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)
