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i965/fs: Simplify and improve accuracy of compute_to_mrf() by using regions_overlap().

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Compute-to-mrf was being rather heavy-handed about checking whether
instruction source or destination regions interfere with the copy
instruction, which could conceivably lead to program miscompilation.
Fix it by using regions_overlap() instead of the open-coded and
dubiously correct overlap checks.

Cc: "12.0" <mesa-stable@lists.freedesktop.org>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
(cherry picked from commit bb61e24787)
This commit is contained in:
Francisco Jerez 2016-05-27 12:50:28 -07:00 • committed by Emil Velikov
parent 2d83aad693
commit a6011c6fc6
1 changed files with 13 additions and 47 deletions
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60
src/mesa/drivers/dri/i965/brw_fs.cpp
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@ -2792,19 +2792,6 @@ fs_visitor::compute_to_mrf()
inst->src[0].subreg_offset)
continue;
/* Work out which hardware MRF registers are written by this
* instruction.
*/
int mrf_low = inst->dst.nr & ~BRW_MRF_COMPR4;
int mrf_high;
if (inst->dst.nr & BRW_MRF_COMPR4) {
mrf_high = mrf_low + 4;
} else if (inst->exec_size == 16) {
mrf_high = mrf_low + 1;
} else {
mrf_high = mrf_low;
}
/* Can't compute-to-MRF this GRF if someone else was going to
* read it later.
*/
@ -2815,8 +2802,8 @@ fs_visitor::compute_to_mrf()
* rewrite the thing that made this GRF to write into the MRF.
*/
foreach_inst_in_block_reverse_starting_from(fs_inst, scan_inst, inst) {
if (scan_inst->dst.file == VGRF &&
scan_inst->dst.nr == inst->src[0].nr) {
if (regions_overlap(scan_inst->dst, scan_inst->regs_written * REG_SIZE,
inst->src[0], inst->regs_read(0) * REG_SIZE)) {
/* Found the last thing to write our reg we want to turn
* into a compute-to-MRF.
*/
@ -2872,53 +2859,32 @@ fs_visitor::compute_to_mrf()
*/
bool interfered = false;
for (int i = 0; i < scan_inst->sources; i++) {
if (scan_inst->src[i].file == VGRF &&
scan_inst->src[i].nr == inst->src[0].nr &&
scan_inst->src[i].reg_offset == inst->src[0].reg_offset) {
if (regions_overlap(scan_inst->src[i], scan_inst->regs_read(i) * REG_SIZE,
inst->src[0], inst->regs_read(0) * REG_SIZE)) {
interfered = true;
}
}
if (interfered)
break;
if (scan_inst->dst.file == MRF) {
if (regions_overlap(scan_inst->dst, scan_inst->regs_written * REG_SIZE,
inst->dst, inst->regs_written * REG_SIZE)) {
/* If somebody else writes our MRF here, we can't
* compute-to-MRF before that.
*/
int scan_mrf_low = scan_inst->dst.nr & ~BRW_MRF_COMPR4;
int scan_mrf_high;
break;
}
if (scan_inst->dst.nr & BRW_MRF_COMPR4) {
scan_mrf_high = scan_mrf_low + 4;
} else if (scan_inst->exec_size == 16) {
scan_mrf_high = scan_mrf_low + 1;
} else {
scan_mrf_high = scan_mrf_low;
}
if (mrf_low == scan_mrf_low ||
mrf_low == scan_mrf_high ||
mrf_high == scan_mrf_low ||
mrf_high == scan_mrf_high) {
break;
}
}
if (scan_inst->mlen > 0 && scan_inst->base_mrf != -1) {
if (scan_inst->mlen > 0 && scan_inst->base_mrf != -1 &&
regions_overlap(fs_reg(MRF, scan_inst->base_mrf), scan_inst->mlen * REG_SIZE,
inst->dst, inst->regs_written * REG_SIZE)) {
/* Found a SEND instruction, which means that there are
* live values in MRFs from base_mrf to base_mrf +
* scan_inst->mlen - 1. Don't go pushing our MRF write up
* above it.
*/
if (mrf_low >= scan_inst->base_mrf &&
mrf_low < scan_inst->base_mrf + scan_inst->mlen) {
break;
}
if (mrf_high >= scan_inst->base_mrf &&
mrf_high < scan_inst->base_mrf + scan_inst->mlen) {
break;
}
}
break;
}
}
}