On Wed, Aug 14, 2019 at 04:10:56PM +0000, Joseph Myers wrote: > On Wed, 14 Aug 2019, Segher Boessenkool wrote: > > > I think you can do one RTL code that replaces float_truncate in > > > > > > > > (define_insn "add_truncdfsf3" > > > > > > [(set (match_operand:SF 0 "gpc_reg_operand" "=f,wa") > > > > > > (float_truncate:SF > > > > > > (plus:DF (match_operand:DF 1 "gpc_reg_operand" "%d,wa") > > > > > > (match_operand:DF 2 "gpc_reg_operand" "d,wa"))))] > > > > but that is only meant for such explicit contraction. This can then > > happily be used to implement all such patterns. Is there some issue > > with that I overlook? > > Yes, I think such a separate RTL code would work (as would an > architecture-specific UNSPEC) - it just needs to avoid the pattern > matching RTL that can arise other than from the built-in functions. > > (Everything to do with needing -fno-math-errno to expand into such > instructions should be handled in the architecture-independent compiler.)
Does something like float d; double a, b, x; ... d = fadd (a + x, b - x); work as wanted, with such a representation? It would simplify (does it?) to d = fadd (a, b); but is that allowed? Segher
