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| -rw-r--r-- | tcg/README | 10 |
1 files changed, 9 insertions, 1 deletions
diff --git a/tcg/README b/tcg/README index 660012281f..cfdfd96d09 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 |