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f01bfe5c6d
This has the side effect of confusing gcc-4.2.1's optimizer into more often doing the right thing. When it does the wrong thing here, it seems to be mainly making too many copies of x with dependency chains. This effect is tiny on amd64, but in some cases on i386 it is enormous. E.g., on i386 (A64) with -O1, the current version of exp2() should take about 50 cycles, but took 83 cycles before this change and 66 cycles after this change. exp2f() with -O1 only speeded up from 51 to 47 cycles. (exp2f() should take about 40 cycles, on an Athlon in either i386 or amd64 mode, and now takes 42 on amd64). exp2l() with -O1 slowed down from 155 cycles to 123 for some args; this is unimportant since the i386 exp2l() is a fake; the wrong thing for it seems to involve branch misprediction. |
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| ld80 | ||
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| man | ||
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| src | ||
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