r201439 - [CodeGenPrepare][AddressingModeMatcher] Give up on type promotion if the

Wed Feb 19 11:51:02 PST 2014

On Wed, Feb 19, 2014 at 11:29:43AM -0800, Quentin Colombet wrote:
> Hi Tom,
> 
> That’s weird that bugpoint is linking correctly for you.

I just realized that it's probably working for me because I
build with --enable-shared.

> 
> I have dug in that linking problem and here is what I found.
> Because of the CodeGenPrepare pass, libLLVMScalarOpts has a dependency on libLLVMCodeGen, which is not included on the link command of bugpoint.
> 
> So far it was working because all the functions of TargetLowering called in CodeGenPrepare are either:
> - virtual function (resolved dynamically).
> - inlined in the header (code available statically).
> 
> InstructionOpcodeToISD is not a virtual function and not inlined in the header, thus the linking problem.
> 
> We could add a dependency in bugpoint on libLLVMCodeGen, but I am not sure we want to do that.

This seems to me like the best solution.  What are the disadvantages to doing this?

-Tom

> Another possibility would be to inline InstructionOpcodeToISD into the header, though I haven’t check how much this is pulling into the header.
> 
> Thoughts?
> 
> Cheers,
> -Quentin
> 
> On Feb 18, 2014, at 2:28 PM, Tom Stellard <tom at stellard.net> wrote:
> 
> > On Tue, Feb 18, 2014 at 12:45:33PM -0800, Quentin Colombet wrote:
> >> 
> >> On Feb 18, 2014, at 11:19 AM, Tom Stellard <tom at stellard.net> wrote:
> >> 
> >>> On Tue, Feb 18, 2014 at 11:00:05AM -0800, Quentin Colombet wrote:
> >>>> 
> >>>> On Feb 18, 2014, at 10:30 AM, Tom Stellard <tom at stellard.net> wrote:
> >>>> 
> >>>>> On Tue, Feb 18, 2014 at 09:47:21AM -0800, Quentin Colombet wrote:
> >>>>>> 
> >>>>>> On Feb 18, 2014, at 9:37 AM, Quentin Colombet <qcolombet at apple.com> wrote:
> >>>>>> 
> >>>>>>> Hi Tom,
> >>>>>>> 
> >>>>>>> On Feb 18, 2014, at 9:21 AM, Tom Stellard <tom at stellard.net> wrote:
> >>>>>>> 
> >>>>>>>> Hi Quentin,
> >>>>>>>> 
> >>>>>>>> Sorry I missed this on the first time around: 
> >>>>>>>> 
> >>>>>>>>> --- a/lib/Transforms/Scalar/CodeGenPrepare.cpp
> >>>>>>>>> +++ b/lib/Transforms/Scalar/CodeGenPrepare.cpp
> >>>>>>>>> @@ -1728,6 +1730,35 @@
> >>>>>>>>> TypePromotionHelper::promoteOperandForOther(Instruction *SExt,
> >>>>>>>>> return SExtOpnd;
> >>>>>>>>> }
> >>>>>>>>> 
> >>>>>>>>> +/// IsPromotionProfitable - Check whether or not promoting an
> >>>>>>>>> instruction
> >>>>>>>>> +/// to a wider type was profitable.
> >>>>>>>>> +/// \p MatchedSize gives the number of instructions that have been
> >>>>>>>>> matched
> >>>>>>>>> +/// in the addressing mode after the promotion was applied.
> >>>>>>>>> +/// \p SizeWithPromotion gives the number of created instructions for
> >>>>>>>>> +/// the promotion plus the number of instructions that have been
> >>>>>>>>> +/// matched in the addressing mode before the promotion.
> >>>>>>>>> +/// \p PromotedOperand is the value that has been promoted.
> >>>>>>>>> +/// \return True if the promotion is profitable, false otherwise.
> >>>>>>>>> +bool
> >>>>>>>>> +AddressingModeMatcher::IsPromotionProfitable(unsigned MatchedSize,
> >>>>>>>>> +                                             unsigned SizeWithPromotion,
> >>>>>>>>> +                                             Value *PromotedOperand) const {
> >>>>>>>>> +  // We folded less instructions than what we created to promote the operand.
> >>>>>>>>> +  // This is not profitable.
> >>>>>>>>> +  if (MatchedSize < SizeWithPromotion)
> >>>>>>>>> +    return false;
> >>>>>>>>> +  if (MatchedSize > SizeWithPromotion)
> >>>>>>>>> +    return true;
> >>>>>>>>> +  // The promotion is neutral but it may help folding the signextension in
> >>>>>>>>> +  // loads for instance.
> >>>>>>>>> +  // Check that we did not create an illegal instruction.
> >>>>>>>>> +  Instruction *PromotedInst = dyn_cast<Instruction>(PromotedOperand);
> >>>>>>>>> +  if (!PromotedInst)
> >>>>>>>>> +    return false;
> >>>>>>>>> +  return TLI.isOperationLegalOrCustom(PromotedInst->getOpcode(),
> >>>>>>>>> +                                      EVT::getEVT(PromotedInst->getType()));
> >>>>>>>> 
> >>>>>>>> This won't work, because the IR Instructions and SelectionDAG Opcodes
> >>>>>>>> have different enumeration values.
> >>>>>>> Right, good catch!
> >>>>>>> 
> >>>>>>>> The original test case must have
> >>>>>>>> passed, because it is using a default TargetLowering implementation
> >>>>>>>> rather than the one from R600.
> >>>>>>>> 
> >>>>>>>> I've attached an updated version of the original test case which compiles
> >>>>>>>> the program using llc and triggers the bug again.
> >>>>>>>> 
> >>>>>>>> I couldn't find other transforms that use the isOperation* callbacks, so
> >>>>>>>> I think you may have to add a function to convert from IR Instruction to
> >>>>>>>> SelectionDAG Opcodes or implement this some other way.
> >>>>>>> I think a specific hook in TargetLowering may be the best approach here.
> >>>>>>> Let me see what I can come up with.
> >>>>>>> If you have ideas on the naming, let me know :).
> >>>>>> In fact, we may be able to use this:
> >>>>>> int TargetLoweringBase::InstructionOpcodeToISD(unsigned Opcode)const
> >>>>> 
> >>>>> Oh, I didn't see that.  That should work.
> >>>> Almost there.
> >>>> I am seeing a link error when creating the bugpoint executable.
> >>>> 
> >>>> llvm[2]: Linking Release executable bugpoint (without symbols)
> >>>> Undefined symbols for architecture x86_64:
> >>>> "llvm::TargetLoweringBase::InstructionOpcodeToISD(unsigned int) const", referenced from:
> >>>>     (anonymous namespace)::AddressingModeMatcher::MatchOperationAddr(llvm::User*, unsigned int, unsigned int, bool*) in libLLVMScalarOpts.a(CodeGenPrepare.o)
> >>>> ld: symbol(s) not found for architecture x86_64
> >>>> 
> >>>> The thing that I do not understand is why the linker is not find this function, whereas it does not complain about TargetLoweringBase::isLegalAddressingMode.
> >>>> I may have missed something obvious, but I do not see it.
> >>> 
> >>> I'm not seeing this error on my machine.  What build system are you
> >>> using?
> >> Makefile on Mac OS.
> >> 
> >>> Did you try running make clean first?
> >> I’ve tried but it does not seem to make the trick.
> >> 
> >> Could you try the attached patch?
> >> 
> > 
> > I've tested this and it builds fine for me on Linux with autoconf
> > and it also fixes the testcase.
> > 
> > -Tom
> > 
> >> Thanks,
> >> -Quentin
> >> 
> >>> 
> >>> -Tom
> >>> 
> >>>> 
> >>>> Any idea?
> >>>> 
> >>>> Thanks,
> >>>> -Quentin
> >>>>> 
> >>>>> -Tom
> >>>>>> 
> >>>>>>> 
> >>>>>>> Cheers,
> >>>>>>> Quentin
> >>>>>>>> 
> >>>>>>>> Thanks,
> >>>>>>>> Tom
> >>>>>>>> <update-cgp-test.case.diff>
> >>>>>>> 
> >>>>>>> _______________________________________________
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> >>>>>>> llvm-commits at cs.uiuc.edu
> >>>>>>> http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
> 