Bug 20557 - bogus cpu parameter crashes llc

[iid_iunknown]

Summary

Hi Hao,

Would you be able to find some time and review this simple correction that we discussed previously, please?
Thank you.

Problem summary:

Regression caused by http://reviews.llvm.org/D4322.
Llc crashes when compiling the attached file if -march=aarch64 and -mcpu specifies a cpu that is invalid for this architecture.

The problem is with v1f32 type. According to AArch64TargetLowering::getPreferredVectorAction this vector type should be widened on aarch64.

If a bogus CPU is passed to llc, v2f32 is not added to the legal types list.
Because of that, v1f32 fails to be widened, so TargetLoweringBase::computeRegisterProperties() falls through to the next switch-case branch, which sets the preferred type action to TypeSplitVector. This means we are trying to split one element vector. This triggers the assert in VectorType::get. The same applies to other 1-sized vector types listed in getPreferredVectorAction: v1i8, v1i16 and v1i32.

Fix summary:

If the preferred action for a one element vector is neither TypeSplitVector nor TypeScalarizeVector and it fails to be applied, then the action is set to TypeScalarizeVector instead of TypeSplitVector.

[• HaoLiu]

Hi Oleg,

I'm very sorry that I missed this message for such a long time.

I think your solution is reasonable. But it looks somehow misleading. People don't know what is the current PreferredAction. So I think we'd better use more if and else as following:

if (PreferredAction == TypeSplitVector)
  setTypeAction TypeSplitVector 
else if (PreferredAction == TypeScalarizeVector)
   setTypeAction TypeScalarizeVector 
else
   // when the preferred action is neither TypeSplitVector nor TypeScalarizeVector
  NElts == 1 ? TypeScalarizeVector : TypeSplitVector

I just think this is more clear.

Thanks,
-Hao

[• HaoLiu]

Committed in http://llvm.org/viewvc/llvm-project?view=revision&revision=220946.
Thanks Oleg.

Thanks,
-Hao

[• HaoLiu]

Sorry, above is an incorrect link. Committed in http://llvm.org/viewvc/llvm-project?view=revision&revision=220945.

lib/CodeGen/TargetLoweringBase.cpp

case TypeScalarizeVector: {
       NumRegistersForVT[i] = getVectorTypeBreakdownMVT(VT, IntermediateVT,
           NumIntermediates, RegisterVT, this);
       RegisterTypeForVT[i] = RegisterVT;
 
       MVT NVT = VT.getPow2VectorType();
       if (NVT == VT) {
         // Type is already a power of 2.  The default action is to split.
         TransformToType[i] = MVT::Other;
-        if (PreferredAction == TypeScalarizeVector)
+        if (   PreferredAction == TypeScalarizeVector
+            || VT.getVectorNumElements() == 1)
+        {
           ValueTypeActions.setTypeAction(VT, TypeScalarizeVector);
+        }
         else
           ValueTypeActions.setTypeAction(VT, TypeSplitVector);
       } else {
         TransformToType[i] = NVT;
         ValueTypeActions.setTypeAction(VT, TypeWidenVector);
       }
       break;
     }