[LLVMdev] a constant folding case causing different results w/ot optimization

[Zheng, Bixia]

Hi,

 

The optimizer folds "(unsigned int) -1.0f" to 0. As a result, the
following routine foo returns 0 with optimization, and returns -1
(0xffffffff) without optimization.

 

unsigned int foo()

{

    float myfloat = -1.0f;

    unsigned int myint = (unsigned int) myfloat;

    return myint;

}

 

INSTCOMBINE ITERATION #0 on

IC: ConstFold to: i32 0 from:   %conv = fptoui float -1.000000e+000 to
i32      ; <i32> [#uses=1]

 

 

 

While the result of "(unsigned int) -1.0f" is probably implementation
defined, both gcc and Microsoft cl produce -1.

Will you consider this an optimizer bug and fix it?

 

Thanks,

 

bixia

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