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intel/fs: Fix flag_subreg handling in cmod propagation

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There were two errors.  First, the pass could propagate conditional
modifiers from an instruction that writes on flag register to an
instruction that writes a different flag register.  For example,

    cmp.nz.f0.0(16) null:F, vgrf6:F, vgrf5:F
    cmp.nz.f0.1(16) null:F, vgrf6:F, vgrf5:F

could be come

    cmp.nz.f0.0(16) null:F, vgrf6:F, vgrf5:F

Second, if an instruction writes f0.1 has it's condition propagated, the
modified instruction will incorrectly write flag f0.0.  For example,

    linterp(16) vgrf6:F, g2:F, attr0:F
    cmp.z.f0.1(16) null:F, vgrf6:F, vgrf5:F
    (-f0.1) discard_jump(16) (null):UD

could become

    linterp.z.f0.0(16) vgrf6:F, g2:F, attr0:F
    (-f0.1) discard_jump(16) (null):UD

None of these cases will occur currently.  The only time we use f0.1 is
for generating discard intrinsics.  In all those cases, we generate a
squence like:

    cmp.nz.f0.0(16) vgrf7:F, vgrf6:F, vgrf5:F
    (+f0.1) cmp.z(16) null:D, vgrf7:D, 0d
    (-f0.1) discard_jump(16) (null):UD

Due to the mixed types and incompatible conditions, this sequence would
never see any cmod propagation.  The next patch will change this.

No shader-db changes on any Intel platform.

v2: Fix typo in comment in test case subtract_delete_compare_other_flag.
Noticed by Caio.

Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>
This commit is contained in:
Ian Romanick
2019-05-22 10:18:06 -07:00
parent 2dd6013933
commit 8030cb75c1
2 changed files with 196 additions and 0 deletions
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37
src/intel/compiler/brw_fs_cmod_propagation.cpp
View File

@@ -53,6 +53,7 @@ cmod_propagate_cmp_to_add(const gen_device_info *devinfo, bblock_t *block,
fs_inst *inst)
{
bool read_flag = false;
const unsigned flags_written = inst->flags_written();
foreach_inst_in_block_reverse_starting_from(fs_inst, scan_inst, inst) {
if (scan_inst->opcode == BRW_OPCODE_ADD &&
@@ -79,6 +80,17 @@ cmod_propagate_cmp_to_add(const gen_device_info *devinfo, bblock_t *block,
goto not_match;
}
/* If the scan instruction writes a different flag register than the
* instruction we're trying to propagate from, bail.
*
* FINISHME: The second part of the condition may be too strong.
* Perhaps (scan_inst->flags_written() & flags_written) !=
* flags_written?
*/
if (scan_inst->flags_written() != 0 &&
scan_inst->flags_written() != flags_written)
goto not_match;
/* From the Sky Lake PRM Vol. 7 "Assigning Conditional Mods":
*
* * Note that the [post condition signal] bits generated at
@@ -130,6 +142,7 @@ cmod_propagate_not(const gen_device_info *devinfo, bblock_t *block,
{
const enum brw_conditional_mod cond = brw_negate_cmod(inst->conditional_mod);
bool read_flag = false;
const unsigned flags_written = inst->flags_written();
if (cond != BRW_CONDITIONAL_Z && cond != BRW_CONDITIONAL_NZ)
return false;
@@ -146,6 +159,17 @@ cmod_propagate_not(const gen_device_info *devinfo, bblock_t *block,
scan_inst->exec_size != inst->exec_size)
break;
/* If the scan instruction writes a different flag register than the
* instruction we're trying to propagate from, bail.
*
* FINISHME: The second part of the condition may be too strong.
* Perhaps (scan_inst->flags_written() & flags_written) !=
* flags_written?
*/
if (scan_inst->flags_written() != 0 &&
scan_inst->flags_written() != flags_written)
break;
if (scan_inst->can_do_cmod() &&
((!read_flag && scan_inst->conditional_mod == BRW_CONDITIONAL_NONE) ||
scan_inst->conditional_mod == cond)) {
@@ -231,9 +255,21 @@ opt_cmod_propagation_local(const gen_device_info *devinfo, bblock_t *block)
}
bool read_flag = false;
const unsigned flags_written = inst->flags_written();
foreach_inst_in_block_reverse_starting_from(fs_inst, scan_inst, inst) {
if (regions_overlap(scan_inst->dst, scan_inst->size_written,
inst->src[0], inst->size_read(0))) {
/* If the scan instruction writes a different flag register than
* the instruction we're trying to propagate from, bail.
*
* FINISHME: The second part of the condition may be too strong.
* Perhaps (scan_inst->flags_written() & flags_written) !=
* flags_written?
*/
if (scan_inst->flags_written() != 0 &&
scan_inst->flags_written() != flags_written)
break;
if (scan_inst->is_partial_write() ||
scan_inst->dst.offset != inst->src[0].offset ||
scan_inst->exec_size != inst->exec_size)
@@ -380,6 +416,7 @@ opt_cmod_propagation_local(const gen_device_info *devinfo, bblock_t *block)
((!read_flag && scan_inst->conditional_mod == BRW_CONDITIONAL_NONE) ||
scan_inst->conditional_mod == cond)) {
scan_inst->conditional_mod = cond;
scan_inst->flag_subreg = inst->flag_subreg;
inst->remove(block);
progress = true;
}