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Hi Joerg, > IMO if constant folding of transcendental functions makes a significant difference for your program, you likely are doing something strange already. Alas it's not as simple as that. Currently, if you declare: std::uniform_real_distribution<float> x; LLVM emits two calls to logl() with constant arguments, a fdiv and a fptoui. Libc++'s implementation is consumed and folded much more nicely by LLVM, but at the moment anyone comparing LLVM and GCC will think that GCC is around 40% better for some workloads. James On Mon,...

...m.org> wrote: > > Hi Joerg, > > > IMO if constant folding of transcendental functions makes a significant > difference for your program, you likely are doing something strange > already. > > Alas it's not as simple as that. Currently, if you declare: > > std::uniform_real_distribution<float> x; > > LLVM emits two calls to logl() with constant arguments, a fdiv and a > fptoui. > > Libc++'s implementation is consumed and folded much more nicely by LLVM, > but at the moment anyone comparing LLVM and GCC will think that GCC is > around 40% better fo...

Hi, Clang is currently unable to constant fold calls to math.h functions such as logl(), expl() etc. The problem is that APFloat doesn't have these functions, so Clang is forced to rely on the host math library. Because long double isn't portable, we only ever query the host math library for double or float results. I can see three methods for allowing constant folding for types that