Hi Michael and John, Thank you for your replies. I managed to get around it for my particular case: determining the performance difference of the "-fif-conversion" option. I copy this to the list in case someone else has similar problem in the future. You're both right on that the "-fif-conversion" option works only with certain optimization level specified, such as "-O" and "-O2". And you can turn it off by "-fno-if-conversion". So "-O2 -fno-if-conversion" would compile the code with all the optimization options in O2 default except for "-fif-conversion". For general case, link: http://gcc.gnu.org/onlinedocs/gcc-4.3.3/gcc/Optimize-Options.html#Optimize-Options says: "Options of the form -fflag specify machine-independent flags. Most flags have both positive and negative forms; the negative form of -ffoo would be -fno-foo." Please correct if I misunderstand anything. Thank you. LC On Mon, Jul 20, 2009 at 6:15 PM, Michael Meissner<meissner@xxxxxxxxxxxxxxxxxx> wrote: > On Mon, Jul 20, 2009 at 05:37:29PM -0400, Lingchuan (LC) Meng wrote: >> Hi all, >> >> I'm trying to enable gcc 4.3.2 on Ubuntu to compile C code with >> support of conditional moves. (and Conditional Moves as the only >> enabled optimization) >> >> I can see CMOVxx in the assembly compiled with "-O" option. However, >> no CMOVxx is found in the assembly generated with just >> "-fif-conversion" option. >> >> More surprisingly (well, at least to me), I listed all the enabled >> optimization options of "-O", and put them in one line. Then I >> compiled the same code as: > > Several optimizations require a certain optimization level, and are not done > even if you specify the -f option. If conversion is one such optimization, > where the functions gate_handle_if_conversion and > gate_handle_if_conversion_after_combine, and > gate_handle_if_conversion_after_reload in ifcvt.c all have explicit tests for > optimize being greater than 0 in addition to the -f option flag(s). I would > suspect this is because if conversion needs some of the dataflow passes that > are not normally run for -O0. From the ChangeLogs, it looks like the functions > were originally added in July 2005. > > -- > Michael Meissner, IBM > 4 Technology Place Drive, MS 2203A, Westford, MA, 01886, USA > meissner@xxxxxxxxxxxxxxxxxx > -- Best regards, Lingchuan Meng
