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i965/fs: Do more register coalescing by using the interference graph.

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By using the live variables code for determining interference, we can
handle coalescing in the presence of control flow, which the other
register coalescing path couldn't.

Total instructions: 207184 -> 206990
74/1246 programs affected (5.9%)
33993 -> 33799 instructions in affected programs (0.6% reduction)

There is a newerth shader that loses out, because of some extra MOVs
that now get their dead-code nature obscured by coalescing.  This
should be fixed by doing better at dead code elimination.
This commit is contained in:
Eric Anholt 2012-05-08 10:18:20 -07:00
parent 1befacc764
commit f220f73b9c
2 changed files with 62 additions and 0 deletions
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61
src/mesa/drivers/dri/i965/brw_fs.cpp
View file

@ -1218,6 +1218,66 @@ fs_visitor::dead_code_eliminate()
return progress;
}
/**
* Implements a second type of register coalescing: This one checks if
* the two regs involved in a raw move don't interfere, in which case
* they can both by stored in the same place and the MOV removed.
*/
bool
fs_visitor::register_coalesce_2()
{
bool progress = false;
calculate_live_intervals();
foreach_list_safe(node, &this->instructions) {
fs_inst *inst = (fs_inst *)node;
if (inst->opcode != BRW_OPCODE_MOV ||
inst->predicated ||
inst->saturate ||
inst->src[0].file != GRF ||
inst->src[0].negate ||
inst->src[0].abs ||
inst->src[0].smear != -1 ||
inst->dst.file != GRF ||
inst->dst.type != inst->src[0].type ||
virtual_grf_sizes[inst->src[0].reg] != 1 ||
virtual_grf_interferes(inst->dst.reg, inst->src[0].reg)) {
continue;
}
int reg_from = inst->src[0].reg;
assert(inst->src[0].reg_offset == 0);
int reg_to = inst->dst.reg;
int reg_to_offset = inst->dst.reg_offset;
foreach_list_safe(node, &this->instructions) {
fs_inst *scan_inst = (fs_inst *)node;
if (scan_inst->dst.file == GRF &&
scan_inst->dst.reg == reg_from) {
scan_inst->dst.reg = reg_to;
scan_inst->dst.reg_offset = reg_to_offset;
}
for (int i = 0; i < 3; i++) {
if (scan_inst->src[i].file == GRF &&
scan_inst->src[i].reg == reg_from) {
scan_inst->src[i].reg = reg_to;
scan_inst->src[i].reg_offset = reg_to_offset;
}
}
}
inst->remove();
live_intervals_valid = false;
progress = true;
continue;
}
return progress;
}
bool
fs_visitor::register_coalesce()
{
@ -1684,6 +1744,7 @@ fs_visitor::run()
progress = opt_cse() || progress;
progress = opt_copy_propagate() || progress;
progress = register_coalesce() || progress;
progress = register_coalesce_2() || progress;
progress = compute_to_mrf() || progress;
progress = dead_code_eliminate() || progress;
} while (progress);

1
src/mesa/drivers/dri/i965/brw_fs.h
View file

@ -495,6 +495,7 @@ public:
bool opt_copy_propagate_local(void *mem_ctx, fs_bblock *block,
exec_list *acp);
bool register_coalesce();
bool register_coalesce_2();
bool compute_to_mrf();
bool dead_code_eliminate();
bool remove_dead_constants();