ir_to_mesa: Emit a MAD(b, -a, b) for !a && b
!a && b occurs frequently when nexted if-statements have been flattened. It should also be possible use a MAD for (a && b) || c, though that would require a MAD_SAT. Reviewed-by: Eric Anholt <eric@anholt.net>
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@ -314,6 +314,8 @@ public:
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GLboolean try_emit_mad(ir_expression *ir,
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int mul_operand);
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bool try_emit_mad_for_and_not(ir_expression *ir,
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int mul_operand);
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GLboolean try_emit_sat(ir_expression *ir);
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void emit_swz(ir_expression *ir);
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@ -892,6 +894,46 @@ ir_to_mesa_visitor::try_emit_mad(ir_expression *ir, int mul_operand)
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return true;
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}
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/**
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* Emit OPCODE_MAD(a, -b, a) instead of AND(a, NOT(b))
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*
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* The logic values are 1.0 for true and 0.0 for false. Logical-and is
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* implemented using multiplication, and logical-or is implemented using
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* addition. Logical-not can be implemented as (true - x), or (1.0 - x).
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* As result, the logical expression (a & !b) can be rewritten as:
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*
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* - a * !b
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* - a * (1 - b)
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* - (a * 1) - (a * b)
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* - a + -(a * b)
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* - a + (a * -b)
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*
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* This final expression can be implemented as a single MAD(a, -b, a)
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* instruction.
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*/
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bool
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ir_to_mesa_visitor::try_emit_mad_for_and_not(ir_expression *ir, int try_operand)
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{
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const int other_operand = 1 - try_operand;
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src_reg a, b;
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ir_expression *expr = ir->operands[try_operand]->as_expression();
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if (!expr || expr->operation != ir_unop_logic_not)
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return false;
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ir->operands[other_operand]->accept(this);
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a = this->result;
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expr->operands[0]->accept(this);
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b = this->result;
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b.negate = ~b.negate;
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this->result = get_temp(ir->type);
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emit(ir, OPCODE_MAD, dst_reg(this->result), a, b, a);
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return true;
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}
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GLboolean
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ir_to_mesa_visitor::try_emit_sat(ir_expression *ir)
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{
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@ -1088,6 +1130,16 @@ ir_to_mesa_visitor::visit(ir_expression *ir)
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if (try_emit_mad(ir, 0))
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return;
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}
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/* Quick peephole: Emit OPCODE_MAD(-a, -b, a) instead of AND(a, NOT(b))
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*/
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if (ir->operation == ir_binop_logic_and) {
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if (try_emit_mad_for_and_not(ir, 1))
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return;
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if (try_emit_mad_for_and_not(ir, 0))
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return;
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}
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if (try_emit_sat(ir))
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return;
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