[LLVMdev] promotion of return value.

Rafael Espindola espindola at google.com
Wed Apr 1 01:14:10 PDT 2009

> I still don't think llvm needs to do this.  We had the discussion on
> http://groups.google.com/group/ia32-abi/browse_thread/thread/f47e0106b21d9269
> The conclusion:
> ---
> I think callers need to assume that return value is in %al and that
> the upper bits of %eax are undefined.  If the caller needs a 32-bit
> sign- or zero-extended value, it needs to do the extend itself.  I
> believe GCC, ICC, and MSVC all behave this way.
> Given that, it shouldn't matter how the callee handles the upper
> bits.  It should do whatever is most convenient.

Exactly. Note that y returns a short, and z  wants an int. It is
z's responsibility to do a sign extension. The example claims that a
sign extension is not necessary.

> ---
> Andrew.
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Rafael Avila de Espindola

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