Thanks folks, publishing now

@grokos any comments here please?
hoping to get this patch in before the 9.0 branch.

thanks for test, LGTM

one follow on question, is there value in adding a testcase for this patch ?

looks like a good change
also consistent with some recent OpenMP language examples committee discussions on this topic.

Superseded by D61313

In D61313#1491568, @hakzsam wrote:

In D61313#1489386, @ronlieb wrote:

This sure does look like the same problem to me. https://reviews.llvm.org/D60459

D60459 doesn't fix the issue.

have you run all the lit tests on this patch ?

This sure does look like the same problem to me. https://reviews.llvm.org/D60459

Added use of LivePhysRegs, happily lifted some code Krzy wrote for Hexagon to compute getLiveRegsAt.

slightly generalized to some physical reg. only look at previous instruction.
The definition is either there, and were all good, or we will bail.

added two MIR tests,and refined logic to properly bail.

Added check for instr match missing, and bail on optimization if so.
I prefer the .ll test we have for the patch now over that of creating an MIR test for this issue.

i think bailing the optimization if not found within some reasonable distance (10 seems to be popular), is a good suggestion. Much better than aborting. thx

The current problem i am trying to resolve in somewhat analogous to hoisting 1/2 of the 64 bit add instruction pair. Although in this particular situation we are actually sinking 1/2 of the instruction pair into a later position within the same block. And yes, i can see how in the future a new machine instruction pass might choose to hoist one of the instructions into a pred BB. I realize i can write additional code to scan a previous block. However i think its better that passes not hoist part of an instruction pair, especially ones such as these. To that end i would rather see my patch assert so that we are forced to deal with such a situation should it arise.
Your example, btw, is a good one for why we should have an IR test for the current problem, rather than an MIR test. An MIR test that runs just before SILoadStoreOptimizer will not detect the affects of a new pass. Whereas the IR test attached to this patch stands a better chance of detecting the issue.

i agree it could happen. Not sure what to do about it here.

after looking at the suggestion of using computeRegisterLiveness, I noticed that it does not return the MI where the register in question is most recently defined.
Rather, it informs on liveness within a range. I don’t really see how I would use this method effectively?
The problem I am trying to solve requires identifying a specific instruction that is needed by a subsequent instruction and then adding the identified instruction to a list constructed by SILoadStoreOptimizer.

correction: the original input test did NOT have the instructions separated by more than 1 or 2 instructions The resultant output showed the large separation.
The default neighborhood of 10 is probably more than enough.

test will convert to MIR form.
Patch will change to use computeRegisterLiveness. i will have to use a pretty large neighborhood , as the original code this error occurred in (before running bugpoint) , had the s_add_u32 instruction was separated by over 400 instructions from the s_addc_u32 instruction. We will assert fail if we cannot find the s_add_u32 instruction, so that will alert us to increase neighborhood size. This patch will also handle the corresponding sub instructions.

LGTM, pending what you decide about adding another lit test.

generally seems fine to me.
Would it be reasonable/useful to have a lit test that somewhat represents what we observed in the DeviceMemory test ?
if you think the fdiv32-to-rcp-folding.ll adequately covers it, then thats fine by me.

next patch

Patch passed our internal jenkins testing: #890

Rebased

Added MIR test, and changes per review comments.

In D54882#1310546, @rampitec wrote:

In D54882#1310543, @ronlieb wrote:

In D54882#1309928, @rampitec wrote:

In D54882#1309888, @ronlieb wrote:

In D54882#1309711, @rampitec wrote:

In D54882#1309708, @ronlieb wrote:

Adding the shrink pass just before Peephole SDWA does not help the lit test, it made no difference.
I think at this point i should proceed with adding the MIR test to verify when we cannot fold.

Do you know why was it unable to shrink these instructions?

SIInstrInfo::splitScalar64BitAddSub converts the S_ADD_U64_PSEUDO into the two add instructions which use the SReg_64_XEXECRegClass instead of VCC.
Later when SIShrinkInstructions::runOnMachineFunction pass runs, it sees that the Carry regs are not VCC and simply marks them with a hint to later convert to VCC ,
and then continues without doing a transformation.

if (SDst) {
  if (SDst->getReg() != AMDGPU::VCC) {
    if (TargetRegisterInfo::isVirtualRegister(SDst->getReg()))
      MRI.setRegAllocationHint(SDst->getReg(), 0, AMDGPU::VCC);
    continue;
  }
 
  // All of the instructions with carry outs also have an SGPR input in
  // src2.
  if (Src2 && Src2->getReg() != AMDGPU::VCC) {
    if (TargetRegisterInfo::isVirtualRegister(Src2->getReg()))
      MRI.setRegAllocationHint(Src2->getReg(), 0, AMDGPU::VCC);
 
    continue;
  }
}

OK, that makes sense. It just leaves it to post-RA shrink that way. Probably shrink pass could do the same, but it is not desirable as it limits scheduling opportunities.

But I see the problem in your code now: you do not check that vcc is not clobbered or used in between of two instructions.
I also think you need to shrink both instructions, otherwise you have carry-in of addc and carry-out of add in different registers, which just happen to be allocated to the same vcc. Note, that isConvertibleToSDWA() returning true does not guarantee final sdwa conversion, so you can end up with vop3 form for the first instruction anyway.

i think the following code does make sure that there are no intervening uses, i can also strengthen it to make sure the defining instruction of the CarryIn is the first ADD instruction.
+ if (!MRI->hasOneUse(CarryIn->getReg()) || !MRI->use_empty(CarryOut->getReg()))
+ return false;

It does not. It only checks that original sreg is not used. However you are replacing original carry sreg with vcc by shrinking instruction, and you do not check vcc uses.

latest approach: transform the pair of ADDs/SUBs into e32, and tighten up check on def/use from one ADD to the other.

In D54882#1309928, @rampitec wrote:

In D54882#1309888, @ronlieb wrote:

In D54882#1309711, @rampitec wrote:

In D54882#1309708, @ronlieb wrote:

Adding the shrink pass just before Peephole SDWA does not help the lit test, it made no difference.
I think at this point i should proceed with adding the MIR test to verify when we cannot fold.

Do you know why was it unable to shrink these instructions?

SIInstrInfo::splitScalar64BitAddSub converts the S_ADD_U64_PSEUDO into the two add instructions which use the SReg_64_XEXECRegClass instead of VCC.
Later when SIShrinkInstructions::runOnMachineFunction pass runs, it sees that the Carry regs are not VCC and simply marks them with a hint to later convert to VCC ,
and then continues without doing a transformation.

if (SDst) {
  if (SDst->getReg() != AMDGPU::VCC) {
    if (TargetRegisterInfo::isVirtualRegister(SDst->getReg()))
      MRI.setRegAllocationHint(SDst->getReg(), 0, AMDGPU::VCC);
    continue;
  }
 
  // All of the instructions with carry outs also have an SGPR input in
  // src2.
  if (Src2 && Src2->getReg() != AMDGPU::VCC) {
    if (TargetRegisterInfo::isVirtualRegister(Src2->getReg()))
      MRI.setRegAllocationHint(Src2->getReg(), 0, AMDGPU::VCC);
 
    continue;
  }
}

OK, that makes sense. It just leaves it to post-RA shrink that way. Probably shrink pass could do the same, but it is not desirable as it limits scheduling opportunities.

But I see the problem in your code now: you do not check that vcc is not clobbered or used in between of two instructions.
I also think you need to shrink both instructions, otherwise you have carry-in of addc and carry-out of add in different registers, which just happen to be allocated to the same vcc. Note, that isConvertibleToSDWA() returning true does not guarantee final sdwa conversion, so you can end up with vop3 form for the first instruction anyway.

In D54882#1309711, @rampitec wrote:

In D54882#1309708, @ronlieb wrote:

Adding the shrink pass just before Peephole SDWA does not help the lit test, it made no difference.
I think at this point i should proceed with adding the MIR test to verify when we cannot fold.

Do you know why was it unable to shrink these instructions?

In D54882#1309642, @rampitec wrote:

In D54882#1309639, @ronlieb wrote:

In D54882#1309605, @rampitec wrote:

In D54882#1309588, @rampitec wrote:

In D54882#1309583, @ronlieb wrote:

In D54882#1308240, @rampitec wrote:

Essentially this is a limited version of shrinking. So I have several questions:

1. Why not to run shrink pass before sdwa instead?

I tried adding Shrink pass before PeepholeSDWA and observed 88 lit test failures.
i tried moving Shrink pass before Peephole SDWA and observed 25 lit test failures

Which may be a good thing if these failures are progressions (as I suspect) and not regressions. Are they progressions?
That is the point of other comments too, this patch is limited to handle just two instructions while there is a clear possibility to do it for almost any VOP3.

I would also assume many of these failures are just commute which is attempted by shrink pass. That is normal and would only need to change the tests.

i tried an experiment of simply invoking the Shrink pass a 2nd time.

addPass(createSIShrinkInstructionsPass());
addPass(createSIShrinkInstructionsPass());

which resulted in 74 failures, and they do seem to be commute changes primarily (did not look at them all)
So then, i added a 3rd invocation and zero failures (i'm still laughing at this one).

So it must be commute. I guess you just need to add a new shrink pass before sdwa. Does it help to deal with these two instructions, e.g. does it help you lit test?

If yes there are two options, either:

1. Revert the commute in shrink pass if it did not help.
2. Just update tests.

In D54882#1309605, @rampitec wrote:

In D54882#1309588, @rampitec wrote:

In D54882#1309583, @ronlieb wrote:

In D54882#1308240, @rampitec wrote:

Essentially this is a limited version of shrinking. So I have several questions:

1. Why not to run shrink pass before sdwa instead?

I tried adding Shrink pass before PeepholeSDWA and observed 88 lit test failures.
i tried moving Shrink pass before Peephole SDWA and observed 25 lit test failures

Which may be a good thing if these failures are progressions (as I suspect) and not regressions. Are they progressions?
That is the point of other comments too, this patch is limited to handle just two instructions while there is a clear possibility to do it for almost any VOP3.

I would also assume many of these failures are just commute which is attempted by shrink pass. That is normal and would only need to change the tests.

Incorporated changes for Some of the Shrink suggestions.
Still need to do an MIR test.
Also, investigate if moving/adding Shrink pass results in test progressions or regressions

In D54882#1308240, @rampitec wrote:

Essentially this is a limited version of shrinking. So I have several questions:

1. Why not to run shrink pass before sdwa instead?

I tried adding Shrink pass before PeepholeSDWA and observed 88 lit test failures.
i tried moving Shrink pass before Peephole SDWA and observed 25 lit test failures

New patch addressing many (but not all) of the review comments.
Will look into the shrink related comments soon ...

New patch arriving momentarily ...

rL347008: [AMDGPU] Add FixupVectorISel pass, currently Supports SREGs in GLOBAL LD/ST

Rebased.

Per review comments, now using getRegBitWidth(),
which exposed a missing case in getRegBitWidth() for AMDGPU::SReg_64_XEXECRegClassID

Added additional comments and some code related to subregs.

Rebased with latest llvm, pushed up to trigger some AMD internal Jenkins testing.
Will work on the subregs suggestions next.

Cleaned up global-saddr.ll test, reducing number of functions, and use addrspace(1) i64

Consolidated 5 tests into 2.
A few minor cleanups on some spacing and indentation.

is this patch worthy of a lit test ?

Cleaned up an if-else statement
Slightly reduced global-saddr-misc.ll

updated global-saddr-misc.ll with instnamer changes

ran instnamer on global-saddr-misc.ll

Thanks Mark , the instnamer suggestion is a good idea. Completed locally, waiting on further review comments from Matt.

added a load/store globals test case (.mir)
updated global-saddr-misc.ll per offline discussion.
changed assert to simpler if (check) continue.

I am planning to add another lit test for coverage of all the Global load/store opcodes.

Revised with various changes to reflect review comments.

Matt, thanks for review, I have addressed most of the issues although the inreg/sgpr one may require some more investigation on my end.
see my responses to each of your review comments.
A revision to this patch will be uploaded in the next hour or so...