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> On Aug 21, 2018, at 17:08, Ryan Taylor via llvm-dev <llvm-dev at lists.llvm.org> 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? > > Thanks. fmad

> On Aug 21, 2018, at 23:06, Ryan Taylor <ryta1203 at gmail.com> wrote: > > Why is isContractableFMUL different from isContractable? If contractable is only expected on the fmul, then what does it even mean to have it set on any other kind of instruction?

For this code: %20 = fmul reassoc nnan arcp contract float %15, %19 %21 = fadd nnan arcp float %20, -1.000000e+00 This does not result in fused multiply-add. it seems like the logic to contact the fmul from the fadd is different than whether to decide to contract the fadd. I would think the logic would be the same for each instruction in the pair. On Tue, Aug 21, 2018 at 2:05 PM Ryan

> 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.

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