similar to: RFC: change -fp-contract=off to actually disable FMAs

I'm curious why the condition to fuse is this: // Floating-point multiply-add with intermediate rounding. bool HasFMAD = (LegalOperations && TLI.isOperationLegal(ISD::FMAD, VT)); static bool isContractable(SDNode *N) { SDNodeFlags F = N->getFlags(); return F.hasAllowContract() || F.hasAllowReassociation(); } bool CanFuse = Options.UnsafeFPMath || isContractable(N); bool

On 21.08.2018 16:08, Ryan Taylor via llvm-dev wrote: > So I have a test case where: > > %20 = fmul nnan arcp float %15, %19 > %21 = fadd reassoc nnan arcp contract float %20, -1.000000e+00 > > is being contracted in DAG to fmad. Is this correct since the fmul has > no reassoc or contract fast math flag? By having the reassoc and contract flags on fadd, the frontend is

On 22.08.2018 17:52, Ryan Taylor wrote: > This is probably going to effect on other backends and break llvm-lit > for them? Very likely, yes. Can you take a look at how big the fallout is? This might give us a hint about what other frontends might expect, and who needs to be involved in the discussion (if one is needed). Cheers, Nicolai > > On Wed, Aug 22, 2018 at 11:41 AM

On 22.08.2018 13:29, Ryan Taylor wrote: > The example starts as SPIR-V with the NoContraction decoration flag on > the fmul. > > I think what you are saying seems valid in that if the user had put the > flag on the fadd instead of the fmul it would not contract and so in > this example the user needs to put the NoContraction on the fadd though > I'm not sure

Maybe there is a cleaner solution but it seems like adding a 'nocontract' flag is close to the intention of spir-v and is an easy check in the DAGCombiner without breaking anything else and its intentions are very clear. Right now the DAGCombiner logic doesn't seem to be able to handle the case of having fast math globally with instruction level flags to turn off fast math. Right now,

Michael, >From the spec with regards to reassoc: – 15225 Include no re-association as a constraint required by the NoContraction Decoration. I don't see a solution given the situation where -fp-contract=fast and we want to contract. Furthermore, I think a 'nocontract' flag will allow the IR to be more readable in it's intention. The problem is you can have 2 fp arith

Nicolai, Can you do without the use of -fp-contract=fast (Options.AllowFPOpFusion == FPOpFusion::Fast ) and without Unsafe? As I SPIR-V’s usage of NoContraction flies in the face of both. If so, you should be able to get what you want, as then you are down to just IR flags. You will need a model to generate the correct behavior though in your SPIR-V implementation wrt IR flag emissions.

I don't think the global fast math flag should override the NoContraction decoration as that's mostly the point of that decoration to begin with, to have fine granular control while still having a broad sweeping optimization. Did I miss your point? I feel like I did. On Thu, Aug 23, 2018, 3:42 PM Michael Berg <michael_c_berg at apple.com> wrote: > Ryan, > > Given that the

Numerically identical, sure. But, there are other reasons to disable FMAD fusion -- namely for performance comparisons. On Wed, Jul 10, 2019 at 2:52 PM Matt Arsenault <arsenm2 at gmail.com> wrote: > > > On Jul 10, 2019, at 15:27, Scott Manley via llvm-dev < > llvm-dev at lists.llvm.org> wrote: > > Is there context I am not aware of for ::Strict and ISD::FMAD? I

> That's not typically something we'd expose to the end user in any way. > Clang as a compiler should be selecting what it thinks is the fastest > sequence to do some particular job; if it's wrong then that's a bug, > not something to add a command-line flag for. I can't agree with that as a general statement. How is it any different than giving the user the

> I think you have a different definition of fused then. Fused is a description of how the operation is computed/rounded, not an instruction count. "Only fuse FP ops when the result won't be affected" is what the existing comment says. So it can't be both a fused op and not a fused op if it's only meant to imply a difference in rounding. I'm just re-using the

> However, fp-contract is not a knob to control whether or not abstract-machine operations generate a single arithmetic instruction I think that makes sense, but the end result is the same. Wouldn't you agree that -fp-contract=off still contracts floating point expressions with the initial example I posted? That is the core of what I'm trying to resolve here. I still have some

Hal Finkel <hfinkel at anl.gov> writes: > There are a few conditions that contribute to the decision of whether > or not to make the fmuladd -> fma translation. The relevant code is in > CodeGen/SelectionDAG/SelectionDAGBuilder.cpp: > > case Intrinsic::fmuladd: { > EVT VT = TLI.getValueType(I.getType()); > if (TM.Options.AllowFPOpFusion !=

----- Original Message ----- > From: "Cameron McInally" <cameron.mcinally at nyu.edu> > To: "Andrew Booker" <andrew.booker at arm.com> > Cc: llvmdev at cs.uiuc.edu > Sent: Friday, January 11, 2013 12:37:07 PM > Subject: Re: [LLVMdev] Documentation of fmuladd intrinsic > > > On Fri, Jan 11, 2013 at 1:08 PM, Andrew Booker < >

> On Jan 28, 2015, at 3:47 PM, Hal Finkel <hfinkel at anl.gov> wrote: > > ----- Original Message ----- >> From: "Matt Arsenault" <Matthew.Arsenault at amd.com> >> To: "llvmdev at cs.uiuc.edu" <LLVMdev at cs.uiuc.edu> >> Sent: Wednesday, January 28, 2015 1:52:59 PM >> Subject: [LLVMdev] RFC: Add ISD nodes for mad >>

> On Aug 21, 2018, at 17:57, Ryan Taylor <ryta1203 at gmail.com> wrote: > > Matt, > I'm sorry, actually it's fma not fmad. > > In the post-legalizer DAG combine for the given code it's producing fma not fmad. That doens't seem correct. > The contract is on the fadd. I’m not really sure what the rule is supposed to be for contract between the nodes.

----- Original Message ----- > From: "Sanjay Patel" <spatel at rotateright.com> > To: "Hal J. Finkel" <hfinkel at anl.gov> > Cc: "Mehdi Amini" <mehdi.amini at apple.com>, "llvm-dev" > <llvm-dev at lists.llvm.org>, "cfe-dev" <cfe-dev at lists.llvm.org>, > "andrew kaylor" <andrew.kaylor at

On Fri, Jan 11, 2013 at 1:08 PM, Andrew Booker <andrew.booker at arm.com>wrote: > The fmuladd intrinsic is described as saying that a multiply and > addition sequence can be fused into an fma instruction "if the code > generator determines that the fused expression would be legal and > efficient". (http://llvm.org/docs/LangRef.html#llvm-fma-intrinsic) > >

Out of curiosity, what is the use-case for isFMAFasterThanMulAndAdd? If a target declares that FMA is actually slower for a given type, why not just declare it as illegal for that type? Wouldn't that accomplish the same thing without another target hook? I feel like I'm missing something here. On Fri, Jan 11, 2013 at 2:40 PM, Hal Finkel <hfinkel at anl.gov> wrote: > -----

Sent from my Verizon Wireless 4G LTE DROID On Nov 17, 2016 5:53 PM, Mehdi Amini <mehdi.amini at apple.com<mailto:mehdi.amini at apple.com>> wrote: > > >> On Nov 17, 2016, at 4:33 PM, Hal Finkel <hfinkel at anl.gov<mailto:hfinkel at anl.gov>> wrote: >> >> >> ________________________________ >>> >>> From: "Warren