Why there is no unary operator in LLVM?

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#1

Hi llvmdev,

I’ve noticed that there is no unary operator in LLVM. For unary operator such as Neg or Or operator, the IR builder just creates a binary operation with one dummy operand,

[01823](http://llvm.org/doxygen/classllvm_1_1BinaryOperator.html#a073c092ce74a122e898e435e60e84599) [BinaryOperator](http://llvm.org/doxygen/classllvm_1_1BinaryOperator.html) *[BinaryOperator::CreateNeg](http://llvm.org/doxygen/classllvm_1_1BinaryOperator.html#a073c092ce74a122e898e435e60e84599)([Value](http://llvm.org/doxygen/classllvm_1_1Value.html) *Op, const [Twine](http://llvm.org/doxygen/classllvm_1_1Twine.html) &Name,
01824                                           [BasicBlock](http://llvm.org/doxygen/classllvm_1_1BasicBlock.html) *InsertAtEnd) {
01825   [Value](http://llvm.org/doxygen/classllvm_1_1Value.html) *zero = [ConstantFP::getZeroValueForNegation](http://llvm.org/doxygen/classllvm_1_1ConstantFP.html#ab4d218c572245abd0b1c895d603cba36)(Op->[getType](http://llvm.org/doxygen/classllvm_1_1Value.html#a0cf3748dba54f931bb1241ae4adc76bc)());
01826   return new [BinaryOperator](http://llvm.org/doxygen/classllvm_1_1BinaryOperator.html#acf242c32d995c5276931f545aa2bdd9c)(Instruction::Sub,
01827                             zero, Op,
01828                             Op->[getType](http://llvm.org/doxygen/classllvm_1_1Value.html#a0cf3748dba54f931bb1241ae4adc76bc)(), [Name](http://llvm.org/doxygen/classllvm_1_1BinaryOperator.html#a274586caf47dcc28ed878ad21af28152), InsertAtEnd);

However, I think it’s more natural to describe this as unary operation, and may bring benefits to the optimiser and code generator.

Can anyone tell me the reason?

Thanks!

#2

We describe it as a binary operation simply to reduce the number of
instructions in the IR. There are helper functions for things which
are really looking for unary not etc.

-Eli