optimizer discards sign information

[LIU Hao]

在 2024-04-10 17:52, Xi Ruoyao via Gcc-help 写道:
> No, the OP is still thinking it's a wrong-code.

Would you read the Subject please?


     u32 x = a * b;
     u64 r = x;
     return r;

This is same as

     u32 x = (int) a * (int) b;
     u64 r = x;
     return r;

and

     return (u64)(u32) ((int) a * (int) b);


The code requests an `int` be zero-extended to a `u64` (if the result is written to EAX then this is 
no-op), but GCC performs sign extension anyway. Do you still consider it not a bug?



-- 
Best regards,
LIU Hao

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