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i965/fs: Always invert predicate of SEL with swapped arguments 

Commit b616164 added an optimization of b2f generation of a comparison.
It also included an extra optimization of one of the comparison values
is a constant of zero.  The trick was that some value was known to be
zero, so that value could be used in the SEL instruction instead of
potentially loading 0.0 into a register.

This change switched the order of the arguments to the SEL, and, for
some unknown reason, I thought that the predicate should therefore
only be inverted for the == case.  Clearly, it should always be
inverted.

Fixes piglit fs-notEqual-of-expression.shader_test and
fs-equal-of-expression.shader_test.

v2: Don't do the "register already has zero" optimization for the '== 0'
case.  In that case, the register does not have zero when we want to
produce a zero result.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=89722
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org> [v1]
Tested-by: Lu Hua <huax.lu@intel.com>
This commit is contained in:
Ian Romanick 2015-03-23 12:03:56 -07:00
parent e0994e0f97
commit 05a1d84491
1 changed files with 5 additions and 5 deletions
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10
src/mesa/drivers/dri/i965/brw_fs_visitor.cpp
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@ -502,15 +502,15 @@ fs_visitor::try_emit_b2f_of_comparison(ir_expression *ir)
* and(16) g4<1>D g2<8,8,1>D 1D
* and(16) m6<1>D -g4<8,8,1>D 0x3f800000UD
*
* When the comparison is either == 0.0 or != 0.0 using the knowledge that
* the true (or false) case already results in zero would allow better code
* generation by possibly avoiding a load-immediate instruction.
* When the comparison is != 0.0 using the knowledge that the false case
* already results in zero would allow better code generation by possibly
* avoiding a load-immediate instruction.
*/
ir_expression *cmp = ir->operands[0]->as_expression();
if (cmp == NULL)
return false;
if (cmp->operation == ir_binop_equal || cmp->operation == ir_binop_nequal) {
if (cmp->operation == ir_binop_nequal) {
for (unsigned i = 0; i < 2; i++) {
ir_constant *c = cmp->operands[i]->as_constant();
if (c == NULL || !c->is_zero())
@ -538,7 +538,7 @@ fs_visitor::try_emit_b2f_of_comparison(ir_expression *ir)
fs_inst *inst = emit(SEL(this->result, op[i ^ 1], fs_reg(1.0f)));
inst->predicate = BRW_PREDICATE_NORMAL;
inst->predicate_inverse = cmp->operation == ir_binop_equal;
inst->predicate_inverse = true;
return true;
}
}