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Type:
Enhancement
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Resolution: Implemented
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Priority:
Medium
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Code Generation Tools
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CODEGEN-7364
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default
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None automatic. The customer did the transformation by hand to compensate.
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The compiler didn't do return-value optimisation (copy elision) in cases like the classic two-operand operator+(). The effect is an extra copy and an extra temporary variable.
The attached test case files create a class that contains floating point arrays, and does addition and subtraction operations on those arrays. When results are returns from the add and subtract operations, they are copied from a local to the result location. Instead, the result location should be directly operated on.
To build ...
% cl6x -@options.txt --symdebug:none -s main.cpp matrix2.cpp
Inspect the resulting assembly files. For the add operation in matrix2.asm, this compiler generated comment appears ...
;** 639 ----------------------- (*$P$T0).alloc = *(struct Matrix3x3::_Alloc *)&result; // [3]
This is the copy which should be avoided.
