On Fri, Dec 30, 2011 at 5:58 PM, Dmitry Melnik <d...@ispras.ru> wrote: > After Thumb-2's peephole2 adds flag clobbering on suitable insns in order to > generate 16-bit encoding for them, if-conversion can't transform these insns > into cond_execs. In theory, if the instruction were converted to > conditional form, it would also use 16-bit encoding, so the flag clobbering > doesn't have to be added to force 16-bit encoding. > Swapping order of these passes has actually increased the number of > if-conversions (it results in 2% more it-blocks on SPEC2K INT and > 4% more "long" it-blocks that contain two or more instructions). However, > this actually caused 2038 code size regression on SPEC2K INT. At first, we > blamed this growth on the effects described in patches 1-4, but with these > fixes the regression has only reduced by 474 bytes. I.e. the more there are > conditional insns, the better is the code size reduction from patches 1-4, > but altered pass order still loses 1564 bytes to the original one. > What do you think about the order of these passes on Thumb-2? > > (The patch is obvious, and is not attached).
I suppose switching them makes sense because if-conversion can create new peephole opportunities. Not sure if the reverse is also true? Richard.
