https://gcc.gnu.org/bugzilla/show_bug.cgi?id=31485
--- Comment #20 from Joel Yliluoma <bisqwit at iki dot fi> --- (In reply to Jakub Jelinek from comment #16) > (In reply to Joel Yliluoma from comment #15) > > (In reply to Richard Biener from comment #14) > > > I also think llvms code generation is bogus since it appears the ABI > > > does not guarantee zeroed upper elements of the xmm0 argument > > > which means they could contain sNaNs: > > > > Why would it matter that the unused portions of the register contain NaNs? > > Because it could then raise exceptions that shouldn't be raised? Which exceptions would be generated by data in an unused portion of a register? Does for example “addps” generate an exception if one or two of the operands contains NaNs? Which instructions would generate exceptions? I can only think of divps, when dividing by a zero, but it does not seem that even LLVM compiles the two-element vector division into divps. If the register is passed as a parameter to a library function, they would not make judgments based on the values of the unused portions of the registers.
