10th June 2008
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Administrator
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Join Date: Apr 2008
Location: pl_PL.lodz
Posts: 1,056
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from gcc.gnu.org manual:
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-O also turns on -fomit-frame-pointer on machines where doing so does not interfere with debugging.
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Quote:
-fomit-frame-pointer
Don't keep the frame pointer in a register for functions that don't need one. This avoids the instructions to save, set up and restore frame pointers; it also makes an extra register available in many functions. It also makes debugging impossible on some machines.
On some machines, such as the VAX, this flag has no effect, because the standard calling sequence automatically handles the frame pointer and nothing is saved by pretending it doesn't exist. The machine-description macro FRAME_POINTER_REQUIRED controls whether a target machine supports this flag. See Register Usage.
Enabled at levels -O, -O2, -O3, -Os.
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rest: http://gcc.gnu.org/onlinedocs/gcc-4....timize-Options
Also -fomit-frame-pointer does good things on C code, but it may break C++ code, so use only for C.
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