On 8/29/22 15:54, Jakub Jelinek via Gcc-patches wrote:
On Mon, Aug 29, 2022 at 03:45:33PM +0200, Aldy Hernandez wrote:
For convenience, singleton_p() returns false for a NAN. IMO, it makes the implementation cleaner, but I'm not wed to the idea if someone objects.If singleton_p() is used to decide whether one can just replace a variable with singleton range with a constant, then certainly. If MODE_HAS_SIGNED_ZEROS, zero has 2 representations (-0.0 and 0.0) and NaNs have lots of different representations (the sign bit is ignored except for stuff like copysign/signbit, there are qNaNs and sNaNs and except for the single case how Inf is represented, all other values of the mantissa mean different representations of NaN). So, unless we track which exact form of NaN can appear, NaN or any [x, x] range with NaN property set can't be a singleton. There could be programs that propagate something important in NaN mantissa and would be upset if frange kills that. Of course, one needs to take into account that when a FPU creates NaN, it will create the canonical qNaN. Jakub
But the NaNs are irrelevant with -ffinite-math-only, as are the various Infs (I do not know offhand which MODE_ that is) ...
Kind regards, -- Toon Moene - e-mail: t...@moene.org - phone: +31 346 214290 Saturnushof 14, 3738 XG Maartensdijk, The Netherlands
