This is the mail archive of the egcs@egcs.cygnus.com mailing list for the EGCS project. See the EGCS home page for more information.
At 22:28 +0000 3/6/99, craig@jcb-sc.com wrote: >>I would prefer to do this. I think we should be doing just a tad >>more work in "no optimization" mode, primarily in terms of getting >>rid of unreachable code. >> > . .... > My feeling is, if the optimization is likely to save as much (or more) > overall compile/link time as, say, twice as much as it costs, it's > probably worth turning on for -O0. > > E.g. folding constants, done for -O0, costs time up front, but saves > all sorts of code-generation time down the line -- in later RTL > phases, in generated the .s file, in running the assembler, the > linker, and the loader, etc. > Measurement that the CMU BLISS-11 developers made bear this out. They found that running with full optimization that the total execution time was lower than with optimization off. (That was for a DEC-10 hosted cross compiler (36 bit words generating code for a 16 bit machine. For Bliss32, the results were less conclusive, but that compiler generated object code directly without emitting assembly source as an intermediate. The only fly in this ointment is that OCCASIONALLY even the simple optimizations have bugs in 'em; so having a way to force absolutely minimal optimization is still desirable. -- Al Lehotsky ------------------------------------------------------------------------ Quality Software Management http://www.tiac.net/users/lehotsky lehotsky@tiac.net (978)287-0435 Voice (978)287-0436 Fax/Data Software Process Improvement and Management Consulting Language Design and Compiler Implementation