[llvm] r361912 - [X86] Use 'llvm_unreachable' instead of nullptr in unreachable code to

[David Blaikie via llvm-commits]

On Tue, May 28, 2019 at 7:17 PM Pengfei Wang via llvm-commits <
llvm-commits at lists.llvm.org> wrote:

> Author: pengfei
> Date: Tue May 28 19:20:37 2019
> New Revision: 361912
>
> URL: http://llvm.org/viewvc/llvm-project?rev=361912&view=rev
> Log:
> [X86] Use 'llvm_unreachable' instead of nullptr in unreachable code to
> avoid static check fail
>
> RegClassOrBank is an object of RegClassOrRegBank, which is defined as
> using llvm::RegClassOrRegBank = typedef PointerUnion<const
> TargetRegisterClass *, const RegisterBank *>
> so control flow can not get here. Use ""llvm_unreachable" here to avoid
> "null pointer" confusion.
>
> Patch by Shengchen Kan (skan)
>
> Differential Revision: https://reviews.llvm.org/D62006
>
> Signed-off-by: pengfei <pengfei.wang at intel.com>
>
> Modified:
>     llvm/trunk/lib/CodeGen/GlobalISel/RegisterBankInfo.cpp
>     llvm/trunk/lib/Target/X86/X86InstructionSelector.cpp
>
> Modified: llvm/trunk/lib/CodeGen/GlobalISel/RegisterBankInfo.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/GlobalISel/RegisterBankInfo.cpp?rev=361912&r1=361911&r2=361912&view=diff
>
> ==============================================================================
> --- llvm/trunk/lib/CodeGen/GlobalISel/RegisterBankInfo.cpp (original)
> +++ llvm/trunk/lib/CodeGen/GlobalISel/RegisterBankInfo.cpp Tue May 28
> 19:20:37 2019
> @@ -91,7 +91,9 @@ RegisterBankInfo::getRegBank(unsigned Re
>      return RB;
>    if (auto *RC = RegClassOrBank.dyn_cast<const TargetRegisterClass *>())
>      return &getRegBankFromRegClass(*RC);
> -  return nullptr;
> +
> +  llvm_unreachable("RegClassOrBank is either a const RegisterBank* or "
> +                   "a const TargetRegisterClass*");
>

Could simplify this ^ further to:

return &getRegBankFromRegClass(*RegClassOrBank.get<const
TargetRegisterClass*>());

(since the 'get' will assert the same way the unreachable would've - though
if you prefer the more specific message you can provide with the
unreachable, that's OK too)

 }
>
>  const TargetRegisterClass &
>
> Modified: llvm/trunk/lib/Target/X86/X86InstructionSelector.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86InstructionSelector.cpp?rev=361912&r1=361911&r2=361912&view=diff
>
> ==============================================================================
> --- llvm/trunk/lib/Target/X86/X86InstructionSelector.cpp (original)
> +++ llvm/trunk/lib/Target/X86/X86InstructionSelector.cpp Tue May 28
> 19:20:37 2019
> @@ -1610,8 +1610,8 @@ bool X86InstructionSelector::selectDivRe
>    assert(RegTy == MRI.getType(Op1Reg) && RegTy == MRI.getType(Op2Reg) &&
>           "Arguments and return value types must match");
>
> -  const RegisterBank *RegRB = RBI.getRegBank(DstReg, MRI, TRI);
> -  if (!RegRB || RegRB->getID() != X86::GPRRegBankID)
> +  const RegisterBank &RegRB = *RBI.getRegBank(DstReg, MRI, TRI);
> +  if (RegRB.getID() != X86::GPRRegBankID)
>      return false;
>
>    const static unsigned NumTypes = 4; // i8, i16, i32, i64
> @@ -1709,7 +1709,7 @@ bool X86InstructionSelector::selectDivRe
>    const DivRemEntry &TypeEntry = *OpEntryIt;
>    const DivRemEntry::DivRemResult &OpEntry =
> TypeEntry.ResultTable[OpIndex];
>
> -  const TargetRegisterClass *RegRC = getRegClass(RegTy, *RegRB);
> +  const TargetRegisterClass *RegRC = getRegClass(RegTy, RegRB);
>    if (!RBI.constrainGenericRegister(Op1Reg, *RegRC, MRI) ||
>        !RBI.constrainGenericRegister(Op2Reg, *RegRC, MRI) ||
>        !RBI.constrainGenericRegister(DstReg, *RegRC, MRI)) {
>
>
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