Integer promotion for register based arguments

[Andrew Haley]

On 07/25/2012 12:15 PM, Jon Beniston wrote:
> For MIPS and LM32, truncation is performed in the calling function
> and sign extension in the called function. One of these operations
> seems redundant.  For ARM, truncation is performed in the caller,
> but sign-extension isn't performed in the callee, which seems more
> efficient. Why might this be?

This is defined by the system ABI, which specifies when zero- or sign-
extension get done.  The ARM ABI explicitly requires a caller to
extend types appropriately before they are passed, and a callee can
depend on that.  We in GCC have to follow the rules, and we can take
advantage of them.

I suspect the answer to your question will be found in the ABIs of
the MIPS and LM32, but I'm not familiar with either of those.

Andrew.