Segher Boessenkool <seg...@kernel.crashing.org> writes: > On Thu, Aug 15, 2019 at 01:47:47PM +0100, Richard Sandiford wrote: >> Tejas Joshi <tejasjoshi9...@gmail.com> writes: >> > Hello. >> > I just wanted to make sure that I am looking at the correct code here. >> > Except for rtl.def where I should be introducing something like >> > float_contract (or float_narrow?) and also simplify-rtx.c, breakpoints > > I like that "float_narrow" name :-) > >> > set on functions around expr.c, cfgexpand.c where I grep for >> > float_truncate/FLOAT_TRUNCATE did not hit. >> > Also, in what manner should float_contract/narrow be different from >> > float_truncate as both are trying to do similar things? (truncation >> > from DF to SF) >> >> I think the code should instead be a fused addition and truncation, >> a bit like FMA is a fused addition and multiplication. Describing it as >> a DFmode addition followed by some conversion to SF would still involve >> double rounding. > > How so? It would *mean* there is only single rounding, even! That's > the whole point of it.
But a PLUS should behave as a PLUS in any context. Making its behaviour dependent on the containing rtxes (if any) would be a can of worms. Richard
