[llvm] r374102 - Mark several PointerIntPair methods as lvalue-only

[Jordan Rose via llvm-commits]

I had to dig up the example again, but it was basically a nested PointerIntPair, leading to

importantFieldAndFlags.getPointer().setInt(true); // this setInt is discarded

I don't see how you could write a verifier to catch this without looking at the body of 'setInt', although maybe you could infer it from the method being named "set*".

Jordan


> On Oct 14, 2019, at 16:34, David Blaikie <dblaikie at gmail.com> wrote:
> 
> Hmm, actually, thinking about this again - what's the bug usage you're trying to fix? If these functions don't return any value, what sort of mistakes could they introduce?
> 
> It's not like someone's going to accidentally write "foo(bar().baz())" (where baz() is the mutating-not-returning function)
> 
> Is it in cases like "bar().baz()" where bar() returns by value & the author thought it returned by non-const-ref?
> 
> I don't think the warning or tidy-check should suggest adding a reference qualifier - just catching the usage that's bogus (ie: diagnosing the "bar().baz()" usage, not the definition of "baz()" itself) - because I think there's just too much API surface area to annotate everything.
> 
> On Mon, Oct 14, 2019 at 4:31 PM Jordan Rose <jordan_rose at apple.com <mailto:jordan_rose at apple.com>> wrote:
> I could see it as a clang-tidy pass. "This method modifies members of 'this' but does not return 'this' or use it in any way [after modification]; do you want to make it lvalue-only?" I wouldn't make it a full warning because lvalue qualifiers are still fairly esoteric and people may not want to add them to their codebase even if they'd catch bugs.
> 
> Jordan
> 
> 
>> On Oct 14, 2019, at 15:43, David Blaikie <dblaikie at gmail.com <mailto:dblaikie at gmail.com>> wrote:
>> 
>> Seems like a losing race to try to flag every API surface area that might have this problem.
>> 
>> Is it worth considering a clang-tidy or full clang warning for cases like this? (& could diagnose the usage directly)
>> 
>> On Tue, Oct 8, 2019 at 11:59 AM Jordan Rose via llvm-commits <llvm-commits at lists.llvm.org <mailto:llvm-commits at lists.llvm.org>> wrote:
>> Author: jrose
>> Date: Tue Oct  8 12:01:48 2019
>> New Revision: 374102
>> 
>> URL: http://llvm.org/viewvc/llvm-project?rev=374102&view=rev <http://llvm.org/viewvc/llvm-project?rev=374102&view=rev>
>> Log:
>> Mark several PointerIntPair methods as lvalue-only
>> 
>> No point in mutating 'this' if it's just going to be thrown away.
>> 
>> https://reviews.llvm.org/D63945 <https://reviews.llvm.org/D63945>
>> 
>> Modified:
>>     llvm/trunk/include/llvm/ADT/PointerIntPair.h
>> 
>> Modified: llvm/trunk/include/llvm/ADT/PointerIntPair.h
>> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/ADT/PointerIntPair.h?rev=374102&r1=374101&r2=374102&view=diff <http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/ADT/PointerIntPair.h?rev=374102&r1=374101&r2=374102&view=diff>
>> ==============================================================================
>> --- llvm/trunk/include/llvm/ADT/PointerIntPair.h (original)
>> +++ llvm/trunk/include/llvm/ADT/PointerIntPair.h Tue Oct  8 12:01:48 2019
>> @@ -13,6 +13,7 @@
>>  #ifndef LLVM_ADT_POINTERINTPAIR_H
>>  #define LLVM_ADT_POINTERINTPAIR_H
>> 
>> +#include "llvm/Support/Compiler.h"
>>  #include "llvm/Support/PointerLikeTypeTraits.h"
>>  #include "llvm/Support/type_traits.h"
>>  #include <cassert>
>> @@ -59,19 +60,19 @@ public:
>> 
>>    IntType getInt() const { return (IntType)Info::getInt(Value); }
>> 
>> -  void setPointer(PointerTy PtrVal) {
>> +  void setPointer(PointerTy PtrVal) LLVM_LVALUE_FUNCTION {
>>      Value = Info::updatePointer(Value, PtrVal);
>>    }
>> 
>> -  void setInt(IntType IntVal) {
>> +  void setInt(IntType IntVal) LLVM_LVALUE_FUNCTION {
>>      Value = Info::updateInt(Value, static_cast<intptr_t>(IntVal));
>>    }
>> 
>> -  void initWithPointer(PointerTy PtrVal) {
>> +  void initWithPointer(PointerTy PtrVal) LLVM_LVALUE_FUNCTION {
>>      Value = Info::updatePointer(0, PtrVal);
>>    }
>> 
>> -  void setPointerAndInt(PointerTy PtrVal, IntType IntVal) {
>> +  void setPointerAndInt(PointerTy PtrVal, IntType IntVal) LLVM_LVALUE_FUNCTION {
>>      Value = Info::updateInt(Info::updatePointer(0, PtrVal),
>>                              static_cast<intptr_t>(IntVal));
>>    }
>> @@ -89,7 +90,7 @@ public:
>> 
>>    void *getOpaqueValue() const { return reinterpret_cast<void *>(Value); }
>> 
>> -  void setFromOpaqueValue(void *Val) {
>> +  void setFromOpaqueValue(void *Val) LLVM_LVALUE_FUNCTION {
>>      Value = reinterpret_cast<intptr_t>(Val);
>>    }
>> 
>> 
>> 
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