From 93bf9c114b7c54e4faf342810bd848527b7d0a80 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Nicolai=20H=C3=A4hnle?= Date: Fri, 15 Sep 2017 16:39:31 +0200 Subject: [PATCH] glsl/lower_instruction: handle denorms and overflow in ldexp correctly MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Acked-by: Marek Olšák Tested-by: Dieter Nützel --- src/compiler/glsl/lower_instructions.cpp | 169 ++++++++++++++--------- 1 file changed, 106 insertions(+), 63 deletions(-) diff --git a/src/compiler/glsl/lower_instructions.cpp b/src/compiler/glsl/lower_instructions.cpp index 0c1408911d2..362562a4af6 100644 --- a/src/compiler/glsl/lower_instructions.cpp +++ b/src/compiler/glsl/lower_instructions.cpp @@ -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 . */ 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; }