Hi, Jim On Mon, Feb 22, 2016 at 12:53 PM, Jim Wilson <jim.wil...@linaro.org> wrote: > On Mon, Feb 22, 2016 at 7:55 AM, David Edelsohn <dje....@gmail.com> wrote: >> If I remove extendqihi2 (extend:HI pattern) from the PowerPC port, >> will that cause any problems for the GCC RTL type system or inhibit >> optimizations? I see that Alpha and SPARC define extendqihi2, but >> IA-64 and AArch64 do not, so there is precedent for both approaches. > > aarch64 does have an extendqihi2 pattern. It uses so many iterator > macros that you can't use grep to look for stuff. The extendqihi2 > pattern is called <ANY_OPTAB>qihi2.\
Thanks for the response. I had missed the all-encompassing iterator for qidi2. > If you have a target with registers larger than HImode, no HImode > register operations, qi/hi loads set the entire register, and you > define PROMOTE_MODE to convert all QImode and HImode operations to the > same larger mode with the same signedness, then I don't think that > there is any advantage to having an extendqihi2 pattern. You should > get the same code with or without it, as a qimode to himode conversion > is a no-op. The only difference should be that with an extendqihi2 > pattern you will see some HImode operations in the RTL, without > extendqihi2 you will see equivalent operations in the promoted mode. > > If you are concerned about this, then just try compiling some large > code base using two compilers, one with extendqihi2 and one without, > and check to see if there are any code generation differences. Segher did a quick sniff test on a large code base and found two minor differences in code generation. I wanted to check if there was any more information than anecdotes. Thanks, David
