On 09/13/11 15:05, Richard Sandiford wrote: > It just feels like checking for trap_if or turning off cross-jumping > are working around problems in the representation of shrink-wrapped > functions. There should be something in the IL to say that those > two blocks cannot be merged for CFI reasons.
There is - JUMP_LABELs and such, and the simple_return vs return distinction. This works for essentially all the interesting cases. The problem here is that we don't have a jump as the last insn. So how about the solution in crossjumping as below? > Maybe two flags on > the basic block to say whether they start (resp. end) with the > "wrapped" version of the CFI? (Which unfortunately would need > to be checked explicitly.) I think that's overdesigning it, and it breaks as soon as something discards the bb info (reorg...) or puts a label in the middle of a prologue or epilogue. Keeping that up-to-date would be much more fragile than just manually dealing with the few cases where we can't tell what's going on. > OTOH, if another reviewer thinks that's unreasnable, I'll happily > defer to them. Cc'ing rth for a second opinion... Bernd
* cfgcleanup.c (outgoing_edges_match): Nonjump edges to the EXIT_BLOCK_PTR match only if we did not perform shrink-wrapping. Index: gcc/cfgcleanup.c =================================================================== --- gcc/cfgcleanup.c (revision 178734) +++ gcc/cfgcleanup.c (working copy) @@ -1488,6 +1488,16 @@ outgoing_edges_match (int mode, basic_bl edge e1, e2; edge_iterator ei; + /* If we performed shrink-wrapping, edges to the EXIT_BLOCK_PTR can + only be distinguished for JUMP_INSNs. The two paths may differ in + whether they went through the prologue. Sibcalls are fine, we know + that we either didn't need or inserted an epilogue before them. */ + if (flag_shrink_wrap + && single_succ_p (bb1) && single_succ (bb1) == EXIT_BLOCK_PTR + && !JUMP_P (BB_END (bb1)) + && !(CALL_P (BB_END (bb1)) && SIBLING_CALL_P (BB_END (bb1)))) + return false; + /* If BB1 has only one successor, we may be looking at either an unconditional jump, or a fake edge to exit. */ if (single_succ_p (bb1)