> The RTL needs to be something that > does *not* match the combination of separate operations (just as fma has > its own RTL, and a separate pass is responsible for converting separate
So do I need to introduce fadd's own RTL just as fma which would emit a fused instruction while -ffp-contract is default (fast) and would emit separate instructions like add in DFmode and then truncate to SF? while -ffp-contract=off ? (just as fma) On Tue, 13 Aug 2019 at 03:22, Segher Boessenkool <seg...@kernel.crashing.org> wrote: > > On Mon, Aug 12, 2019 at 09:20:18PM +0000, Joseph Myers wrote: > > On Mon, 12 Aug 2019, Segher Boessenkool wrote: > > > > > (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"))))] > > > > That sort of pattern is incorrect for a fused operation such as fadd, > > because combine could match it for code that is supposed to do separate > > addition and narrowing conversion. The RTL needs to be something that > > does *not* match the combination of separate operations (just as fma has > > its own RTL, and a separate pass is responsible for converting separate > > operations to fused ones in the -ffp-contract=fast case where it's > > permitted). > > Ugh, we allow disabling contraction, I forgot. Rats. > > > Segher
