+O[no]entrysched | +Oentrysched allows the optimizer to perform |
| instruction scheduling on a subprogram’s entry and |
| exit code sequences. This option is only effective at |
| optimization level 1 or higher. |
| The option can change the behavior of programs that |
| perform |
| asynchronous interrupts. |
| The default is +Onoentrysched. |
| NOTE: This option is valid only on the |
| systems. |
+O[no]failsafe | Enable [disable] failsafe optimization. When a |
| compilation fails at the current optimization level, |
| +Ofailsafe will automatically restart the |
| compilation at +O2(for specific high level optimizer |
| errors +O3/+O4) or +O1 for Itanium® processor family |
| architecture and +O0 for |
| default is +Ofailsafe. |
+Ofast | Select a combination of compilation options for |
| optimum execution speed of the compiled program. |
| Those options include: +O2, |
| +Olibcalls+Onolimit, +Ofltacc=relaxed, |
| and +FPD. +Ofast also causes the +pi4M, +pd4M |
| options to be passed to the linker. In addition to these |
| options, on the Itanium processor family architecture, |
| +DSnative instruction scheduling is selected and |
| +mergeseg is also passed to the linker. |
+Ofaster | Selects the +Ofast option at optimization level +O3 |
| for |
| family architectures, +Ofaster runs at +O4and implies |
| |
+O[no]fenvaccess | Inform the compiler that the program accesses [does |
| not access] the floating point environment to test flags |
| or run under |
| program does not access the floating point |
| environment, the compiler is allowed to perform certain |
| optimizations that it otherwise may not perform, such |
| as global common subexpression elimination, code |
| motion, or constant folding. |
| The default is +Onofenvaccess. |
+O[no]fastaccess | +Ofastaccess improves execution time by speeding |
| up access to global data items. You can use this option |
| at optimization level 1 or higher. Note that the |
| +Ofastaccess option may increase link time. The |
| default is +Onofastaccess at optimization levels 1, |
| 2, and 3; and +Ofastaccess at optimization level |
| 4. |
| NOTE: This option is valid only on |
+O[no]fltacc | +Onofltacc enables optimizations that follow the |
| rules of algebra but may change the order of |
| expression evaluation. For example, if a, b, and c are |
| |
| c and a + (b + c)may give slightly different results |
| due to roundoff. |
| The +Onofltacc option also enables the fusion of |
| adjacent multiply and add |
| Fused |
| higher, FMA occurs by default.) FMA improves |
| performance but occasionally produces results that |
| may differ in accuracy from results produced by code |
| where fusion has not occurred. In general, the |
| differences are slight. |
42 Compiling and linking