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glsl/lower_instruction: handle denorms and overflow in ldexp correctly 

GLSL ES requires both, and while GLSL explicitly doesn't require correct
overflow handling, it does appear to require handling input inf/denorms
correctly.

Fixes dEQP-GLES31.functional.shaders.builtin_functions.precision.ldexp.*

Cc: mesa-stable@lists.freedesktop.org
Acked-by: Matt Turner <mattst88@gmail.com>
Acked-by: Marek Olšák <marek.olsak@amd.com>
Tested-by: Dieter Nützel <Dieter@nuetzel-hh.de>
This commit is contained in:
Nicolai Hähnle 2017-09-15 16:39:31 +02:00
parent a208cd7ae4
commit 93bf9c114b
1 changed files with 106 additions and 63 deletions
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169
src/compiler/glsl/lower_instructions.cpp
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@ -365,13 +365,21 @@ lower_instructions_visitor::ldexp_to_arith(ir_expression *ir)
* into
*
* extracted_biased_exp = rshift(bitcast_f2i(abs(x)), exp_shift);
* resulting_biased_exp = extracted_biased_exp + exp;
* resulting_biased_exp = min(extracted_biased_exp + exp, 255);
*
* if (resulting_biased_exp < 1 || x == 0.0f) {
* return copysign(0.0, x);
* if (extracted_biased_exp >= 255)
* return x; // +/-inf, NaN
*
* sign_mantissa = bitcast_f2u(x) & sign_mantissa_mask;
*
* if (min(resulting_biased_exp, extracted_biased_exp) < 1)
* resulting_biased_exp = 0;
* if (resulting_biased_exp >= 255 ||
* min(resulting_biased_exp, extracted_biased_exp) < 1) {
* sign_mantissa &= sign_mask;
* }
*
* return bitcast_u2f((bitcast_f2u(x) & sign_mantissa_mask) |
* return bitcast_u2f(sign_mantissa |
* lshift(i2u(resulting_biased_exp), exp_shift));
*
* which we can't actually implement as such, since the GLSL IR doesn't
@ -379,45 +387,58 @@ lower_instructions_visitor::ldexp_to_arith(ir_expression *ir)
* using conditional-select:
*
* extracted_biased_exp = rshift(bitcast_f2i(abs(x)), exp_shift);
* resulting_biased_exp = extracted_biased_exp + exp;
* resulting_biased_exp = min(extracted_biased_exp + exp, 255);
*
* is_not_zero_or_underflow = logic_and(nequal(x, 0.0f),
* gequal(resulting_biased_exp, 1);
* x = csel(is_not_zero_or_underflow, x, copysign(0.0f, x));
* resulting_biased_exp = csel(is_not_zero_or_underflow,
* resulting_biased_exp, 0);
* sign_mantissa = bitcast_f2u(x) & sign_mantissa_mask;
*
* return bitcast_u2f((bitcast_f2u(x) & sign_mantissa_mask) |
* lshift(i2u(resulting_biased_exp), exp_shift));
* flush_to_zero = lequal(min(resulting_biased_exp, extracted_biased_exp), 0);
* resulting_biased_exp = csel(flush_to_zero, 0, resulting_biased_exp)
* zero_mantissa = logic_or(flush_to_zero,
* gequal(resulting_biased_exp, 255));
* sign_mantissa = csel(zero_mantissa, sign_mantissa & sign_mask, sign_mantissa);
*
* result = sign_mantissa |
* lshift(i2u(resulting_biased_exp), exp_shift));
*
* return csel(extracted_biased_exp >= 255, x, bitcast_u2f(result));
*
* The definition of ldexp in the GLSL spec says:
*
* "If this product is too large to be represented in the
* floating-point type, the result is undefined."
*
* However, the definition of ldexp in the GLSL ES spec does not contain
* this sentence, so we do need to handle overflow correctly.
*
* There is additional language limiting the defined range of exp, but this
* is merely to allow implementations that store 2^exp in a temporary
* variable.
*/
const unsigned vec_elem = ir->type->vector_elements;
/* Types */
const glsl_type *ivec = glsl_type::get_instance(GLSL_TYPE_INT, vec_elem, 1);
const glsl_type *uvec = glsl_type::get_instance(GLSL_TYPE_UINT, vec_elem, 1);
const glsl_type *bvec = glsl_type::get_instance(GLSL_TYPE_BOOL, vec_elem, 1);
/* Constants */
ir_constant *zeroi = ir_constant::zero(ir, ivec);
ir_constant *sign_mask = new(ir) ir_constant(0x80000000u, vec_elem);
ir_constant *exp_shift = new(ir) ir_constant(23, vec_elem);
/* Temporary variables */
ir_variable *x = new(ir) ir_variable(ir->type, "x", ir_var_temporary);
ir_variable *exp = new(ir) ir_variable(ivec, "exp", ir_var_temporary);
ir_variable *zero_sign_x = new(ir) ir_variable(ir->type, "zero_sign_x",
ir_var_temporary);
ir_variable *result = new(ir) ir_variable(uvec, "result", ir_var_temporary);
ir_variable *extracted_biased_exp =
new(ir) ir_variable(ivec, "extracted_biased_exp", ir_var_temporary);
ir_variable *resulting_biased_exp =
new(ir) ir_variable(ivec, "resulting_biased_exp", ir_var_temporary);
ir_variable *is_not_zero_or_underflow =
new(ir) ir_variable(bvec, "is_not_zero_or_underflow", ir_var_temporary);
ir_variable *sign_mantissa =
new(ir) ir_variable(uvec, "sign_mantissa", ir_var_temporary);
ir_variable *flush_to_zero =
new(ir) ir_variable(bvec, "flush_to_zero", ir_var_temporary);
ir_variable *zero_mantissa =
new(ir) ir_variable(bvec, "zero_mantissa", ir_var_temporary);
ir_instruction &i = *base_ir;
@ -430,61 +451,83 @@ lower_instructions_visitor::ldexp_to_arith(ir_expression *ir)
/* Extract the biased exponent from <x>. */
i.insert_before(extracted_biased_exp);
i.insert_before(assign(extracted_biased_exp,
rshift(bitcast_f2i(abs(x)), exp_shift)));
rshift(bitcast_f2i(abs(x)),
new(ir) ir_constant(23, vec_elem))));
/* The definition of ldexp in the GLSL 4.60 spec says:
*
* "If exp is greater than +128 (single-precision) or +1024
* (double-precision), the value returned is undefined. If exp is less
* than -126 (single-precision) or -1022 (double-precision), the value
* returned may be flushed to zero."
*
* So we do not have to guard against the possibility of addition overflow,
* which could happen when exp is close to INT_MAX. Addition underflow
* cannot happen (the worst case is 0 + (-INT_MAX)).
*/
i.insert_before(resulting_biased_exp);
i.insert_before(assign(resulting_biased_exp,
add(extracted_biased_exp, exp)));
min2(add(extracted_biased_exp, exp),
new(ir) ir_constant(255, vec_elem))));
/* Test if result is ±0.0, subnormal, or underflow by checking if the
* resulting biased exponent would be less than 0x1. If so, the result is
* 0.0 with the sign of x. (Actually, invert the conditions so that
* immediate values are the second arguments, which is better for i965)
*/
i.insert_before(zero_sign_x);
i.insert_before(assign(zero_sign_x,
bitcast_u2f(bit_and(bitcast_f2u(x), sign_mask))));
i.insert_before(sign_mantissa);
i.insert_before(assign(sign_mantissa,
bit_and(bitcast_f2u(x),
new(ir) ir_constant(0x807fffffu, vec_elem))));
i.insert_before(is_not_zero_or_underflow);
i.insert_before(assign(is_not_zero_or_underflow,
logic_and(nequal(x, new(ir) ir_constant(0.0f, vec_elem)),
gequal(resulting_biased_exp,
new(ir) ir_constant(0x1, vec_elem)))));
i.insert_before(assign(x, csel(is_not_zero_or_underflow,
x, zero_sign_x)));
i.insert_before(assign(resulting_biased_exp,
csel(is_not_zero_or_underflow,
resulting_biased_exp, zeroi)));
/* We could test for overflows by checking if the resulting biased exponent
* would be greater than 0xFE. Turns out we don't need to because the GLSL
* spec says:
/* We flush to zero if the original or resulting biased exponent is 0,
* indicating a +/-0.0 or subnormal input or output.
*
* "If this product is too large to be represented in the
* floating-point type, the result is undefined."
* The mantissa is set to 0 if the resulting biased exponent is 255, since
* an overflow should produce a +/-inf result.
*
* Note that NaN inputs are handled separately.
*/
i.insert_before(flush_to_zero);
i.insert_before(assign(flush_to_zero,
lequal(min2(resulting_biased_exp,
extracted_biased_exp),
ir_constant::zero(ir, ivec))));
i.insert_before(assign(resulting_biased_exp,
csel(flush_to_zero,
ir_constant::zero(ir, ivec),
resulting_biased_exp)));
ir_constant *exp_shift_clone = exp_shift->clone(ir, NULL);
i.insert_before(zero_mantissa);
i.insert_before(assign(zero_mantissa,
logic_or(flush_to_zero,
equal(resulting_biased_exp,
new(ir) ir_constant(255, vec_elem)))));
i.insert_before(assign(sign_mantissa,
csel(zero_mantissa,
bit_and(sign_mantissa,
new(ir) ir_constant(0x80000000u, vec_elem)),
sign_mantissa)));
/* Don't generate new IR that would need to be lowered in an additional
* pass.
*/
i.insert_before(result);
if (!lowering(INSERT_TO_SHIFTS)) {
ir_constant *exp_width = new(ir) ir_constant(8, vec_elem);
ir->operation = ir_unop_bitcast_i2f;
ir->init_num_operands();
ir->operands[0] = bitfield_insert(bitcast_f2i(x), resulting_biased_exp,
exp_shift_clone, exp_width);
ir->operands[1] = NULL;
i.insert_before(assign(result,
bitfield_insert(sign_mantissa,
i2u(resulting_biased_exp),
new(ir) ir_constant(23u, vec_elem),
new(ir) ir_constant(8u, vec_elem))));
} else {
ir_constant *sign_mantissa_mask = new(ir) ir_constant(0x807fffffu, vec_elem);
ir->operation = ir_unop_bitcast_u2f;
ir->init_num_operands();
ir->operands[0] = bit_or(bit_and(bitcast_f2u(x), sign_mantissa_mask),
lshift(i2u(resulting_biased_exp), exp_shift_clone));
ir->operands[1] = NULL;
i.insert_before(assign(result,
bit_or(sign_mantissa,
lshift(i2u(resulting_biased_exp),
new(ir) ir_constant(23, vec_elem)))));
}
ir->operation = ir_triop_csel;
ir->init_num_operands();
ir->operands[0] = gequal(extracted_biased_exp,
new(ir) ir_constant(255, vec_elem));
ir->operands[1] = new(ir) ir_dereference_variable(x);
ir->operands[2] = bitcast_u2f(result);
this->progress = true;
}