[cfe-dev] Why does ABI on amd64 require bit extension of function arguments smaller than 32 bits?

[Joerg Sonnenberger via cfe-dev]

On Fri, Nov 04, 2016 at 03:58:06PM -0700, Yuri via cfe-dev wrote:
> I noticed that clang adds signext or zeroext attribute to all such function
> arguments. Why is this required? Isn't bit extension by the callee only when
> needed more efficient?

The calle is required to do the expansion. The attributes just reflect
what the content is the registers are supposed to be.

Joerg