[llvm] r323582 - [GlobalISel][Legalizer] Convert the FP constants to the right APFloat type for G_FCONSTANT.

[Amara Emerson via llvm-commits]

Hi Hans,

Can we merge this into 6.0 please.

Thanks,
Amara

> On Jan 26, 2018, at 11:07 PM, Amara Emerson via llvm-commits <llvm-commits at lists.llvm.org> wrote:
> 
> Author: aemerson
> Date: Fri Jan 26 23:07:20 2018
> New Revision: 323582
> 
> URL: http://llvm.org/viewvc/llvm-project?rev=323582&view=rev
> Log:
> [GlobalISel][Legalizer] Convert the FP constants to the right APFloat type for G_FCONSTANT.
> 
> We weren't converting the immediate ConstantFP during legalization, which caused
> the wrong bit patterns to be emitted for half type FP constants.
> 
> Fixes PR36106.
> 
> Modified:
>    llvm/trunk/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
>    llvm/trunk/test/CodeGen/AArch64/GlobalISel/legalize-constant.mir
> 
> Modified: llvm/trunk/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/GlobalISel/LegalizerHelper.cpp?rev=323582&r1=323581&r2=323582&view=diff
> ==============================================================================
> --- llvm/trunk/lib/CodeGen/GlobalISel/LegalizerHelper.cpp (original)
> +++ llvm/trunk/lib/CodeGen/GlobalISel/LegalizerHelper.cpp Fri Jan 26 23:07:20 2018
> @@ -715,7 +715,24 @@ LegalizerHelper::widenScalar(MachineInst
>   }
>   case TargetOpcode::G_FCONSTANT: {
>     unsigned DstExt = MRI.createGenericVirtualRegister(WideTy);
> -    MIRBuilder.buildFConstant(DstExt, *MI.getOperand(1).getFPImm());
> +    const ConstantFP *CFP = MI.getOperand(1).getFPImm();
> +    APFloat Val = CFP->getValueAPF();
> +    LLVMContext &Ctx = MIRBuilder.getMF().getFunction().getContext();
> +    auto LLT2Sem = [](LLT Ty) {
> +      switch (Ty.getSizeInBits()) {
> +      case 32:
> +        return &APFloat::IEEEsingle();
> +        break;
> +      case 64:
> +        return &APFloat::IEEEdouble();
> +        break;
> +      default:
> +        llvm_unreachable("Unhandled fp widen type");
> +      }
> +    };
> +    bool LosesInfo;
> +    Val.convert(*LLT2Sem(WideTy), APFloat::rmTowardZero, &LosesInfo);
> +    MIRBuilder.buildFConstant(DstExt, *ConstantFP::get(Ctx, Val));
>     MIRBuilder.buildFPTrunc(MI.getOperand(0).getReg(), DstExt);
>     MI.eraseFromParent();
>     return Legalized;
> 
> Modified: llvm/trunk/test/CodeGen/AArch64/GlobalISel/legalize-constant.mir
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/AArch64/GlobalISel/legalize-constant.mir?rev=323582&r1=323581&r2=323582&view=diff
> ==============================================================================
> --- llvm/trunk/test/CodeGen/AArch64/GlobalISel/legalize-constant.mir (original)
> +++ llvm/trunk/test/CodeGen/AArch64/GlobalISel/legalize-constant.mir Fri Jan 26 23:07:20 2018
> @@ -75,7 +75,7 @@ body: |
>     ; CHECK: %w0 = COPY [[C]](s32)
>     ; CHECK: [[C1:%[0-9]+]]:_(s64) = G_FCONSTANT double 2.000000e+00
>     ; CHECK: %x0 = COPY [[C1]](s64)
> -    ; CHECK: [[C2:%[0-9]+]]:_(s32) = G_FCONSTANT half 0xH0000
> +    ; CHECK: [[C2:%[0-9]+]]:_(s32) = G_FCONSTANT float 0.000000e+00
>     ; CHECK: [[FPTRUNC:%[0-9]+]]:_(s16) = G_FPTRUNC [[C2]](s32)
>     ; CHECK: [[ANYEXT:%[0-9]+]]:_(s32) = G_ANYEXT [[FPTRUNC]](s16)
>     ; CHECK: %w0 = COPY [[ANYEXT]](s32)
> 
> 
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