Re: [Mesa-dev] i965: overwriting parts of a register and optimization passes
Hi Kenneth,
El 2014-07-09 17:19, Kenneth Graunke escribió:
On Tuesday, July 08, 2014 11:19:38 AM Iago Toral wrote:
Hi,
I have some code that first initializes a register and then
overwrites a
specific subregister. However, after the optimization passes in
brw_vec4.cpp the initialization instruction goes away. I see that
live
intervals are computed for the destination register without
considering
if we are writing only to a specific subregister, so I guess that is
the
reason for this behaviour, but this strikes me as odd, as it defeats
the
purpose of overwriting only specific subregs, so I guess there is
something else that I am missing.
This an example of what is happening:
mov(8) g61.xUD g04,4,1UD {
align16 WE_all 1Q };
mov(1) g6.21UD 0x0007UD { align1
WE_all compacted };
The first MOV is removed from the instruction set when I put the
second
MOV, however the second MOV should only be writing to subreg 6.2 and
keep the rest of register 6 intact, or at least that is what I am
trying
to do...
Can someone explain what is wrong with those two instructions? how
should I overwrite only a specific subregister without causing this
behavior?
Thanks,
Iago
This sounds a lot like the bug I fixed in:
commit d0575d98fc595dcc17706dc73d1eb461027ca17a
Author: Kenneth Graunke kenn...@whitecape.org
Date: Sat Jun 14 03:53:07 2014 -0700
i965/vec4: Fix dead code elimination for VGRFs of size 1.
where it would see those two as the same register, and delete the
first MOV.
You probably already have that in your tree though, right? If not,
update :)
Yeah, I have it already, so I guess my problem was different.
If so, you might try turning off other optimization passes in
brw_vec4.cpp and see if it helps - sounds like a bug in one of them.
The one causing that behaviour was the dead code elimination pass in
brw_vec4.cpp. Anyway, this is not happening consistently, I have done
some changes to my code that are unrelated to these two instructions and
now this is not happening any more...
Iago
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Re: [Mesa-dev] i965: overwriting parts of a register and optimization passes
On Tuesday, July 08, 2014 11:19:38 AM Iago Toral wrote:
Hi,
I have some code that first initializes a register and then overwrites a
specific subregister. However, after the optimization passes in
brw_vec4.cpp the initialization instruction goes away. I see that live
intervals are computed for the destination register without considering
if we are writing only to a specific subregister, so I guess that is the
reason for this behaviour, but this strikes me as odd, as it defeats the
purpose of overwriting only specific subregs, so I guess there is
something else that I am missing.
This an example of what is happening:
mov(8) g61.xUD g04,4,1UD {
align16 WE_all 1Q };
mov(1) g6.21UD 0x0007UD{ align1
WE_all compacted };
The first MOV is removed from the instruction set when I put the second
MOV, however the second MOV should only be writing to subreg 6.2 and
keep the rest of register 6 intact, or at least that is what I am trying
to do...
Can someone explain what is wrong with those two instructions? how
should I overwrite only a specific subregister without causing this
behavior?
Thanks,
Iago
This sounds a lot like the bug I fixed in:
commit d0575d98fc595dcc17706dc73d1eb461027ca17a
Author: Kenneth Graunke kenn...@whitecape.org
Date: Sat Jun 14 03:53:07 2014 -0700
i965/vec4: Fix dead code elimination for VGRFs of size 1.
where it would see those two as the same register, and delete the first MOV.
You probably already have that in your tree though, right? If not, update :)
If so, you might try turning off other optimization passes in brw_vec4.cpp and
see if it helps - sounds like a bug in one of them.
--Ken
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Re: [Mesa-dev] i965: overwriting parts of a register and optimization passes
On Wed, Jul 9, 2014 at 8:19 AM, Kenneth Graunke kenn...@whitecape.org wrote:
On Tuesday, July 08, 2014 11:19:38 AM Iago Toral wrote:
Hi,
I have some code that first initializes a register and then overwrites a
specific subregister. However, after the optimization passes in
brw_vec4.cpp the initialization instruction goes away. I see that live
intervals are computed for the destination register without considering
if we are writing only to a specific subregister, so I guess that is the
reason for this behaviour, but this strikes me as odd, as it defeats the
purpose of overwriting only specific subregs, so I guess there is
something else that I am missing.
This an example of what is happening:
mov(8) g61.xUD g04,4,1UD {
align16 WE_all 1Q };
mov(1) g6.21UD 0x0007UD { align1
WE_all compacted };
The first MOV is removed from the instruction set when I put the second
MOV, however the second MOV should only be writing to subreg 6.2 and
keep the rest of register 6 intact, or at least that is what I am trying
to do...
Can someone explain what is wrong with those two instructions? how
should I overwrite only a specific subregister without causing this
behavior?
Thanks,
Iago
This sounds a lot like the bug I fixed in:
commit d0575d98fc595dcc17706dc73d1eb461027ca17a
Author: Kenneth Graunke kenn...@whitecape.org
Date: Sat Jun 14 03:53:07 2014 -0700
i965/vec4: Fix dead code elimination for VGRFs of size 1.
where it would see those two as the same register, and delete the first MOV.
You probably already have that in your tree though, right? If not, update :)
If so, you might try turning off other optimization passes in brw_vec4.cpp
and see if it helps - sounds like a bug in one of them.
Or you could add something like Matts DEBUG_OPTIMIZER from brw_fs.cpp
to also cover brw_vec4.cpp.
Kristian
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[Mesa-dev] i965: overwriting parts of a register and optimization passes
Hi,
I have some code that first initializes a register and then overwrites a
specific subregister. However, after the optimization passes in
brw_vec4.cpp the initialization instruction goes away. I see that live
intervals are computed for the destination register without considering
if we are writing only to a specific subregister, so I guess that is the
reason for this behaviour, but this strikes me as odd, as it defeats the
purpose of overwriting only specific subregs, so I guess there is
something else that I am missing.
This an example of what is happening:
mov(8) g61.xUD g04,4,1UD {
align16 WE_all 1Q };
mov(1) g6.21UD 0x0007UD{ align1
WE_all compacted };
The first MOV is removed from the instruction set when I put the second
MOV, however the second MOV should only be writing to subreg 6.2 and
keep the rest of register 6 intact, or at least that is what I am trying
to do...
Can someone explain what is wrong with those two instructions? how
should I overwrite only a specific subregister without causing this
behavior?
Thanks,
Iago
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