> > > > When this function replaces the edge it doesn't seem to update the
> > > dominators.
> > > > Since It's replacing the middle BB we then end up with an error
> > > >
> > > > gcc/testsuite/gcc.dg/tree-ssa/minmax-14.c:17:1: error: dominator
> > > > of 5 should be 4, not 2
> > > >
> > > > during early verify. So instead, I replace the BB but defer its
> > > > deletion until cleanup which removes it and updates the dominators.
> > >
> > > Hmm, for a diamond shouldn't you replace
> > >
> > > if (EDGE_SUCC (cond_block, 0)->dest == bb)
> > > edge_to_remove = EDGE_SUCC (cond_block, 1);
> > > else
> > > edge_to_remove = EDGE_SUCC (cond_block, 0);
> > >
> > > with
> > >
> > > if (EDGE_SUCC (cond_block, 0)->dest == bb)
> > > edge_to_remove = EDGE_SUCC (cond_block, 1);
> > > else if (EDGE_SUCC (cond_block, 1)->dest == bb)
> > > edge_to_remove = EDGE_SUCC (cond_block, 0);
> > >
> > > thus, the code expects to be left with a fallthru to the PHI block
> > > which is expected to have the immediate dominator being cond_block
> > > but with a diamond there's a (possibly empty) block inbetween and
> > > dominators are wrong.
> >
> > Agreed, but the (EDGE_SUCC (cond_block, 1)->dest == bb) doesn't seem
> > like the Right one since for a diamond there will be a block in
> > between the two. Did you perhaps mean EDGE_SUCC (EDGE_SUCC
> > (cond_block, 1)->dest, 0)->dest == bb? i.e. that that destination across the
> diamond be bb, and then you remove the middle block?
>
> Hmm, I think my condition was correct - the code tries to remove the edge to
> the middle-block and checks the remaining edge falls through to the merge
> block. With a true diamond there is no fallthru to the merge block to keep so
> we better don't remove any edge?
>
> > For the minmax diamond we want both edges removed, since all the code
> > in the middle BBs are now dead. But this is probably not true in the
> > general
> sense.
Ah! Sorry I was firing a few cylinders short, I get what you mean now:
@@ -425,8 +439,19 @@ replace_phi_edge_with_variable (basic_block cond_block,
edge edge_to_remove;
if (EDGE_SUCC (cond_block, 0)->dest == bb)
edge_to_remove = EDGE_SUCC (cond_block, 1);
- else
+ else if (EDGE_SUCC (cond_block, 1)->dest == bb)
edge_to_remove = EDGE_SUCC (cond_block, 0);
+ else
+ {
+ /* If neither edge from the conditional is the final bb
+ then we must have a diamond block, in which case
+ the true edge was changed by SET_USE above and we must
+ mark the other edge as the false edge. */
+ gcond *cond = as_a <gcond *> (last_stmt (cond_block));
+ gimple_cond_make_false (cond);
+ return;
+ }
+
Bootstrapped Regtested on aarch64-none-linux-gnu and no issues.
Ok with this Change?
Thanks,
Tamar
