Georg-Johann Lay wrote: > is there a way to prevent gcc 4.3.x from doing bad optimizations? We don't have a -fno-bad-optimizations flag; patches welcome! > I attached an example that shows the performance degradation for > a source compiled with -Os (-O2 is similar) for target avr. > > The code from the new compiler increased by at about 30% > with respect to good old 3.4.6 and needs more as double > of stack slots (13 instead of 6). > > text data bss dec hex filename > 156 0 0 156 9c foo-3.4.6.o > 206 0 0 206 ce foo-4.3.2.o > > Moreover, it expands a rather trivial address computation into a > multiplication on a target without hardware multiplier, so > there is additional, unacceptable time and code penalty > caused by a call to __mulhi3 from libgcc2. > > The multiplication is by -2, i.e. trivial This is strange. Can you provide an example of that address computation as a test case? Make it just a few lines long, please. Andrew.
