
> -    cmp->c2 = tcg_const_tl(0);
> -
>  #ifdef TARGET_SPARC64
> -    if (cc)
> +    if (xcc) {
>          r_src = cpu_xcc;
> -    else
> +    } else {
>          r_src = cpu_psr;
> +    }
>  #else
>      r_src = cpu_psr;
>  #endif
> +
>      switch (dc->cc_op) {
> -    case CC_OP_FLAGS:
> +    case CC_OP_SUB:
> +        switch (cond) {
> +        case 6:  /* neg */
> +        case 14: /* pos */
> +            cmp->cond = (cond == 6 ? TCG_COND_LT : TCG_COND_GE);
> +            cmp->is_bool = false;
> +            cmp->g2 = false;
> +            cmp->c2 = tcg_const_tl(0);
> +#ifdef TARGET_SPARC64
> +            if (!xcc) {
> +                cmp->g1 = false;
> +                cmp->c1 = tcg_temp_new();
> +                tcg_gen_ext32s_tl(cmp->c1, cpu_cc_dst);
> +                break;
> +            }
> +#endif
> +            cmp->g1 = true;
> +            cmp->c1 = cpu_cc_dst;
> +            break;
> +
> +        case 0: /* never */
> +        case 8: /* always */
> +        case 7: /* overflow */
> +        case 15: /* !overflow */
> +            goto do_dynamic;
> +
> +        default:
> +            cmp->cond = subcc_cond[cond];
> +            cmp->is_bool = false;
> +#ifdef TARGET_SPARC64
> +            if (!xcc) {
> +                /* Note that sign-extension works for unsigned compares as
> +                   long as both operands are sign-extended.  */
> +                cmp->g1 = cmp->g2 = false;
> +                cmp->c1 = tcg_temp_new();
> +                cmp->c2 = tcg_temp_new();
> +                tcg_gen_ext32s_tl(cmp->c1, cpu_cc_src);
> +                tcg_gen_ext32s_tl(cmp->c2, cpu_cc_src2);
> +            }
> +#endif
> +            cmp->g1 = cmp->g2 = true;
> +            cmp->c1 = cpu_cc_src;
> +            cmp->c2 = cpu_cc_src2;
> +            break;
> +        }
>          break;
> +
>      default:
> +    do_dynamic:
>          gen_helper_compute_psr(cpu_env);
>          dc->cc_op = CC_OP_FLAGS;
> -        break;
> -    }
> -    switch (cond) {
> -    case 0x0:
> -        gen_op_eval_bn(r_dst);
> -        break;
> -    case 0x1:
> -        gen_op_eval_be(r_dst, r_src);
> -        break;
> -    case 0x2:
> -        gen_op_eval_ble(r_dst, r_src);
> -        break;
> -    case 0x3:
> -        gen_op_eval_bl(r_dst, r_src);
> -        break;
> -    case 0x4:
> -        gen_op_eval_bleu(r_dst, r_src);
> -        break;
> -    case 0x5:
> -        gen_op_eval_bcs(r_dst, r_src);
> -        break;
> -    case 0x6:
> -        gen_op_eval_bneg(r_dst, r_src);
> -        break;
> -    case 0x7:
> -        gen_op_eval_bvs(r_dst, r_src);
> -        break;
> -    case 0x8:
> -        gen_op_eval_ba(r_dst);
> -        break;
> -    case 0x9:
> -        gen_op_eval_bne(r_dst, r_src);
> -        break;
> -    case 0xa:
> -        gen_op_eval_bg(r_dst, r_src);
> -        break;
> -    case 0xb:
> -        gen_op_eval_bge(r_dst, r_src);
> -        break;
> -    case 0xc:
> -        gen_op_eval_bgu(r_dst, r_src);
> -        break;
> -    case 0xd:
> -        gen_op_eval_bcc(r_dst, r_src);
> -        break;
> -    case 0xe:
> -        gen_op_eval_bpos(r_dst, r_src);
> -        break;
> -    case 0xf:
> -        gen_op_eval_bvc(r_dst, r_src);
> +        /* FALLTHRU */
> +
> +    case CC_OP_FLAGS:
> +        /* We're going to generate a boolean result.  */
> +        cmp->cond = TCG_COND_NE;
> +        cmp->is_bool = true;
> +        cmp->g1 = cmp->g2 = false;
> +        cmp->c1 = r_dst = tcg_temp_new();
> +        cmp->c2 = tcg_const_tl(0);
> +
> +        switch (cond) {
> +        case 0x0:
> +            gen_op_eval_bn(r_dst);
> +            break;
> +        case 0x1:
> +            gen_op_eval_be(r_dst, r_src);
> +            break;
> +        case 0x2:
> +            gen_op_eval_ble(r_dst, r_src);
> +            break;
> +        case 0x3:
> +            gen_op_eval_bl(r_dst, r_src);
> +            break;
> +        case 0x4:
> +            gen_op_eval_bleu(r_dst, r_src);
> +            break;
> +        case 0x5:
> +            gen_op_eval_bcs(r_dst, r_src);
> +            break;
> +        case 0x6:
> +            gen_op_eval_bneg(r_dst, r_src);
> +            break;
> +        case 0x7:
> +            gen_op_eval_bvs(r_dst, r_src);
> +            break;
> +        case 0x8:
> +            gen_op_eval_ba(r_dst);
> +            break;
> +        case 0x9:
> +            gen_op_eval_bne(r_dst, r_src);
> +            break;
> +        case 0xa:
> +            gen_op_eval_bg(r_dst, r_src);
> +            break;
> +        case 0xb:
> +            gen_op_eval_bge(r_dst, r_src);
> +            break;
> +        case 0xc:
> +            gen_op_eval_bgu(r_dst, r_src);
> +            break;
> +        case 0xd:
> +            gen_op_eval_bcc(r_dst, r_src);
> +            break;
> +        case 0xe:
> +            gen_op_eval_bpos(r_dst, r_src);
> +            break;
> +        case 0xf:
> +            gen_op_eval_bvc(r_dst, r_src);
> +            break;
> +        }
>          break;
>      }
>  }
> -- 
> 1.7.11.4
> 
> 

-- 
Aurelien Jarno                          GPG: 1024D/F1BCDB73
address@hidden                 http://www.aurel32.net