The R600 ISA documentation only says that the DX10 variants of MIN and MAX use DX10 handling of NaNs. It does not say anything about the non-DX10 variants.
Marek On Sun, Apr 14, 2013 at 8:16 PM, Roland Scheidegger <srol...@vmware.com>wrote: > Am 14.04.2013 18:39, schrieb Marek Olšák: > > On Sun, Apr 14, 2013 at 5:24 PM, Roland Scheidegger <srol...@vmware.com > > <mailto:srol...@vmware.com>> wrote: > > > > Am 14.04.2013 10:12, schrieb jfons...@vmware.com > > <mailto:jfons...@vmware.com>:> - TBD > > > + Start an IF ... ELSE .. ENDIF block. Condition evaluates to > > true if > > > + > > > + src0.x != 0.0 > > > + > > > + where src0.x is interpreted as a floating point register. > > Maybe should say something wrt evaluation of NaNs? I know we haven't > > really established rules for comparisons etc. wrt NaNs but those > > bools-as-float make me cry. I guess it is no different though than > other > > float opcodes, if we now really have a definition saying IF takes > _any_ > > float not just a bool-as-float which was loosely implied before. > > > > > > I don't know where the term "bool-as-float" came from, but I'd rather > > not use it unless it's properly defined somewhere, and TGSI doesn't have > > bools anyway, so why bother? The GLSL compiler or glsl-to-tgsi is > > responsible for converting bools to either floats or ints and TGSI > > shouldn't need to care. Both r300g and r600g use (src0.x != 0.0) for IF > > and (src0.x != 0) for UIF (r600-only), so there is always the > > "not-equal-to" operator, which is also well defined for NaNs. > That depends on your definition of "well defined". llvm for instance has > both "ordered not equal" and "unordered not equal" operators for > precisely this reason. But yes I guess ieee-754 has some defined > behavior there. > That "bool-as-float" essentially comes from state trackers, because the > language they are translating from require bools as "if" inputs - hence > the input value always should have been the result of some comparison > (or similar) operation (which in turn return these fake bools). > But I agree this was never really documented, so just clearly stating > you can pass in any float is just fine (it means that state trackers now > are explicitly allowed to omit the comparison for simple cases like this > one, "if(a != 0)...", well if they can detect it, it was not really > obvious without documentation before if that would be ok). So in that > sense nothing more needs to be said about NaNs, since they just adhere > to the same rules as in other places (meaning pretty much undefined for > most things, currently). > > > > > Also if you care about NaNs, we should start by defining how > > instructions should handle them, e.g. how relational operators handle > > NaNs, whether the multiplication operator follows the rule 0*anything = > > 0 (MUL, MAD, DP4, ...), etc. > > > > R600 have separate opcodes depending on what behavior you want, for > example: > > - The MUL opcode follows the rule 0*anything = 0. (DX9) > > - The MUL_IEEE opcode follows the IEEE behavior. > > > > The other opcodes with both the DX9 and IEEE behavior are: MAD, DP4, > > EX2, LG2, RCP, RSQ. There are also separate MIN and MAX opcodes for DX9 > > and DX10. We should choose our opcodes carefully depending on whether we > > are implementing a DX9, DX10, OpenGL, or OpenCL state tracker. > > Yes indeed. d3d10 has quite strict rules which are mostly ieee754 (or > ieee754r) but with some deviations. Other specs tend to be more lenient, > and requiring strict rules could add quite some overhead, so we might > want to introduce additional opcodes. How does MIN/MAX work for dx9 btw? > DX10 will require you to give back the non-NaN value if only one > argument is NaN (which seems to be ieee754r behavior), which for > instance unfortunately doesn't translate well to sse2 code (as sse2 will > just give you the second source if there's a NaN in either src which > means you had to use cmp/select instead and be careful about what > comparison you use there since the cpu doesn't support the full set of > "ordered" and "unordered" comparisons unless you've got avx though > presumably llvm would take care of that if you use the right comparison > ops there). > > Roland >
_______________________________________________ mesa-dev mailing list mesa-dev@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/mesa-dev
