[cfe-dev] Fwd: Library calls for complex types and terminate scopes.

[John McCall via cfe-dev]

On Tue, Nov 17, 2015 at 4:54 PM, Reid Kleckner <rnk at google.com> wrote:

> Maybe you could mark the runtime function nounwind when you get its
> declaration here:
>   llvm::Constant *Func = CGF.CGM.CreateBuiltinFunction(FTy, LibCallName
> /*pass an AttributeSet here*/);
>
> Then you won't have to call setDoesNotThrow() later.
>

The by-design way to do this is to add a noexcept specification to the
ExtInfo being passed to arrangeFreeFunctionCall.

John.


> On Tue, Nov 17, 2015 at 4:43 PM, Samuel F Antao via cfe-dev <
> cfe-dev at lists.llvm.org> wrote:
>
>> Hi all,
>>
>> I came across an issue that happens to trigger an assertion in clang if
>> an operation with type type is implemented in a scope that happens to
>> install a terminate scope in the exceptions stack. I see the issue while
>> using complex arithmetic in OpenMP regions, but I believe that could also
>> be a problem for non-openMP codes.
>>
>> The problem happens in `ComplexExprEmitter::EmitComplexBinOpLibCall` and
>> is caused by an assertion in:
>>
>> ```
>>   RValue Res = CGF.EmitCall(FuncInfo, Func, ReturnValueSlot(), Args,
>>                             nullptr, &Call);
>>   cast<llvm::CallInst>(Call)->setCallingConv(CGF.CGM.getBuiltinCC());
>>   cast<llvm::CallInst>(Call)->setDoesNotThrow();
>> ```
>>
>> `EHStack.requiresLandingPad()` is used by `EmitCall` and is true if we
>> have a scope installed in the exceptions stack. This causes `EmitCall` to
>> produce an invoke instruction instead of a call instruction.
>>
>> One of the ways to tackle the issue is use the proper attributes for the
>> library function (e.g. no unwind). Is this the right thing to do? Or can
>> these library calls throw in some cases?
>>
>> Any thoughts?
>>
>> Here is a simple code that replicates the problem:
>> ```
>> int main (int argc, char *argv[]){
>>   double _Complex dc = (double)argc + 3*I;
>>
>>   dc *= dc;
>>   #pragma omp parallel
>>   {
>>     dc *= dc;
>>   }
>>   printf("%lf %lf\n",creal(dc),cimag(dc));
>>   return 0;
>> }
>> ```
>>
>> Thanks!
>> Samuel
>>
>>
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>> cfe-dev at lists.llvm.org
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>>
>>
>


-- 
I suppose you'd like my real thoughts as well.
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