Ping? On 22 June 2011 15:40, Peter Maydell <peter.mayd...@linaro.org> wrote: > Expand the note on the number of TCG ops generated per target insn, > to be clearer about the range of applicability of the 20 op rule > of thumb. Also add a note about the hard MAX_OP_PER_INSTR limit. > > Signed-off-by: Peter Maydell <peter.mayd...@linaro.org> > --- > The expansion of the first bullet point is based on remarks by > Aurelien in this email: > http://lists.gnu.org/archive/html/qemu-devel/2011-06/msg00395.html > > tcg/README | 10 +++++++++- > 1 files changed, 9 insertions(+), 1 deletions(-) > > diff --git a/tcg/README b/tcg/README > index 6600122..cfdfd96 100644 > --- a/tcg/README > +++ b/tcg/README > @@ -504,7 +504,15 @@ register. > - Don't hesitate to use helpers for complicated or seldom used target > instructions. There is little performance advantage in using TCG to > implement target instructions taking more than about twenty TCG > - instructions. > + instructions. Note that this rule of thumb is more applicable to > + helpers doing complex logic or arithmetic, where the C compiler has > + scope to do a good job of optimisation; it is less relevant where > + the instruction is mostly doing loads and stores, and in those cases > + inline TCG may still be faster for longer sequences. > + > +- The hard limit on the number of TCG instructions you can generate > + per target instruction is set by MAX_OP_PER_INSTR in exec-all.h -- > + you cannot exceed this without risking a buffer overrun. > > - Use the 'discard' instruction if you know that TCG won't be able to > prove that a given global is "dead" at a given program point. The > -- > 1.7.1 > > >
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