On Thu, 4 Aug 2022, Tamar Christina wrote:
> Hi All,
>
> The failures on -m32 on x86 show that the checks at the top level in
> tree_ssa_phiopt_worker aren't enough for diamond_p.
>
> In minmax_replacement we perform the additional validation of the shape but by
> then it's too late to catch these case.
>
> This patch changes it so we check that for a diamond shape we check that the
> edges we're operation on must result in the same destination BB.
>
> We also enforce that for a diamond the middle BBs must have a single
> successor,
> this is because the remainder of the code always follows EDGE_SUCC 0. If
> there
> are more than 1 successor then the edge we follow could be not part of the
> diamond so just reject it early on.
>
> I also remove the assert after the use of gimple_phi_arg_def as this function
> can't return NULL. if the index is out of range it already breaks on an assert
> inside the gimple_phi_arg_def, so we never hit this assert.
>
> Bootstrapped Regtested on aarch64-none-linux-gnu, x86_64-pc-linux-gnu
> and no issues.
>
> Ok for master?
>
> Thanks,
> Tamar
>
> gcc/ChangeLog:
>
> PR middle-end/106519
> * tree-ssa-phiopt.cc (tree_ssa_phiopt_worker): Check final phi edge for
> diamond shapes.
>
> gcc/testsuite/ChangeLog:
>
> PR middle-end/106519
> * gcc.dg/pr106519.c: New test.
>
> --- inline copy of patch --
> diff --git a/gcc/testsuite/gcc.dg/pr106519.c b/gcc/testsuite/gcc.dg/pr106519.c
> new file mode 100644
> index
> 0000000000000000000000000000000000000000..3d4662d8a02c6501560abb71ac53320f093620d8
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/pr106519.c
> @@ -0,0 +1,11 @@
> +/* { dg-do compile } */
> +
> +int bytestart, bytemem_0_0, modlookup_l_p;
> +
> +void
> +modlookup_l() {
> + long j;
> + while (modlookup_l_p)
> + while (bytestart && j && bytemem_0_0)
> + j = j + 1;
> +}
> diff --git a/gcc/tree-ssa-phiopt.cc b/gcc/tree-ssa-phiopt.cc
> index
> a8e55e040649e17f83a2fc3340e368cf9c4c5e70..1c4942b5b5c18732a8b18789c04e2685437404dd
> 100644
> --- a/gcc/tree-ssa-phiopt.cc
> +++ b/gcc/tree-ssa-phiopt.cc
> @@ -268,7 +268,8 @@ tree_ssa_phiopt_worker (bool do_store_elim, bool
> do_hoist_loads, bool early_p)
> continue;
> }
> else if (EDGE_SUCC (bb1, 0)->dest == EDGE_SUCC (bb2, 0)->dest
> - && !empty_block_p (bb1))
> + && !empty_block_p (bb1)
> + && single_succ_p (bb1) && single_succ_p (bb2))
> diamond_p = true;
> else
> continue;
> @@ -311,6 +312,12 @@ tree_ssa_phiopt_worker (bool do_store_elim, bool
> do_hoist_loads, bool early_p)
> for (gsi = gsi_start (phis); !gsi_end_p (gsi); gsi_next (&gsi))
> {
> phi = as_a <gphi *> (gsi_stmt (gsi));
> +
> + /* A diamond must continue to the same destination node,
> otherwise
> + by definition it's not a diamond. */
> + if (diamond_p && e1->dest != e2->dest)
this and the check below looks redundant since we already check
EDGE_SUCC (bb1, 0)->dest == EDGE_SUCC (bb2, 0)->dest when setting
diamond_p = true? Which means we already verify that following
edge 0 we have a diamond?
In fact for the testcase we _do_ have a diamond but we failed to
adjust e2 to point to the merge block early, we only do it here:
e2 = diamond_p ? EDGE_SUCC (bb2, 0) : e2;
phi = single_non_singleton_phi_for_edges (phis, e1, e2);
That also means that the do_store_elim case possibly wants a
bail out on diamond_p? Not sure for value_replacement.
At least
diff --git a/gcc/tree-ssa-phiopt.cc b/gcc/tree-ssa-phiopt.cc
index a8e55e04064..ef4c0b78f4e 100644
--- a/gcc/tree-ssa-phiopt.cc
+++ b/gcc/tree-ssa-phiopt.cc
@@ -269,7 +269,10 @@ tree_ssa_phiopt_worker (bool do_store_elim, bool
do_hoist_loads, bool early_p)
}
else if (EDGE_SUCC (bb1, 0)->dest == EDGE_SUCC (bb2, 0)->dest
&& !empty_block_p (bb1))
- diamond_p = true;
+ {
+ diamond_p = true;
+ e2 = EDGE_SUCC (bb2, 0);
+ }
else
continue;
@@ -324,7 +327,6 @@ tree_ssa_phiopt_worker (bool do_store_elim, bool
do_hoist_loads, bool early_p)
if (!candorest)
continue;
- e2 = diamond_p ? EDGE_SUCC (bb2, 0) : e2;
phi = single_non_singleton_phi_for_edges (phis, e1, e2);
if (!phi)
continue;
fixes the ICE for me but I did no further checking.
> + continue;
> +
> arg0 = gimple_phi_arg_def (phi, e1->dest_idx);
> arg1 = gimple_phi_arg_def (phi, e2->dest_idx);
> if (value_replacement (bb, bb1, e1, e2, phi, arg0, arg1) == 2)
> @@ -329,12 +336,15 @@ tree_ssa_phiopt_worker (bool do_store_elim, bool
> do_hoist_loads, bool early_p)
> if (!phi)
> continue;
>
> - arg0 = gimple_phi_arg_def (phi, e1->dest_idx);
> - arg1 = gimple_phi_arg_def (phi, e2->dest_idx);
> + /* A diamond must continue to the same destination node, otherwise
> + by definition it's not a diamond. */
> + if (diamond_p && e1->dest != e2->dest)
> + continue;
>
> /* Something is wrong if we cannot find the arguments in the PHI
> node. */
> - gcc_assert (arg0 != NULL_TREE && arg1 != NULL_TREE);
> + arg0 = gimple_phi_arg_def (phi, e1->dest_idx);
> + arg1 = gimple_phi_arg_def (phi, e2->dest_idx);
>
> gphi *newphi;
> if (single_pred_p (bb1)
>
>
>
>
>
--
Richard Biener <rguent...@suse.de>
SUSE Software Solutions Germany GmbH, Frankenstrasse 146, 90461 Nuernberg,
Germany; GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman;
HRB 36809 (AG Nuernberg)
