Observed when building Code::Blocks -- uses (wx)Scintilla 3.2.2:
Compiling with -mrcp (this makes the compiler use a 2-step Newton-Raphson approximation with SSE2 reciprocal instructions for divide and square root) disables the "cursor up" function (i.e. nothing happens when you hit the up-arrow key) on semi-random lines in a document. Which lines are inaccessible changes when you scroll the window.
---> Floating-point == comparison used in line calculation causing problem?
GCC does emit a couple of warnings about floatingpoint comparisons, too (platform.h lines 123, 124, editor.cxx lines 428, 506, 567, 2210, 2481, 2826, 2944, 3193, 3285, 3381, 3944, 5102, 6486)
Older versions (e.g. 2.2.9) which do not have XYPOSITION/XYACCUMULATOR as floating point work fine.