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intel/compiler: fix cmod propagation optimisations

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Knowing following:
 - CMP writes to flag register the result of
   applying cmod to the `src0 - src1`.
   After that it stores the same value to dst.
   Other instructions first store their result to
   dst, and then store cmod(dst) to the flag
   register.
 - inst is either CMP or MOV
 - inst->dst is null
 - inst->src[0] overlaps with scan_inst->dst
 - inst->src[1] is zero
 - scan_inst wrote to a flag register

There can be three possible paths:

 - scan_inst is CMP:

   Considering that src0 is either 0x0 (false),
   or 0xffffffff (true), and src1 is 0x0:

   - If inst's cmod is NZ, we can always remove
     scan_inst: NZ is invariant for false and true. This
     holds even if src0 is NaN: .nz is the only cmod,
     that returns true for NaN.

   - .g is invariant if src0 has a UD type

   - .l is invariant if src0 has a D type

 - scan_inst and inst have the same cmod:

   If scan_inst is anything than CMP, it already
   wrote the appropriate value to the flag register.

 - else:

   We can change cmod of scan_inst to that of inst,
   and remove inst. It is valid as long as we make
   sure that no instruction uses the flag register
   between scan_inst and inst.

Nine new cmod_propagation unit tests:
 - cmp_cmpnz
 - cmp_cmpg
 - plnnz_cmpnz
 - plnnz_cmpz (*)
 - plnnz_sel_cmpz
 - cmp_cmpg_D
 - cmp_cmpg_UD (*)
 - cmp_cmpl_D (*)
 - cmp_cmpl_UD

(*) this would fail without changes to brw_fs_cmod_propagation.

This fixes optimisation that used to be illegal (see issue #2154)

= Before =
 0: linterp.z.f0.0(8) vgrf0:F, g2:F, attr0<0>:F
 1: cmp.nz.f0.0(8) null:F, vgrf0:F, 0f
= After =
 0: linterp.z.f0.0(8) vgrf0:F, g2:F, attr0<0>:F

Now it is optimised as such (note change of cmod in line 0):

= Before =
 0: linterp.z.f0.0(8) vgrf0:F, g2:F, attr0<0>:F
 1: cmp.nz.f0.0(8) null:F, vgrf0:F, 0f
= After =
 0: linterp.nz.f0.0(8) vgrf0:F, g2:F, attr0<0>:F

No shaderdb changes

Closes: https://gitlab.freedesktop.org/mesa/mesa/issues/2154

Signed-off-by: Yevhenii Kolesnikov <yevhenii.kolesnikov@globallogic.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/3348>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/3348>
This commit is contained in:
Yevhenii Kolesnikov
2020-01-03 16:37:00 +02:00
committed by Marge Bot
parent 3b76b3bc09
commit 32b7ba66b0
2 changed files with 336 additions and 9 deletions
Download Patch File Download Diff File Expand all files Collapse all files

70
src/intel/compiler/brw_fs_cmod_propagation.cpp
View File

@@ -328,17 +328,69 @@ opt_cmod_propagation_local(const gen_device_info *devinfo, bblock_t *block)
}
}
/* If the instruction generating inst's source also wrote the
* flag, and inst is doing a simple .nz comparison, then inst
* is redundant - the appropriate value is already in the flag
* register. Delete inst.
/* Knowing following:
* - CMP writes to flag register the result of
* applying cmod to the `src0 - src1`.
* After that it stores the same value to dst.
* Other instructions first store their result to
* dst, and then store cmod(dst) to the flag
* register.
* - inst is either CMP or MOV
* - inst->dst is null
* - inst->src[0] overlaps with scan_inst->dst
* - inst->src[1] is zero
* - scan_inst wrote to a flag register
*
* There can be three possible paths:
*
* - scan_inst is CMP:
*
* Considering that src0 is either 0x0 (false),
* or 0xffffffff (true), and src1 is 0x0:
*
* - If inst's cmod is NZ, we can always remove
* scan_inst: NZ is invariant for false and true. This
* holds even if src0 is NaN: .nz is the only cmod,
* that returns true for NaN.
*
* - .g is invariant if src0 has a UD type
*
* - .l is invariant if src0 has a D type
*
* - scan_inst and inst have the same cmod:
*
* If scan_inst is anything than CMP, it already
* wrote the appropriate value to the flag register.
*
* - else:
*
* We can change cmod of scan_inst to that of inst,
* and remove inst. It is valid as long as we make
* sure that no instruction uses the flag register
* between scan_inst and inst.
*/
if (inst->conditional_mod == BRW_CONDITIONAL_NZ &&
!inst->src[0].negate &&
if (!inst->src[0].negate &&
scan_inst->flags_written()) {
inst->remove(block);
progress = true;
break;
if (scan_inst->opcode == BRW_OPCODE_CMP) {
if ((inst->conditional_mod == BRW_CONDITIONAL_NZ) ||
(inst->conditional_mod == BRW_CONDITIONAL_G &&
inst->src[0].type == BRW_REGISTER_TYPE_UD) ||
(inst->conditional_mod == BRW_CONDITIONAL_L &&
inst->src[0].type == BRW_REGISTER_TYPE_D)) {
inst->remove(block);
progress = true;
break;
}
} else if (scan_inst->conditional_mod == inst->conditional_mod) {
inst->remove(block);
progress = true;
break;
} else if (!read_flag) {
scan_inst->conditional_mod = inst->conditional_mod;
inst->remove(block);
progress = true;
break;
}
}
/* The conditional mod of the CMP/CMPN instructions behaves