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RE: [RFC v2] MIPS ABI Extension for IEEE Std 754 Non-Compliant Interlinking
- From: Joseph Myers <joseph at codesourcery dot com>
- To: "Maciej W. Rozycki" <macro at imgtec dot com>
- Cc: Matthew Fortune <Matthew dot Fortune at imgtec dot com>, "linux-mips at linux-mips dot org" <linux-mips at linux-mips dot org>, "libc-alpha at sourceware dot org" <libc-alpha at sourceware dot org>, "binutils at sourceware dot org" <binutils at sourceware dot org>, "gcc at gcc dot gnu dot org" <gcc at gcc dot gnu dot org>
- Date: Mon, 25 Jul 2016 15:49:07 +0000
- Subject: RE: [RFC v2] MIPS ABI Extension for IEEE Std 754 Non-Compliant Interlinking
- Authentication-results: sourceware.org; auth=none
- References: <alpine.DEB.2.00.1605141043120.6794@tp.orcam.me.uk> <6D39441BF12EF246A7ABCE6654B023537E40C27F@hhmail02.hh.imgtec.org> <alpine.DEB.2.00.1607121323050.4076@tp.orcam.me.uk>
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
joseph@codesourcery.com