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RE: [RFC v2] MIPS ABI Extension for IEEE Std 754 Non-Compliant Interlinking

On Thu, 14 Jul 2016, Maciej W. Rozycki wrote:

> 2. An idea has been proposed to have objects marked by the assembler to 
>    indicate whether they include an FP hardware instruction or not.  The 
>    latters would automatically become don't-cares as far as NaN encoding
>    is concerned and if all the objects were such in a given static link, 

I don't think presence of FP hardware instructions is much of a guide to 
whether code cares about NaN encodings.  I'd expect most code simply doing 
arithmetic not to care (that is, the same object code would work correctly 
on systems with either NaN encoding - given the right encodings for that 
system as inputs, it would produce the right encodings as outputs), while 
code using a NaN encoding explicitly (typically through __builtin_nan or 
folded 0.0 / 0.0 in a static initializer) cares even if that object does 
not use FP instructions.  (Formally, of course code knowing the ABI can 
creating encodings directly, implement issignaling itself, etc., but that 
should be rare.)

Joseph S. Myers

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