riscv/sv.cc

   1 #include "sv.h"
   2 #include "sv_decode.h"
   3
   4 sv_pred_entry* sv_insn_t::get_predentry(uint64_t reg, bool intreg)
   5 {
   6   // okaay so first determine which map to use.  intreg is passed
   7   // in (ultimately) from id_regs.py's examination of the use of
   8   // FRS1/RS1, WRITE_FRD/WRITE_RD, which in turn gets passed
   9   // in from sv_insn_t::fimap...
  10   sv_pred_entry *r;
  11   if (intreg)
  12   {
  13     return &p->get_state()->sv_pred_int_tb[reg];
  14   }
  15   else
  16   {
  17     return &p->get_state()->sv_pred_fp_tb[reg];
  18   }
  19 }
  20
  21 sv_reg_entry* sv_insn_t::get_regentry(uint64_t reg, bool intreg)
  22 {
  23   // okaay so first determine which map to use.  intreg is passed
  24   // in (ultimately) from id_regs.py's examination of the use of
  25   // FRS1/RS1, WRITE_FRD/WRITE_RD, which in turn gets passed
  26   // in from sv_insn_t::fimap...
  27   sv_reg_entry *r;
  28   if (intreg)
  29   {
  30     return &p->get_state()->sv_int_tb[reg];
  31   }
  32   else
  33   {
  34     return &p->get_state()->sv_fp_tb[reg];
  35   }
  36 }
  37
  38 bool sv_insn_t::sv_check_reg(bool intreg, uint64_t reg)
  39 {
  40   sv_reg_entry *r = get_regentry(reg, intreg);
  41   if (r->elwidth != 0)
  42   {
  43     // XXX raise exception
  44   }
  45   if (r->active && r->isvec)
  46   {
  47     fprintf(stderr, "checkreg: %ld active\n", reg);
  48     return true;
  49   }
  50   return false;
  51 }
  52
  53 /* this is the "remap" function.  note that registers can STILL BE REDIRECTED
  54  * yet NOT BE MARKED AS A VECTOR.
  55  *
  56  * reg 5 -> active=false, regidx=XX, isvec=XX     -> returns 5
  57  * reg 5 -> active=true , regidx=35, isvec=false  -> returns 35
  58  * reg 5 -> active=true , regidx=35, isvec=true   -> returns 35 *PLUS LOOP*
  59  *
  60  * so it is possible for example to use the remap system for C  instructions
  61  * to get access to the *full* range of registers x0..x63 (yes 63 because
  62  * SV doubles both the int and fp regfile sizes), by setting
  63  * "active=true, isvec=false" for any of x8..x15
  64  *
  65  * where "active=true, isvec=true" this is the "expected" behaviour
  66  * of SV.  it's "supposed" to "just" be a vectorisation API. it isn't:
  67  * it's quite a bit more.
  68  */
  69 uint64_t sv_insn_t::remap(uint64_t reg, bool intreg, int &voffs)
  70 {
  71   // okaay so first determine which map to use.  intreg is passed
  72   // in (ultimately) from id_regs.py's examination of the use of
  73   // FRS1/RS1, WRITE_FRD/WRITE_RD, which in turn gets passed
  74   // in from sv_insn_t::fimap...
  75   sv_reg_entry *r = get_regentry(reg, intreg);
  76
  77   // next we check if this entry is active.  if not, the register
  78   // is not being "redirected", so just return the actual reg.
  79   if (!r->active)
  80   {
  81     return reg; // not active: return as-is
  82   }
  83   vloop_continue = true;
  84
  85   // next we go through the lookup table.  *THIS* is why the
  86   // sv_reg_entry table is 32 entries (5-bit) *NOT* 6 bits
  87   // the *KEY* (reg) is 5-bit, the *VALUE* (actual target reg) is 6-bit
  88   // XXX TODO: must actually double NXPR and NXFR in processor.h to cope!!
  89   reg = r->regidx;
  90
  91   // now we determine if this is a scalar/vector: if it's scalar
  92   // we return the re-mapped register...
  93   if (!r->isvec) // scalar
  94   {
  95     return reg;
  96   }
  97   vloop_continue = true;
  98
  99   // aaand now, as it's a "vector", FINALLY we can add on the loop-offset
 100   // which was passed in to the sv_insn_t constructor (by reference)
 101   // and, at last, we have "parallelism" a la contiguous registers.
 102   reg += voffs; // wheww :)
 103
 104   return reg;
 105 }
 106
 107 /* gets the predication value (if active).  returns all-1s if not active
 108  * also returns whether zeroing is enabled/disabled for this register.
 109  *
 110  * uses the same sort of lookup logic as remap:
 111  *
 112  * - first thing to note is, there is one CSR table for FP and one for INT
 113  *   (so, FP regs can be predicated separately from INT ones)
 114  * - redirection occurs if the CSR entry for the register is "active".
 115  * - inversion of the predication can be set (so it's possible to have
 116  *   the same actual register value be unchanged yet be referred to by
 117  *   *TWO* redirections, one with inversion, one with not).
 118  *
 119  * note that this function *actually* returns the value of the (integer)
 120  * register file, hence why processor_t has to be passed in
 121  *
 122  * note also that *even scalar* ops will be predicated (i.e. if a register
 123  * has been set active=true and isvec=false in sv_int_tb or sv_fp_tb).
 124  * the way to ensure that scalar ops are not predicated is: set VLEN=0,
 125  * set active=false in sv_int_tb/sv_fp_tb for that register, or switch off
 126  * the predication for that register (sv_pred_int_tb/sv_pred_fb_tb).
 127  *
 128  * note also that the hard limit on SV maximum vector length is actually
 129  * down to the number of bits in the predication i.e. the bitwidth of integer
 130  * registers (i.e. XLEN bits).
 131  */
 132 reg_t sv_insn_t::predicate(uint64_t reg, bool intreg, bool &zeroing)
 133 {
 134   sv_reg_entry *pr = get_regentry(reg, intreg);
 135   if (!pr->active)
 136   {
 137     return ~0x0; // *REGISTER* not active: return all-1s (unconditional "on")
 138   }
 139   sv_pred_entry *r = get_predentry(reg, intreg);
 140   if (!r->active)
 141   {
 142     return ~0x0; // *PREDICATION* not active: return all-1s (unconditional "on")
 143   }
 144   zeroing = r->zero;
 145   reg = r->regidx;
 146   reg_t predicate = READ_REG(reg); // macros go through processor_t state
 147   if (r->inv)
 148   {
 149     return ~predicate;
 150   }
 151   return predicate;
 152 }
 153
 154 uint64_t sv_insn_t::predicated(uint64_t reg, int offs, uint64_t pred)
 155 {
 156     if (pred & (1<<offs))
 157     {
 158         return reg;
 159     }
 160     fprintf(stderr, "predication %ld %d %lx\n", reg, offs, pred);
 161     return 0;
 162 }
 163
 164 bool sv_insn_t::stop_vloop(void)
 165 {
 166     return (p->get_state()->vl == 0) || !vloop_continue;
 167 }
 168
 169