Arsenault, Matthew via llvm-dev
2019-Feb-05 13:58 UTC
[llvm-dev] [RFC] Enforcing immediate operands for intrinsics
Hi, I would like to solve the longstanding need for a way to indicate which parameters to an intrinsic are required to be immediates. It should be possible to declare in tablegen which parameters must be a trivial constant, or else the IR is invalid. The verifier could then reject invalid intrinsic calls, so code handling the intrinsics doesn’t need to worry about invalid arguments. Currently any code that deals with such intrinsics needs to do type checks on the argument to avoid crashing on valid IR. This isn’t done particularly consistently (e.g. see r352904, or the follow-up r353097 for a recent example fix). From the codegen side, we do things like folding invalid intrinsic calls to undef during custom lowering, which is more boilerplate which shouldn’t be necessary. It’s also necessary in a few some passes to know it’s illegal to replace an argument with a constant. llvm::canReplaceOperandWithVariable currently has to conservatively assume any intrinsic arguments can’t be touched. I have 2 versions of partial implementations of this. 1. Uses a new intrinsic query table to return a bitmask of which operands need to be constant 2. Introduces a new parameter attribute My current preference is for option 2. I initially expected to create the table, but then I was creating an uglier way of tracking parameter properties that exactly tracked alongside the attribute handling. It seems cleaner to just put it there, even though it seems a bit overkill and looks slightly strange. The rules for the attribute will look like: * Only allowed on intrinsics declarations. It is not allowed on an arbitrary function * Not allowed on individual call sites * The parameter must be a trivial constant leaf (i.e. ConstantInt, ConstantFP, or Undef). No aggregates or vectors are allowed * It will be incompatible with all other parameter attributes such as sret or returned For bikeshedding the name, I’m currently calling the attribute “constant”, but I think this is a bad name. It doesn’t allow arbitrary constants (such as ConstantExprs), so I think something more like “immarg” ‘or “immediate” would be better. -Matt -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20190205/d7265fbb/attachment.html>
Eli Friedman via llvm-dev
2019-Feb-05 18:55 UTC
[llvm-dev] [RFC] Enforcing immediate operands for intrinsics
Adding an "immarg" attribute makes sense; thanks for working on this. -Eli ________________________________ From: llvm-dev <llvm-dev-bounces at lists.llvm.org> on behalf of Arsenault, Matthew via llvm-dev <llvm-dev at lists.llvm.org> Sent: Tuesday, February 5, 2019 5:58 AM To: llvm-dev Subject: [EXT] [llvm-dev] [RFC] Enforcing immediate operands for intrinsics Hi, I would like to solve the longstanding need for a way to indicate which parameters to an intrinsic are required to be immediates. It should be possible to declare in tablegen which parameters must be a trivial constant, or else the IR is invalid. The verifier could then reject invalid intrinsic calls, so code handling the intrinsics doesn't need to worry about invalid arguments. Currently any code that deals with such intrinsics needs to do type checks on the argument to avoid crashing on valid IR. This isn't done particularly consistently (e.g. see r352904, or the follow-up r353097 for a recent example fix). From the codegen side, we do things like folding invalid intrinsic calls to undef during custom lowering, which is more boilerplate which shouldn't be necessary. It's also necessary in a few some passes to know it's illegal to replace an argument with a constant. llvm::canReplaceOperandWithVariable currently has to conservatively assume any intrinsic arguments can't be touched. I have 2 versions of partial implementations of this. 1. Uses a new intrinsic query table to return a bitmask of which operands need to be constant 2. Introduces a new parameter attribute My current preference is for option 2. I initially expected to create the table, but then I was creating an uglier way of tracking parameter properties that exactly tracked alongside the attribute handling. It seems cleaner to just put it there, even though it seems a bit overkill and looks slightly strange. The rules for the attribute will look like: * Only allowed on intrinsics declarations. It is not allowed on an arbitrary function * Not allowed on individual call sites * The parameter must be a trivial constant leaf (i.e. ConstantInt, ConstantFP, or Undef). No aggregates or vectors are allowed * It will be incompatible with all other parameter attributes such as sret or returned For bikeshedding the name, I'm currently calling the attribute "constant", but I think this is a bad name. It doesn't allow arbitrary constants (such as ConstantExprs), so I think something more like "immarg" 'or "immediate" would be better. -Matt -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20190205/02eb11a3/attachment-0001.html>
Finkel, Hal J. via llvm-dev
2019-Feb-05 22:44 UTC
[llvm-dev] [RFC] Enforcing immediate operands for intrinsics
On 2/5/19 12:55 PM, Eli Friedman via llvm-dev wrote: Adding an "immarg" attribute makes sense; thanks for working on this. +1 -Hal -Eli ________________________________ From: llvm-dev <llvm-dev-bounces at lists.llvm.org><mailto:llvm-dev-bounces at lists.llvm.org> on behalf of Arsenault, Matthew via llvm-dev <llvm-dev at lists.llvm.org><mailto:llvm-dev at lists.llvm.org> Sent: Tuesday, February 5, 2019 5:58 AM To: llvm-dev Subject: [EXT] [llvm-dev] [RFC] Enforcing immediate operands for intrinsics Hi, I would like to solve the longstanding need for a way to indicate which parameters to an intrinsic are required to be immediates. It should be possible to declare in tablegen which parameters must be a trivial constant, or else the IR is invalid. The verifier could then reject invalid intrinsic calls, so code handling the intrinsics doesn’t need to worry about invalid arguments. Currently any code that deals with such intrinsics needs to do type checks on the argument to avoid crashing on valid IR. This isn’t done particularly consistently (e.g. see r352904, or the follow-up r353097 for a recent example fix). From the codegen side, we do things like folding invalid intrinsic calls to undef during custom lowering, which is more boilerplate which shouldn’t be necessary. It’s also necessary in a few some passes to know it’s illegal to replace an argument with a constant. llvm::canReplaceOperandWithVariable currently has to conservatively assume any intrinsic arguments can’t be touched. I have 2 versions of partial implementations of this. 1. Uses a new intrinsic query table to return a bitmask of which operands need to be constant 2. Introduces a new parameter attribute My current preference is for option 2. I initially expected to create the table, but then I was creating an uglier way of tracking parameter properties that exactly tracked alongside the attribute handling. It seems cleaner to just put it there, even though it seems a bit overkill and looks slightly strange. The rules for the attribute will look like: * Only allowed on intrinsics declarations. It is not allowed on an arbitrary function * Not allowed on individual call sites * The parameter must be a trivial constant leaf (i.e. ConstantInt, ConstantFP, or Undef). No aggregates or vectors are allowed * It will be incompatible with all other parameter attributes such as sret or returned For bikeshedding the name, I’m currently calling the attribute “constant”, but I think this is a bad name. It doesn’t allow arbitrary constants (such as ConstantExprs), so I think something more like “immarg” ‘or “immediate” would be better. -Matt _______________________________________________ LLVM Developers mailing list llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev -- Hal Finkel Lead, Compiler Technology and Programming Languages Leadership Computing Facility Argonne National Laboratory -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://lists.llvm.org/pipermail/llvm-dev/attachments/20190205/7097ec58/attachment.html>
Krzysztof Parzyszek via llvm-dev
2019-Feb-05 23:55 UTC
[llvm-dev] [RFC] Enforcing immediate operands for intrinsics
There is something similar going on in clang in SemaChecking.cpp. The difference is that each target can write its own verification code, which may check things like value ranges, for example. The scheme you're proposing would invent a new attribute (a widespread change) that only implements partial checks (i.e. "is argument immediate or not"). Why not simply add a function to TTI that tells you whether a particular Value is a valid n-th argument to the given intrinsic? Something like if (TTI.isValidArgument(IntOpc, Val, OpIdx)) Int->setOperand(Val, OpIdx); -Krzysztof On 2/5/2019 7:58 AM, Arsenault, Matthew via llvm-dev wrote:> Hi, > > I would like to solve the longstanding need for a way to indicate which > parameters to an intrinsic are required to be immediates. It should be > possible to declare in tablegen which parameters must be a trivial > constant, or else the IR is invalid. > > The verifier could then reject invalid intrinsic calls, so code handling > the intrinsics doesn’t need to worry about invalid arguments. Currently > any code that deals with such intrinsics needs to do type checks on the > argument to avoid crashing on valid IR. This isn’t done particularly > consistently (e.g. see r352904, or the follow-up r353097 for a recent > example fix). From the codegen side, we do things like folding invalid > intrinsic calls to undef during custom lowering, which is more > boilerplate which shouldn’t be necessary. > > It’s also necessary in a few some passes to know it’s illegal to replace > an argument with a constant. llvm::canReplaceOperandWithVariable > currently has to conservatively assume any intrinsic arguments can’t be > touched. > > I have 2 versions of partial implementations of this. > > 1. Uses a new intrinsic query table to return a bitmask of which > operands need to be constant > 2. Introduces a new parameter attribute > > My current preference is for option 2. I initially expected to create > the table, but then I was creating an uglier way of tracking parameter > properties that exactly tracked alongside the attribute handling. It > seems cleaner to just put it there, even though it seems a bit overkill > and looks slightly strange. > > The rules for the attribute will look like: > > * Only allowed on intrinsics declarations. It is not allowed on an > arbitrary function > * Not allowed on individual call sites > * The parameter must be a trivial constant leaf (i.e. ConstantInt, > ConstantFP, or Undef). No aggregates or vectors are allowed > * It will be incompatible with all other parameter attributes such as > sret or returned > > For bikeshedding the name, I’m currently calling the attribute > “constant”, but I think this is a bad name. It doesn’t allow arbitrary > constants (such as ConstantExprs), so I think something more like > “immarg” ‘or “immediate” would be better. > > -Matt > > > <http://www.avg.com/email-signature?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=emailclient> > Virus-free. www.avg.com > <http://www.avg.com/email-signature?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=emailclient> > > > <#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2> > > _______________________________________________ > LLVM Developers mailing list > llvm-dev at lists.llvm.org > https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev >
Matt Arsenault via llvm-dev
2019-Feb-06 00:17 UTC
[llvm-dev] [RFC] Enforcing immediate operands for intrinsics
> On Feb 5, 2019, at 6:55 PM, Krzysztof Parzyszek via llvm-dev <llvm-dev at lists.llvm.org> wrote: > > There is something similar going on in clang in SemaChecking.cpp. The difference is that each target can write its own verification code, which may check things like value ranges, for example. > The scheme you're proposing would invent a new attribute (a widespread change) that only implements partial checks (i.e. "is argument immediate or not”).This is for the benefit of IR transform passes and codegen. I’m not attempting to diagnose frontend builtins or do anything for the end user. A backend can always truncate bits or whatever to fit the actual instruction constraints if necessary. It has to do something to not crash on the IR otherwise, which is part of the problem I’m trying to solve.> > Why not simply add a function to TTI that tells you whether a particular Value is a valid n-th argument to the given intrinsic? > Something like > if (TTI.isValidArgument(IntOpc, Val, OpIdx)) > Int->setOperand(Val, OpIdx); >This is required for correctness, so TTI is not appropriate. Reasonably implementing this would still require adding something in TableGen (which then just brings you back to adding an attribute). I would also like to be able to rely on this for emission of G_INTRINISIC_* instructions in GlobalISel, so that intermediate illegal G_CONSTANT instructions can be avoided -Matt
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