On 05/14/2013 08:16 AM, Richard Henderson wrote: > On 05/14/2013 07:05 AM, Claudio Fontana wrote: >>> Conditional branch range is +-1MB. You'll never see a TB that large. You >>> don't need to emit a branch-across-branch. >> >> Is there maybe a way to do it right even in the corner case where we have >> a huge list of hundreds of thousands of instructions without jumps and then >> a conditional jump? >> Are we _guaranteed_ to never see that large a TB with some kind of define, >> similarly to MAX_CODE_GEN_BUFFER_SIZE? > > There are three mechanisms that all limit TB size: > (1) OPC_MAX_SIZE, limiting the number of opcodes emitted, > (2) CF_COUNT_MASK, limiting the number of instructions translated, > (3) Instruction pointer crossing a page boundary, where we end a TB > and re-verify the page protection bits of the new page. > > Nr 1 is probably the most significant, since it most directly relates to > the number of output instructions, and thus the resulting TB size.
BTW, for comparison, tcg/s390/tcg-target.c works well enough with just 16 bits on the relative branch insns; eight times smaller than your 19 bits. r~
