On Mon, 19 Aug 2019, Tejas Joshi wrote: > How can I add a target hook to specify the FP_INT_* values from libm ?
See target.def. You'll need a GCC-specific enum (GCC_FP_INT_*, say) that GCC uses internally, and a hook that maps between that and FP_INT_*. I'm guessing that for the likely uses, maybe the hook should map from FP_INT_* to GCC_FP_INT_* (so it gets used on constant arguments to the built-in function to say which rounding direction they are in GCC's internal enum). It will need to be able to return that a constant doesn't map to a known rounding mode (not an error, just means that call can't be expanded inline or optimized to a constant). Then the relevant macro giving the default for glibc systems should be defined in config/gnu-user.h (see how it defines e.g. TARGET_LIBC_HAS_FUNCTION). > Also as this includes rounding to integers, does it involve any RTL > related complications that we have encountered in FADD ? The new RTL would effectively be variants of the fix_trunc and fixuns_trunc patterns, which can use (fix) and (unsigned_fix) RTL; the new variants would take an argument in a floating-point mode, returning one in an integer mode - but with extra information involved about the number of bits, rounding direction, handling of "inexact". fix_trunc and fixuns_trunc / (fix) and (unsigned_fix) always use FP_INT_TOWARDZERO, always use the width of the mode and have unspecified "inexact" handling for non-integer in-range values (they correspond to C casts) so are not themselves suitable for implementing the new built-in functions (but the particular instructions those patterns expand to are likely to be suitable for certain arguments to certain of the new built-in functions). -- Joseph S. Myers jos...@codesourcery.com
