2888 – [PATCH] speedup for float * 2.0

DMD generates slow code in simple situations such as:
double foo(double x) { return x*2; }
It creates a floating-point constant 2.0, and then generates an FMUL to multiply by it. It's particularly slow in the 80-bit real case, where two instructions (FLD and FMULP) are required.
The attached patch generates the fast and simple FADD ST(0), ST; instead. It only applies to float,double, real, not to complex numbers.

Created attachment 338 [details] 
Patch against DMD2.029
This will be a useful step towards further optimisation of pure functions with real return values.

Renaming this issue to be less negative

Fixed dmd 1.046 and 2.031