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i965/cfg: Eliminate an empty then-branch of an if/else/endif

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On BDW,

total instructions in shared programs: 8448571 -> 8448367 (-0.00%)
instructions in affected programs: 21000 -> 20796 (-0.97%)
helped: 116
HURT: 0

v2: Remove spurious attempt to combine the if_block with the (removed!)
else_block.  Suggested by Matt and Curro.  Correct the comment
describing what the new pass does.  Suggested by Matt.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Francisco Jerez <currojerez@riseup.net>
This commit is contained in:
Ian Romanick 2016-02-24 19:11:39 -08:00
parent c7deee69ea
commit 69bb063ec2
1 changed files with 14 additions and 0 deletions
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14
src/mesa/drivers/dri/i965/brw_dead_control_flow.cpp
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@ -34,6 +34,7 @@
* - if/endif
* . else in else/endif
* - if/else/endif
* - else in if/else
*/
bool
dead_control_flow_eliminate(backend_shader *s)
@ -114,6 +115,19 @@ dead_control_flow_eliminate(backend_shader *s)
progress = true;
}
} else if (inst->opcode == BRW_OPCODE_ELSE &&
prev_inst->opcode == BRW_OPCODE_IF) {
bblock_t *const else_block = block;
backend_instruction *const if_inst = prev_inst;
backend_instruction *const else_inst = inst;
/* Since the else-branch is becoming the new then-branch, the
* condition has to be inverted.
*/
if_inst->predicate_inverse = !if_inst->predicate_inverse;
else_inst->remove(else_block);
progress = true;
}
}