Re: [Qemu-devel] [PATCH 11/15] tcg-mips: Use mips64r6 instructions in tcg_out_movi

[James Hogan <james.hogan@imgtec.com>]

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Hi Richard,

On Tue, Feb 09, 2016 at 09:39:59PM +1100, Richard Henderson wrote:
> The DAHI and DATI instructions can eliminate two insns
> off the pre-r6 path.
> 
> Signed-off-by: Richard Henderson <rth@twiddle.net>
> ---
>  tcg/mips/tcg-target.c | 63 +++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 63 insertions(+)
> 
> diff --git a/tcg/mips/tcg-target.c b/tcg/mips/tcg-target.c
> index 97f9251..f7f4331 100644
> --- a/tcg/mips/tcg-target.c
> +++ b/tcg/mips/tcg-target.c
> @@ -303,7 +303,9 @@ typedef enum {
>      OPC_ORI      = 015 << 26,
>      OPC_XORI     = 016 << 26,
>      OPC_LUI      = 017 << 26,
> +    OPC_AUI      = OPC_LUI,
>      OPC_DADDIU   = 031 << 26,
> +    OPC_DAUI     = 035 << 26,
>      OPC_LB       = 040 << 26,
>      OPC_LH       = 041 << 26,
>      OPC_LW       = 043 << 26,
> @@ -383,6 +385,8 @@ typedef enum {
>      OPC_REGIMM   = 001 << 26,
>      OPC_BLTZ     = OPC_REGIMM | (000 << 16),
>      OPC_BGEZ     = OPC_REGIMM | (001 << 16),
> +    OPC_DAHI     = OPC_REGIMM | (006 << 16),
> +    OPC_DATI     = OPC_REGIMM | (036 << 16),
>  
>      OPC_SPECIAL2 = 034 << 26,
>      OPC_MUL_R5   = OPC_SPECIAL2 | 002,
> @@ -402,6 +406,10 @@ typedef enum {
>      OPC_SEB      = OPC_SPECIAL3 | 02040,
>      OPC_SEH      = OPC_SPECIAL3 | 03040,
>  
> +    OPC_PCREL    = 073 << 26,
> +    OPC_ADDIUPC  = OPC_PCREL | (0 << 19),
> +    OPC_ALUIPC   = OPC_PCREL | (3 << 19) | (7 << 16),
> +
>      /* MIPS r6 doesn't have JR, JALR should be used instead */
>      OPC_JR       = use_mips32r6_instructions ? OPC_JALR : OPC_JR_R5,
>  
> @@ -448,6 +456,17 @@ static inline void tcg_out_opc_imm(TCGContext *s, MIPSInsn opc,
>      tcg_out32(s, inst);
>  }
>  
> +static inline void tcg_out_opc_pc19(TCGContext *s, MIPSInsn opc,
> +                                    TCGReg rs, TCGArg imm)
> +{
> +    int32_t inst;
> +
> +    inst = opc;
> +    inst |= (rs & 0x1F) << 21;
> +    inst |= (imm & 0x7ffff);
> +    tcg_out32(s, inst);
> +}
> +
>  /*
>   * Type bitfield
>   */
> @@ -589,6 +608,50 @@ static void tcg_out_movi(TCGContext *s, TCGType type,
>      }
>      if (TCG_TARGET_REG_BITS == 32 || arg == (int32_t)arg) {
>          tcg_out_opc_imm(s, OPC_LUI, ret, TCG_REG_ZERO, arg >> 16);
> +    } else if (use_mips32r6_instructions) {
> +        tcg_target_long disp = arg - (intptr_t)s->code_ptr;
> +        if (disp == sextract32(disp, 2, 19) * 4) {
> +            tcg_out_opc_pc19(s, OPC_ADDIUPC, ret, disp >> 2);
> +            return;
> +        } else if ((disp & ~(tcg_target_long)0xffff)
> +                   == sextract32(disp, 16, 16) * 0x10000) {
> +            tcg_out_opc_imm(s, OPC_ALUIPC, ret, 0, disp >> 16);

I think ret and 0 are the wrong way around here. You're putting 0 in rs
(the destination register), which causes a seg fault.

OUT: [size=56] 
0xfff30b0064:  lw       s1,-8(s0) 
0xfff30b0068:  bnezalc  zero,s1,0xfff30b0090 
0xfff30b006c:  nop 
0xfff30b0070:  j        0xfff0000000 
0xfff30b0074:  nop 
0xfff30b0078:  lui      s1,0xbfc0 
0xfff30b007c:  ori      s1,s1,0x580 
0xfff30b0080:  sd       s1,256(s0) 
0xfff30b0084:  aluipc   zero,0xfeb7 
0xfff30b0088:  j        0xfff30b0034 
0xfff30b008c:  ori      v0,v0,0x4010 
0xfff30b0090:  aluipc   zero,0xfeb7 
0xfff30b0094:  j        0xfff30b0034 
0xfff30b0098:  ori      v0,v0,0x4013

Cheers
James



> +        } else {
> +            TCGReg in = TCG_REG_ZERO;
> +            tcg_target_long tmp = (int16_t)arg;
> +
> +            /* The R6 manual recommends construction of immediates in
> +               order of low to high (ADDI, AUI, DAHI, DATI) in order
> +               to simplify hardware recognizing these sequences.  */
> +
> +            if (tmp) {
> +                tcg_out_opc_imm(s, OPC_ADDIU, ret, in, tmp);
> +                in = ret;
> +            }
> +            arg = (arg - tmp) >> 16;
> +            tmp = (int16_t)arg;
> +
> +            /* Note that DAHI and DATI only have one register operand,
> +               and are thus we must put a zero low part in place.  Also
> +               note that we already eliminated simple 32-bit constants
> +               so we know this must happen.  */
> +            if (tmp || in != ret) {
> +                tcg_out_opc_imm(s, OPC_AUI, ret, in, tmp);
> +            }
> +            arg = (arg - tmp) >> 16;
> +            tmp = (int16_t)arg;
> +
> +            if (tmp) {
> +                tcg_out_opc_imm(s, OPC_DAHI, ret, 0, tmp);
> +            }
> +            arg = (arg - tmp) >> 16;
> +            tcg_debug_assert(arg == (int16_t)arg);
> +
> +            if (arg) {
> +                tcg_out_opc_imm(s, OPC_DATI, ret, 0, arg);
> +            }
> +            return;
> +        }
>      } else {
>          tcg_out_movi(s, TCG_TYPE_I32, ret, arg >> 31 >> 1);
>          if (arg & 0xffff0000ull) {
> -- 
> 2.5.0
> 

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