nir/vtn: SPIR-V bit count opcodes (core and extension) dest size mismatches nir
[mesa.git] / src / compiler / spirv / vtn_alu.c
index 6d4347887cdc1b8f6ab538abf43cc4a44266006e..b403a25e51b20659bc22b13fc61f32a73355427e 100644 (file)
@@ -43,7 +43,7 @@ wrap_matrix(struct vtn_builder *b, struct vtn_ssa_value *val)
       return val;
 
    struct vtn_ssa_value *dest = rzalloc(b, struct vtn_ssa_value);
-   dest->type = val->type;
+   dest->type = glsl_get_bare_type(val->type);
    dest->elems = ralloc_array(b, struct vtn_ssa_value *, 1);
    dest->elems[0] = val;
 
@@ -153,48 +153,46 @@ mat_times_scalar(struct vtn_builder *b,
    return dest;
 }
 
-static void
+static struct vtn_ssa_value *
 vtn_handle_matrix_alu(struct vtn_builder *b, SpvOp opcode,
-                      struct vtn_value *dest,
                       struct vtn_ssa_value *src0, struct vtn_ssa_value *src1)
 {
    switch (opcode) {
    case SpvOpFNegate: {
-      dest->ssa = vtn_create_ssa_value(b, src0->type);
+      struct vtn_ssa_value *dest = vtn_create_ssa_value(b, src0->type);
       unsigned cols = glsl_get_matrix_columns(src0->type);
       for (unsigned i = 0; i < cols; i++)
-         dest->ssa->elems[i]->def = nir_fneg(&b->nb, src0->elems[i]->def);
-      break;
+         dest->elems[i]->def = nir_fneg(&b->nb, src0->elems[i]->def);
+      return dest;
    }
 
    case SpvOpFAdd: {
-      dest->ssa = vtn_create_ssa_value(b, src0->type);
+      struct vtn_ssa_value *dest = vtn_create_ssa_value(b, src0->type);
       unsigned cols = glsl_get_matrix_columns(src0->type);
       for (unsigned i = 0; i < cols; i++)
-         dest->ssa->elems[i]->def =
+         dest->elems[i]->def =
             nir_fadd(&b->nb, src0->elems[i]->def, src1->elems[i]->def);
-      break;
+      return dest;
    }
 
    case SpvOpFSub: {
-      dest->ssa = vtn_create_ssa_value(b, src0->type);
+      struct vtn_ssa_value *dest = vtn_create_ssa_value(b, src0->type);
       unsigned cols = glsl_get_matrix_columns(src0->type);
       for (unsigned i = 0; i < cols; i++)
-         dest->ssa->elems[i]->def =
+         dest->elems[i]->def =
             nir_fsub(&b->nb, src0->elems[i]->def, src1->elems[i]->def);
-      break;
+      return dest;
    }
 
    case SpvOpTranspose:
-      dest->ssa = vtn_ssa_transpose(b, src0);
-      break;
+      return vtn_ssa_transpose(b, src0);
 
    case SpvOpMatrixTimesScalar:
       if (src0->transposed) {
-         dest->ssa = vtn_ssa_transpose(b, mat_times_scalar(b, src0->transposed,
-                                                           src1->def));
+         return vtn_ssa_transpose(b, mat_times_scalar(b, src0->transposed,
+                                                         src1->def));
       } else {
-         dest->ssa = mat_times_scalar(b, src0, src1->def);
+         return mat_times_scalar(b, src0, src1->def);
       }
       break;
 
@@ -202,9 +200,9 @@ vtn_handle_matrix_alu(struct vtn_builder *b, SpvOp opcode,
    case SpvOpMatrixTimesVector:
    case SpvOpMatrixTimesMatrix:
       if (opcode == SpvOpVectorTimesMatrix) {
-         dest->ssa = matrix_multiply(b, vtn_ssa_transpose(b, src1), src0);
+         return matrix_multiply(b, vtn_ssa_transpose(b, src1), src0);
       } else {
-         dest->ssa = matrix_multiply(b, src0, src1);
+         return matrix_multiply(b, src0, src1);
       }
       break;
 
@@ -259,7 +257,21 @@ vtn_nir_alu_op_for_spirv_opcode(struct vtn_builder *b,
    case SpvOpBitFieldSExtract:      return nir_op_ibitfield_extract;
    case SpvOpBitFieldUExtract:      return nir_op_ubitfield_extract;
    case SpvOpBitReverse:            return nir_op_bitfield_reverse;
-   case SpvOpBitCount:              return nir_op_bit_count;
+
+   case SpvOpUCountLeadingZerosINTEL: return nir_op_uclz;
+   /* SpvOpUCountTrailingZerosINTEL is handled elsewhere. */
+   case SpvOpAbsISubINTEL:          return nir_op_uabs_isub;
+   case SpvOpAbsUSubINTEL:          return nir_op_uabs_usub;
+   case SpvOpIAddSatINTEL:          return nir_op_iadd_sat;
+   case SpvOpUAddSatINTEL:          return nir_op_uadd_sat;
+   case SpvOpIAverageINTEL:         return nir_op_ihadd;
+   case SpvOpUAverageINTEL:         return nir_op_uhadd;
+   case SpvOpIAverageRoundedINTEL:  return nir_op_irhadd;
+   case SpvOpUAverageRoundedINTEL:  return nir_op_urhadd;
+   case SpvOpISubSatINTEL:          return nir_op_isub_sat;
+   case SpvOpUSubSatINTEL:          return nir_op_usub_sat;
+   case SpvOpIMul32x16INTEL:        return nir_op_imul_32x16;
+   case SpvOpUMul32x16INTEL:        return nir_op_umul_32x16;
 
    /* The ordered / unordered operators need special implementation besides
     * the logical operator to use since they also need to check if operands are
@@ -268,8 +280,9 @@ vtn_nir_alu_op_for_spirv_opcode(struct vtn_builder *b,
    case SpvOpFOrdEqual:                            return nir_op_feq;
    case SpvOpFUnordEqual:                          return nir_op_feq;
    case SpvOpINotEqual:                            return nir_op_ine;
-   case SpvOpFOrdNotEqual:                         return nir_op_fne;
-   case SpvOpFUnordNotEqual:                       return nir_op_fne;
+   case SpvOpLessOrGreater:                        /* Deprecated, use OrdNotEqual */
+   case SpvOpFOrdNotEqual:                         return nir_op_fneu;
+   case SpvOpFUnordNotEqual:                       return nir_op_fneu;
    case SpvOpULessThan:                            return nir_op_ult;
    case SpvOpSLessThan:                            return nir_op_ilt;
    case SpvOpFOrdLessThan:                         return nir_op_flt;
@@ -340,6 +353,9 @@ vtn_nir_alu_op_for_spirv_opcode(struct vtn_builder *b,
    case SpvOpDPdxCoarse:   return nir_op_fddx_coarse;
    case SpvOpDPdyCoarse:   return nir_op_fddy_coarse;
 
+   case SpvOpIsNormal:     return nir_op_fisnormal;
+   case SpvOpIsFinite:     return nir_op_fisfinite;
+
    default:
       vtn_fail("No NIR equivalent: %u", opcode);
    }
@@ -377,15 +393,32 @@ handle_rounding_mode(struct vtn_builder *b, struct vtn_value *val, int member,
    }
 }
 
+static void
+handle_no_wrap(struct vtn_builder *b, struct vtn_value *val, int member,
+               const struct vtn_decoration *dec, void *_alu)
+{
+   nir_alu_instr *alu = _alu;
+   switch (dec->decoration) {
+   case SpvDecorationNoSignedWrap:
+      alu->no_signed_wrap = true;
+      break;
+   case SpvDecorationNoUnsignedWrap:
+      alu->no_unsigned_wrap = true;
+      break;
+   default:
+      /* Do nothing. */
+      break;
+   }
+}
+
 void
 vtn_handle_alu(struct vtn_builder *b, SpvOp opcode,
                const uint32_t *w, unsigned count)
 {
-   struct vtn_value *val = vtn_push_value(b, w[2], vtn_value_type_ssa);
-   const struct glsl_type *type =
-      vtn_value(b, w[1], vtn_value_type_type)->type->type;
+   struct vtn_value *dest_val = vtn_untyped_value(b, w[2]);
+   const struct glsl_type *dest_type = vtn_get_type(b, w[1])->type;
 
-   vtn_foreach_decoration(b, val, handle_no_contraction, NULL);
+   vtn_foreach_decoration(b, dest_val, handle_no_contraction, NULL);
 
    /* Collect the various SSA sources */
    const unsigned num_inputs = count - 3;
@@ -395,12 +428,13 @@ vtn_handle_alu(struct vtn_builder *b, SpvOp opcode,
 
    if (glsl_type_is_matrix(vtn_src[0]->type) ||
        (num_inputs >= 2 && glsl_type_is_matrix(vtn_src[1]->type))) {
-      vtn_handle_matrix_alu(b, opcode, val, vtn_src[0], vtn_src[1]);
+      vtn_push_ssa_value(b, w[2],
+         vtn_handle_matrix_alu(b, opcode, vtn_src[0], vtn_src[1]));
       b->nb.exact = b->exact;
       return;
    }
 
-   val->ssa = vtn_create_ssa_value(b, type);
+   struct vtn_ssa_value *dest = vtn_create_ssa_value(b, dest_type);
    nir_ssa_def *src[4] = { NULL, };
    for (unsigned i = 0; i < num_inputs; i++) {
       vtn_assert(glsl_type_is_vector_or_scalar(vtn_src[i]->type));
@@ -409,107 +443,91 @@ vtn_handle_alu(struct vtn_builder *b, SpvOp opcode,
 
    switch (opcode) {
    case SpvOpAny:
-      if (src[0]->num_components == 1) {
-         val->ssa->def = nir_imov(&b->nb, src[0]);
-      } else {
-         nir_op op;
-         switch (src[0]->num_components) {
-         case 2:  op = nir_op_bany_inequal2; break;
-         case 3:  op = nir_op_bany_inequal3; break;
-         case 4:  op = nir_op_bany_inequal4; break;
-         default: vtn_fail("invalid number of components");
-         }
-         val->ssa->def = nir_build_alu(&b->nb, op, src[0],
-                                       nir_imm_false(&b->nb),
-                                       NULL, NULL);
-      }
+      dest->def = nir_bany(&b->nb, src[0]);
       break;
 
    case SpvOpAll:
-      if (src[0]->num_components == 1) {
-         val->ssa->def = nir_imov(&b->nb, src[0]);
-      } else {
-         nir_op op;
-         switch (src[0]->num_components) {
-         case 2:  op = nir_op_ball_iequal2;  break;
-         case 3:  op = nir_op_ball_iequal3;  break;
-         case 4:  op = nir_op_ball_iequal4;  break;
-         default: vtn_fail("invalid number of components");
-         }
-         val->ssa->def = nir_build_alu(&b->nb, op, src[0],
-                                       nir_imm_true(&b->nb),
-                                       NULL, NULL);
-      }
+      dest->def = nir_ball(&b->nb, src[0]);
       break;
 
    case SpvOpOuterProduct: {
       for (unsigned i = 0; i < src[1]->num_components; i++) {
-         val->ssa->elems[i]->def =
+         dest->elems[i]->def =
             nir_fmul(&b->nb, src[0], nir_channel(&b->nb, src[1], i));
       }
       break;
    }
 
    case SpvOpDot:
-      val->ssa->def = nir_fdot(&b->nb, src[0], src[1]);
+      dest->def = nir_fdot(&b->nb, src[0], src[1]);
       break;
 
    case SpvOpIAddCarry:
-      vtn_assert(glsl_type_is_struct_or_ifc(val->ssa->type));
-      val->ssa->elems[0]->def = nir_iadd(&b->nb, src[0], src[1]);
-      val->ssa->elems[1]->def = nir_uadd_carry(&b->nb, src[0], src[1]);
+      vtn_assert(glsl_type_is_struct_or_ifc(dest_type));
+      dest->elems[0]->def = nir_iadd(&b->nb, src[0], src[1]);
+      dest->elems[1]->def = nir_uadd_carry(&b->nb, src[0], src[1]);
       break;
 
    case SpvOpISubBorrow:
-      vtn_assert(glsl_type_is_struct_or_ifc(val->ssa->type));
-      val->ssa->elems[0]->def = nir_isub(&b->nb, src[0], src[1]);
-      val->ssa->elems[1]->def = nir_usub_borrow(&b->nb, src[0], src[1]);
+      vtn_assert(glsl_type_is_struct_or_ifc(dest_type));
+      dest->elems[0]->def = nir_isub(&b->nb, src[0], src[1]);
+      dest->elems[1]->def = nir_usub_borrow(&b->nb, src[0], src[1]);
       break;
 
    case SpvOpUMulExtended: {
-      vtn_assert(glsl_type_is_struct_or_ifc(val->ssa->type));
+      vtn_assert(glsl_type_is_struct_or_ifc(dest_type));
       nir_ssa_def *umul = nir_umul_2x32_64(&b->nb, src[0], src[1]);
-      val->ssa->elems[0]->def = nir_unpack_64_2x32_split_x(&b->nb, umul);
-      val->ssa->elems[1]->def = nir_unpack_64_2x32_split_y(&b->nb, umul);
+      dest->elems[0]->def = nir_unpack_64_2x32_split_x(&b->nb, umul);
+      dest->elems[1]->def = nir_unpack_64_2x32_split_y(&b->nb, umul);
       break;
    }
 
    case SpvOpSMulExtended: {
-      vtn_assert(glsl_type_is_struct_or_ifc(val->ssa->type));
+      vtn_assert(glsl_type_is_struct_or_ifc(dest_type));
       nir_ssa_def *smul = nir_imul_2x32_64(&b->nb, src[0], src[1]);
-      val->ssa->elems[0]->def = nir_unpack_64_2x32_split_x(&b->nb, smul);
-      val->ssa->elems[1]->def = nir_unpack_64_2x32_split_y(&b->nb, smul);
+      dest->elems[0]->def = nir_unpack_64_2x32_split_x(&b->nb, smul);
+      dest->elems[1]->def = nir_unpack_64_2x32_split_y(&b->nb, smul);
       break;
    }
 
    case SpvOpFwidth:
-      val->ssa->def = nir_fadd(&b->nb,
+      dest->def = nir_fadd(&b->nb,
                                nir_fabs(&b->nb, nir_fddx(&b->nb, src[0])),
                                nir_fabs(&b->nb, nir_fddy(&b->nb, src[0])));
       break;
    case SpvOpFwidthFine:
-      val->ssa->def = nir_fadd(&b->nb,
+      dest->def = nir_fadd(&b->nb,
                                nir_fabs(&b->nb, nir_fddx_fine(&b->nb, src[0])),
                                nir_fabs(&b->nb, nir_fddy_fine(&b->nb, src[0])));
       break;
    case SpvOpFwidthCoarse:
-      val->ssa->def = nir_fadd(&b->nb,
+      dest->def = nir_fadd(&b->nb,
                                nir_fabs(&b->nb, nir_fddx_coarse(&b->nb, src[0])),
                                nir_fabs(&b->nb, nir_fddy_coarse(&b->nb, src[0])));
       break;
 
    case SpvOpVectorTimesScalar:
       /* The builder will take care of splatting for us. */
-      val->ssa->def = nir_fmul(&b->nb, src[0], src[1]);
+      dest->def = nir_fmul(&b->nb, src[0], src[1]);
       break;
 
    case SpvOpIsNan:
-      val->ssa->def = nir_fne(&b->nb, src[0], src[0]);
+      dest->def = nir_fneu(&b->nb, src[0], src[0]);
+      break;
+
+   case SpvOpOrdered:
+      dest->def = nir_iand(&b->nb, nir_feq(&b->nb, src[0], src[0]),
+                                   nir_feq(&b->nb, src[1], src[1]));
+      break;
+
+   case SpvOpUnordered:
+      dest->def = nir_ior(&b->nb, nir_fneu(&b->nb, src[0], src[0]),
+                                  nir_fneu(&b->nb, src[1], src[1]));
       break;
 
    case SpvOpIsInf: {
       nir_ssa_def *inf = nir_imm_floatN_t(&b->nb, INFINITY, src[0]->bit_size);
-      val->ssa->def = nir_ieq(&b->nb, nir_fabs(&b->nb, src[0]), inf);
+      dest->def = nir_ieq(&b->nb, nir_fabs(&b->nb, src[0]), inf);
       break;
    }
 
@@ -521,7 +539,7 @@ vtn_handle_alu(struct vtn_builder *b, SpvOp opcode,
    case SpvOpFUnordGreaterThanEqual: {
       bool swap;
       unsigned src_bit_size = glsl_get_bit_size(vtn_src[0]->type);
-      unsigned dst_bit_size = glsl_get_bit_size(type);
+      unsigned dst_bit_size = glsl_get_bit_size(dest_type);
       nir_op op = vtn_nir_alu_op_for_spirv_opcode(b, opcode, &swap,
                                                   src_bit_size, dst_bit_size);
 
@@ -531,15 +549,16 @@ vtn_handle_alu(struct vtn_builder *b, SpvOp opcode,
          src[1] = tmp;
       }
 
-      val->ssa->def =
+      dest->def =
          nir_ior(&b->nb,
                  nir_build_alu(&b->nb, op, src[0], src[1], NULL, NULL),
                  nir_ior(&b->nb,
-                         nir_fne(&b->nb, src[0], src[0]),
-                         nir_fne(&b->nb, src[1], src[1])));
+                         nir_fneu(&b->nb, src[0], src[0]),
+                         nir_fneu(&b->nb, src[1], src[1])));
       break;
    }
 
+   case SpvOpLessOrGreater:
    case SpvOpFOrdNotEqual: {
       /* For all the SpvOpFOrd* comparisons apart from NotEqual, the value
        * from the ALU will probably already be false if the operands are not
@@ -547,13 +566,13 @@ vtn_handle_alu(struct vtn_builder *b, SpvOp opcode,
        */
       bool swap;
       unsigned src_bit_size = glsl_get_bit_size(vtn_src[0]->type);
-      unsigned dst_bit_size = glsl_get_bit_size(type);
+      unsigned dst_bit_size = glsl_get_bit_size(dest_type);
       nir_op op = vtn_nir_alu_op_for_spirv_opcode(b, opcode, &swap,
                                                   src_bit_size, dst_bit_size);
 
       assert(!swap);
 
-      val->ssa->def =
+      dest->def =
          nir_iand(&b->nb,
                   nir_build_alu(&b->nb, op, src[0], src[1], NULL, NULL),
                   nir_iand(&b->nb,
@@ -562,43 +581,15 @@ vtn_handle_alu(struct vtn_builder *b, SpvOp opcode,
       break;
    }
 
-   case SpvOpBitcast:
-      /* From the definition of OpBitcast in the SPIR-V 1.2 spec:
-       *
-       *    "If Result Type has the same number of components as Operand, they
-       *    must also have the same component width, and results are computed
-       *    per component.
-       *
-       *    If Result Type has a different number of components than Operand,
-       *    the total number of bits in Result Type must equal the total
-       *    number of bits in Operand. Let L be the type, either Result Type
-       *    or Operand’s type, that has the larger number of components. Let S
-       *    be the other type, with the smaller number of components. The
-       *    number of components in L must be an integer multiple of the
-       *    number of components in S.  The first component (that is, the only
-       *    or lowest-numbered component) of S maps to the first components of
-       *    L, and so on, up to the last component of S mapping to the last
-       *    components of L. Within this mapping, any single component of S
-       *    (mapping to multiple components of L) maps its lower-ordered bits
-       *    to the lower-numbered components of L."
-       */
-      vtn_fail_if(src[0]->num_components * src[0]->bit_size !=
-                  glsl_get_vector_elements(type) * glsl_get_bit_size(type),
-                  "Source and destination of OpBitcast must have the same "
-                  "total number of bits");
-      val->ssa->def = nir_bitcast_vector(&b->nb, src[0],
-                                         glsl_get_bit_size(type));
-      break;
-
    case SpvOpFConvert: {
       nir_alu_type src_alu_type = nir_get_nir_type_for_glsl_type(vtn_src[0]->type);
-      nir_alu_type dst_alu_type = nir_get_nir_type_for_glsl_type(type);
+      nir_alu_type dst_alu_type = nir_get_nir_type_for_glsl_type(dest_type);
       nir_rounding_mode rounding_mode = nir_rounding_mode_undef;
 
-      vtn_foreach_decoration(b, val, handle_rounding_mode, &rounding_mode);
+      vtn_foreach_decoration(b, dest_val, handle_rounding_mode, &rounding_mode);
       nir_op op = nir_type_conversion_op(src_alu_type, dst_alu_type, rounding_mode);
 
-      val->ssa->def = nir_build_alu(&b->nb, op, src[0], src[1], NULL, NULL);
+      dest->def = nir_build_alu(&b->nb, op, src[0], src[1], NULL, NULL);
       break;
    }
 
@@ -610,7 +601,7 @@ vtn_handle_alu(struct vtn_builder *b, SpvOp opcode,
    case SpvOpShiftRightLogical: {
       bool swap;
       unsigned src0_bit_size = glsl_get_bit_size(vtn_src[0]->type);
-      unsigned dst_bit_size = glsl_get_bit_size(type);
+      unsigned dst_bit_size = glsl_get_bit_size(dest_type);
       nir_op op = vtn_nir_alu_op_for_spirv_opcode(b, opcode, &swap,
                                                   src0_bit_size, dst_bit_size);
 
@@ -633,27 +624,33 @@ vtn_handle_alu(struct vtn_builder *b, SpvOp opcode,
             src[i] = nir_u2u32(&b->nb, src[i]);
          }
       }
-      val->ssa->def = nir_build_alu(&b->nb, op, src[0], src[1], src[2], src[3]);
+      dest->def = nir_build_alu(&b->nb, op, src[0], src[1], src[2], src[3]);
       break;
    }
 
-   case SpvOpSignBitSet: {
-      unsigned src_bit_size = glsl_get_bit_size(vtn_src[0]->type);
-      if (src[0]->num_components == 1)
-         val->ssa->def =
-            nir_ushr(&b->nb, src[0], nir_imm_int(&b->nb, src_bit_size - 1));
-      else
-         val->ssa->def =
-            nir_ishr(&b->nb, src[0], nir_imm_int(&b->nb, src_bit_size - 1));
+   case SpvOpSignBitSet:
+      dest->def = nir_i2b(&b->nb,
+         nir_ushr(&b->nb, src[0], nir_imm_int(&b->nb, src[0]->bit_size - 1)));
+      break;
 
-      val->ssa->def = nir_i2b(&b->nb, val->ssa->def);
+   case SpvOpUCountTrailingZerosINTEL:
+      dest->def = nir_umin(&b->nb,
+                               nir_find_lsb(&b->nb, src[0]),
+                               nir_imm_int(&b->nb, 32u));
+      break;
+
+   case SpvOpBitCount: {
+      /* bit_count always returns int32, but the SPIR-V opcode just says the return
+       * value needs to be big enough to store the number of bits.
+       */
+      dest->def = nir_u2u(&b->nb, nir_bit_count(&b->nb, src[0]), glsl_get_bit_size(dest_type));
       break;
    }
 
    default: {
       bool swap;
       unsigned src_bit_size = glsl_get_bit_size(vtn_src[0]->type);
-      unsigned dst_bit_size = glsl_get_bit_size(type);
+      unsigned dst_bit_size = glsl_get_bit_size(dest_type);
       nir_op op = vtn_nir_alu_op_for_spirv_opcode(b, opcode, &swap,
                                                   src_bit_size, dst_bit_size);
 
@@ -674,10 +671,62 @@ vtn_handle_alu(struct vtn_builder *b, SpvOp opcode,
          break;
       }
 
-      val->ssa->def = nir_build_alu(&b->nb, op, src[0], src[1], src[2], src[3]);
+      dest->def = nir_build_alu(&b->nb, op, src[0], src[1], src[2], src[3]);
       break;
    } /* default */
    }
 
+   switch (opcode) {
+   case SpvOpIAdd:
+   case SpvOpIMul:
+   case SpvOpISub:
+   case SpvOpShiftLeftLogical:
+   case SpvOpSNegate: {
+      nir_alu_instr *alu = nir_instr_as_alu(dest->def->parent_instr);
+      vtn_foreach_decoration(b, dest_val, handle_no_wrap, alu);
+      break;
+   }
+   default:
+      /* Do nothing. */
+      break;
+   }
+
+   vtn_push_ssa_value(b, w[2], dest);
+
    b->nb.exact = b->exact;
 }
+
+void
+vtn_handle_bitcast(struct vtn_builder *b, const uint32_t *w, unsigned count)
+{
+   vtn_assert(count == 4);
+   /* From the definition of OpBitcast in the SPIR-V 1.2 spec:
+    *
+    *    "If Result Type has the same number of components as Operand, they
+    *    must also have the same component width, and results are computed per
+    *    component.
+    *
+    *    If Result Type has a different number of components than Operand, the
+    *    total number of bits in Result Type must equal the total number of
+    *    bits in Operand. Let L be the type, either Result Type or Operand’s
+    *    type, that has the larger number of components. Let S be the other
+    *    type, with the smaller number of components. The number of components
+    *    in L must be an integer multiple of the number of components in S.
+    *    The first component (that is, the only or lowest-numbered component)
+    *    of S maps to the first components of L, and so on, up to the last
+    *    component of S mapping to the last components of L. Within this
+    *    mapping, any single component of S (mapping to multiple components of
+    *    L) maps its lower-ordered bits to the lower-numbered components of L."
+    */
+
+   struct vtn_type *type = vtn_get_type(b, w[1]);
+   struct nir_ssa_def *src = vtn_get_nir_ssa(b, w[3]);
+
+   vtn_fail_if(src->num_components * src->bit_size !=
+               glsl_get_vector_elements(type->type) * glsl_get_bit_size(type->type),
+               "Source and destination of OpBitcast must have the same "
+               "total number of bits");
+   nir_ssa_def *val =
+      nir_bitcast_vector(&b->nb, src, glsl_get_bit_size(type->type));
+   vtn_push_nir_ssa(b, w[2], val);
+}