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i965/vec4: Handle ir_triop_lrp on Gen4-5 as well.

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When the vec4 backend encountered an ir_triop_lrp, it always emitted an
actual LRP instruction, which only exists on Gen6+.  Gen4-5 used
lower_instructions() to decompose ir_triop_lrp at the IR level.

Since commit 8d37e9915a ("glsl: Optimize open-coded lrp into lrp."),
we've had an bug where lower_instructions translates ir_triop_lrp into
arithmetic, but opt_algebraic reassembles it back into a lrp.

To avoid this ordering concern, just handle ir_triop_lrp in the backend.
The FS backend already does this, so we may as well do likewise.

v2: Add a comment reminding us that we could emit better assembly if we
    implemented the infrastructure necessary to support using MAC.
    (Assembly code provided by Eric Anholt).

Cc: "10.1" <mesa-stable@lists.freedesktop.org>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=75253
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Acked-by: Eric Anholt <eric@anholt.net>
(cherry picked from commit 56879a7ac4)
This commit is contained in:
Kenneth Graunke 2014-02-23 16:29:46 -08:00 • committed by Ian Romanick
parent 2475db34a0
commit 24abd48ac0
2 changed files with 38 additions and 7 deletions
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3
src/mesa/drivers/dri/i965/brw_vec4.h
View file

@ -472,6 +472,9 @@ public:
void emit_minmax(uint32_t condmod, dst_reg dst, src_reg src0, src_reg src1);
void emit_lrp(const dst_reg &dst,
const src_reg &x, const src_reg &y, const src_reg &a);
void emit_block_move(dst_reg *dst, src_reg *src,
const struct glsl_type *type, uint32_t predicate);

42
src/mesa/drivers/dri/i965/brw_vec4_visitor.cpp
View file

@ -1140,6 +1140,40 @@ vec4_visitor::emit_minmax(uint32_t conditionalmod, dst_reg dst,
}
}
void
vec4_visitor::emit_lrp(const dst_reg &dst,
const src_reg &x, const src_reg &y, const src_reg &a)
{
if (brw->gen >= 6) {
/* Note that the instruction's argument order is reversed from GLSL
* and the IR.
*/
emit(LRP(dst,
fix_3src_operand(a), fix_3src_operand(y), fix_3src_operand(x)));
} else {
/* Earlier generations don't support three source operations, so we
* need to emit x*(1-a) + y*a.
*
* A better way to do this would be:
* ADD one_minus_a, negate(a), 1.0f
* MUL null, y, a
* MAC dst, x, one_minus_a
* but we would need to support MAC and implicit accumulator.
*/
dst_reg y_times_a = dst_reg(this, glsl_type::vec4_type);
dst_reg one_minus_a = dst_reg(this, glsl_type::vec4_type);
dst_reg x_times_one_minus_a = dst_reg(this, glsl_type::vec4_type);
y_times_a.writemask = dst.writemask;
one_minus_a.writemask = dst.writemask;
x_times_one_minus_a.writemask = dst.writemask;
emit(MUL(y_times_a, y, a));
emit(ADD(one_minus_a, negate(a), src_reg(1.0f)));
emit(MUL(x_times_one_minus_a, x, src_reg(one_minus_a)));
emit(ADD(dst, src_reg(x_times_one_minus_a), src_reg(y_times_a)));
}
}
static bool
is_16bit_constant(ir_rvalue *rvalue)
{
@ -1623,13 +1657,7 @@ vec4_visitor::visit(ir_expression *ir)
break;
case ir_triop_lrp:
op[0] = fix_3src_operand(op[0]);
op[1] = fix_3src_operand(op[1]);
op[2] = fix_3src_operand(op[2]);
/* Note that the instruction's argument order is reversed from GLSL
* and the IR.
*/
emit(LRP(result_dst, op[2], op[1], op[0]));
emit_lrp(result_dst, op[0], op[1], op[2]);
break;
case ir_triop_csel: