[llvm] r292753 - [IR] Use const_cast to reuse the const version of two BasicBlock methods that are duplicated for both const and non-const. NFC

[Craig Topper via llvm-commits]

Why would const_casting the Module * result in your formulation not also be
a problem?

~Craig

On Mon, Jan 23, 2017 at 9:36 AM, David Blaikie <dblaikie at gmail.com> wrote:

>
>
> On Sat, Jan 21, 2017 at 11:04 PM Craig Topper via llvm-commits <
> llvm-commits at lists.llvm.org> wrote:
>
>> Author: ctopper
>> Date: Sun Jan 22 00:53:04 2017
>> New Revision: 292753
>>
>> URL: http://llvm.org/viewvc/llvm-project?rev=292753&view=rev
>> Log:
>> [IR] Use const_cast to reuse the const version of two BasicBlock methods
>> that are duplicated for both const and non-const. NFC
>>
>> Similar is already done for other methods in BasicBlock.
>>
>> Modified:
>>     llvm/trunk/include/llvm/IR/BasicBlock.h
>>     llvm/trunk/lib/IR/BasicBlock.cpp
>>
>> Modified: llvm/trunk/include/llvm/IR/BasicBlock.h
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/
>> llvm/IR/BasicBlock.h?rev=292753&r1=292752&r2=292753&view=diff
>> ============================================================
>> ==================
>> --- llvm/trunk/include/llvm/IR/BasicBlock.h (original)
>> +++ llvm/trunk/include/llvm/IR/BasicBlock.h Sun Jan 22 00:53:04 2017
>> @@ -104,13 +104,17 @@ public:
>>    /// or nullptr it the function does not have a module.
>>    ///
>>    /// Note: this is undefined behavior if the block does not have a
>> parent.
>> -  const Module *getModule() const;
>>    Module *getModule();
>> +  const Module *getModule() const {
>> +    return const_cast<BasicBlock *>(this)->getModule();
>>
>
> I think this is technically UB if the BasicBlock were actually const
> (though I suppose we don't have any of those)
>
> But the opposite formulation - implementing the non-const version in terms
> of the const one, doesn't have that problem:
>
>   Module *getModule() {
>     return const_cast<Module*>(implicit_cast<const
> BasicBlock*>(this)->getModule());
>   }
>
> (I don't think we have an implicit_cast template - we could add one, but
> don't necessarily have to for this example/case)
>
>
>> +  }
>>
>>    /// \brief Returns the terminator instruction if the block is well
>> formed or
>>    /// null if the block is not well formed.
>>    TerminatorInst *getTerminator();
>> -  const TerminatorInst *getTerminator() const;
>> +  const TerminatorInst *getTerminator() const {
>> +    return const_cast<BasicBlock *>(this)->getTerminator();
>> +  }
>>
>>    /// \brief Returns the call instruction calling
>> @llvm.experimental.deoptimize
>>    /// prior to the terminating return instruction of this basic block,
>> if such a
>>
>> Modified: llvm/trunk/lib/IR/BasicBlock.cpp
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/IR/
>> BasicBlock.cpp?rev=292753&r1=292752&r2=292753&view=diff
>> ============================================================
>> ==================
>> --- llvm/trunk/lib/IR/BasicBlock.cpp (original)
>> +++ llvm/trunk/lib/IR/BasicBlock.cpp Sun Jan 22 00:53:04 2017
>> @@ -113,10 +113,6 @@ void BasicBlock::moveAfter(BasicBlock *M
>>        getIterator());
>>  }
>>
>> -const Module *BasicBlock::getModule() const {
>> -  return getParent()->getParent();
>> -}
>> -
>>  Module *BasicBlock::getModule() {
>>    return getParent()->getParent();
>>  }
>> @@ -125,11 +121,6 @@ TerminatorInst *BasicBlock::getTerminato
>>    if (InstList.empty()) return nullptr;
>>    return dyn_cast<TerminatorInst>(&InstList.back());
>>  }
>> -
>> -const TerminatorInst *BasicBlock::getTerminator() const {
>> -  if (InstList.empty()) return nullptr;
>> -  return dyn_cast<TerminatorInst>(&InstList.back());
>> -}
>>
>>  CallInst *BasicBlock::getTerminatingMustTailCall() {
>>    if (InstList.empty())
>>
>>
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>
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