[llvm] r239497 - change assert that will never fire to llvm_unreachable

[Sanjay Patel]

Thanks, David. I suppose a better fix here would be to remove the final
'else' and make this an assert again...just with an assertion predicate
that actually checks what we want:
assert(Prev != nullptr && "Unknown pattern for machine combiner");

On Thu, Jun 11, 2015 at 11:21 AM, David Blaikie <dblaikie at gmail.com> wrote:

>
>
> On Wed, Jun 10, 2015 at 4:27 PM, Sanjay Patel <spatel at rotateright.com>
> wrote:
>
>> Author: spatel
>> Date: Wed Jun 10 18:27:33 2015
>> New Revision: 239497
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=239497&view=rev
>> Log:
>> change assert that will never fire to llvm_unreachable
>>
>> Modified:
>>     llvm/trunk/lib/Target/X86/X86InstrInfo.cpp
>>
>> Modified: llvm/trunk/lib/Target/X86/X86InstrInfo.cpp
>> URL:
>> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/X86/X86InstrInfo.cpp?rev=239497&r1=239496&r2=239497&view=diff
>>
>> ==============================================================================
>> --- llvm/trunk/lib/Target/X86/X86InstrInfo.cpp (original)
>> +++ llvm/trunk/lib/Target/X86/X86InstrInfo.cpp Wed Jun 10 18:27:33 2015
>> @@ -6424,7 +6424,7 @@ void X86InstrInfo::genAlternativeCodeSeq
>>             Pattern == MachineCombinerPattern::MC_REASSOC_XA_YB)
>>      Prev = MRI.getUniqueVRegDef(Root.getOperand(2).getReg());
>>    else
>> -    assert("Unknown pattern for machine combiner");
>> +    llvm_unreachable("Unknown pattern for machine combiner");
>>
>
> Generally we try not to "branch to unreachable" & instead assert whatever
> the inverse of the branch condition was, so in this case:
>
> if (AX_BY || XA_BY)
>   ...
> else {
>   assert(AX_YB || XA_YB);
>   ...
> }
>
> But sometimes it easier to read as an if/else if/else if/else
> if/else-unreachable chain... *shrug*
>
>
>>
>>    reassociateOps(Root, *Prev, Pattern, InsInstrs, DelInstrs,
>> InstIdxForVirtReg);
>>    return;
>>
>>
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>
>
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