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glsl: Implement usubBorrow() built-in for ARB_gpu_shader5.

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i965 implements this with a single (multiple destination) instruction,
SUBB. Emitting SUBB directly from usubBorrow() would be ideal, but our
optimization passes don't know how to copy with expressions with
side-effects.

Radeon has an SUBB_UINT instruction that only generates the borrow
bit. I've chosen to go this route and implement usubBorrow() by doing the
subtraction and the borrow operations separately.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
This commit is contained in:
Matt Turner 2013-09-17 18:02:05 -07:00
parent 6c125973f3
commit 6f9428eb68
1 changed files with 21 additions and 0 deletions
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21
src/glsl/builtin_functions.cpp
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@ -532,6 +532,7 @@ private:
B2(ldexp)
B2(frexp)
B1(uaddCarry)
B1(usubBorrow)
#undef B0
#undef B1
#undef B2
@ -1954,6 +1955,12 @@ builtin_builder::create_builtins()
_uaddCarry(glsl_type::uvec3_type),
_uaddCarry(glsl_type::uvec4_type),
NULL);
add_function("usubBorrow",
_usubBorrow(glsl_type::uint_type),
_usubBorrow(glsl_type::uvec2_type),
_usubBorrow(glsl_type::uvec3_type),
_usubBorrow(glsl_type::uvec4_type),
NULL);
#undef F
#undef FI
#undef FIU
@ -3741,6 +3748,20 @@ builtin_builder::_uaddCarry(const glsl_type *type)
return sig;
}
ir_function_signature *
builtin_builder::_usubBorrow(const glsl_type *type)
{
ir_variable *x = in_var(type, "x");
ir_variable *y = in_var(type, "y");
ir_variable *borrow = out_var(type, "borrow");
MAKE_SIG(type, gpu_shader5, 3, x, y, borrow);
body.emit(assign(borrow, ir_builder::borrow(x, y)));
body.emit(ret(sub(x, y)));
return sig;
}
/** @} */
/******************************************************************************/