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glsl: Add lowering pass for ir_unop_bitfield_reverse

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Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>
This commit is contained in:
Ian Romanick
2016-06-24 00:11:26 -07:00
parent 3079dcb00c
commit ad9acb19c3
2 changed files with 92 additions and 0 deletions
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91
src/compiler/glsl/lower_instructions.cpp
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@@ -162,6 +162,7 @@ private:
void bit_count_to_math(ir_expression *);
void extract_to_shifts(ir_expression *);
void insert_to_shifts(ir_expression *);
void reverse_to_shifts(ir_expression *ir);
};
} /* anonymous namespace */
@@ -1143,6 +1144,92 @@ lower_instructions_visitor::insert_to_shifts(ir_expression *ir)
this->progress = true;
}
void
lower_instructions_visitor::reverse_to_shifts(ir_expression *ir)
{
/* For more details, see:
*
* http://graphics.stanford.edu/~seander/bithacks.html#ReverseParallel
*/
ir_constant *c1 =
new(ir) ir_constant(1u, ir->operands[0]->type->vector_elements);
ir_constant *c2 =
new(ir) ir_constant(2u, ir->operands[0]->type->vector_elements);
ir_constant *c4 =
new(ir) ir_constant(4u, ir->operands[0]->type->vector_elements);
ir_constant *c8 =
new(ir) ir_constant(8u, ir->operands[0]->type->vector_elements);
ir_constant *c16 =
new(ir) ir_constant(16u, ir->operands[0]->type->vector_elements);
ir_constant *c33333333 =
new(ir) ir_constant(0x33333333u, ir->operands[0]->type->vector_elements);
ir_constant *c55555555 =
new(ir) ir_constant(0x55555555u, ir->operands[0]->type->vector_elements);
ir_constant *c0F0F0F0F =
new(ir) ir_constant(0x0F0F0F0Fu, ir->operands[0]->type->vector_elements);
ir_constant *c00FF00FF =
new(ir) ir_constant(0x00FF00FFu, ir->operands[0]->type->vector_elements);
ir_variable *temp =
new(ir) ir_variable(glsl_type::uvec(ir->operands[0]->type->vector_elements),
"temp", ir_var_temporary);
ir_instruction &i = *base_ir;
i.insert_before(temp);
if (ir->operands[0]->type->base_type == GLSL_TYPE_UINT) {
i.insert_before(assign(temp, ir->operands[0]));
} else {
assert(ir->operands[0]->type->base_type == GLSL_TYPE_INT);
i.insert_before(assign(temp, i2u(ir->operands[0])));
}
/* Swap odd and even bits.
*
* temp = ((temp >> 1) & 0x55555555u) | ((temp & 0x55555555u) << 1);
*/
i.insert_before(assign(temp, bit_or(bit_and(rshift(temp, c1), c55555555),
lshift(bit_and(temp, c55555555->clone(ir, NULL)),
c1->clone(ir, NULL)))));
/* Swap consecutive pairs.
*
* temp = ((temp >> 2) & 0x33333333u) | ((temp & 0x33333333u) << 2);
*/
i.insert_before(assign(temp, bit_or(bit_and(rshift(temp, c2), c33333333),
lshift(bit_and(temp, c33333333->clone(ir, NULL)),
c2->clone(ir, NULL)))));
/* Swap nibbles.
*
* temp = ((temp >> 4) & 0x0F0F0F0Fu) | ((temp & 0x0F0F0F0Fu) << 4);
*/
i.insert_before(assign(temp, bit_or(bit_and(rshift(temp, c4), c0F0F0F0F),
lshift(bit_and(temp, c0F0F0F0F->clone(ir, NULL)),
c4->clone(ir, NULL)))));
/* The last step is, basically, bswap. Swap the bytes, then swap the
* words. When this code is run through GCC on x86, it does generate a
* bswap instruction.
*
* temp = ((temp >> 8) & 0x00FF00FFu) | ((temp & 0x00FF00FFu) << 8);
* temp = ( temp >> 16 ) | ( temp << 16);
*/
i.insert_before(assign(temp, bit_or(bit_and(rshift(temp, c8), c00FF00FF),
lshift(bit_and(temp, c00FF00FF->clone(ir, NULL)),
c8->clone(ir, NULL)))));
if (ir->operands[0]->type->base_type == GLSL_TYPE_UINT) {
ir->operation = ir_binop_bit_or;
ir->operands[0] = rshift(temp, c16);
ir->operands[1] = lshift(temp, c16->clone(ir, NULL));
} else {
ir->operation = ir_unop_u2i;
ir->operands[0] = bit_or(rshift(temp, c16),
lshift(temp, c16->clone(ir, NULL)));
}
this->progress = true;
}
ir_visitor_status
lower_instructions_visitor::visit_leave(ir_expression *ir)
{
@@ -1260,6 +1347,10 @@ lower_instructions_visitor::visit_leave(ir_expression *ir)
insert_to_shifts(ir);
break;
case ir_unop_bitfield_reverse:
if (lowering(REVERSE_TO_SHIFTS))
reverse_to_shifts(ir);
break;
default:
return visit_continue;