>> @@ -671,11 +668,9 @@ convert_control_dep_chain_into_preds (vec<edge>
>> *dep_chains,
>> e = one_cd_chain[j];
>> guard_bb = e->src;
>> gsi = gsi_last_bb (guard_bb);
>> + /* Ignore empty BBs as they're basically forwarder blocks. */
>> if (gsi_end_p (gsi))
>> - {
>> - has_valid_pred = false;
>> - break;
>> - }
>> + continue;
>> cond_stmt = gsi_stmt (gsi);
>> if (is_gimple_call (cond_stmt) && EDGE_COUNT (e->src->succs) >= 2)
>> /* Ignore EH edge. Can add assertion on the other edge's flag. */
> ISTM that you want to use empty_block_p (bb) && single_succ_p (bb) to
> detect the forwarder block. Otherwise ISTM that labels and debug
> statements would affect the uninit analysis.
We still need to check for gsi_end_p() because guard_bb can have no
statements but be considered non empty according to empty_block_p().
This is the case with a seemingly empty basic block that actually has
an incoming PHI.
Jakub suggested the following patch which fixes the new ICE in the PR.
I've adjusted the comments accordingly.
OK?
gcc/
PR middle-end/81897
* tree-ssa-uninit.c (convert_control_dep_chain_into_preds): Skip
empty blocks.
diff --git a/gcc/testsuite/gcc.dg/uninit-pr81897-2.c b/gcc/testsuite/gcc.dg/uninit-pr81897-2.c
new file mode 100644
index 00000000000..3960af454e5
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/uninit-pr81897-2.c
@@ -0,0 +1,35 @@
+/* { dg-do compile } */
+/* { dg-options "-O1 -fno-tree-ccp -Wmaybe-uninitialized" } */
+
+int oo;
+
+void
+pc (int *tt)
+{
+ int cf = 0;
+
+ if (*tt != 0)
+ {
+ if (0)
+ {
+ int *qg;
+ int uj = 0;
+
+ t6:
+ tt = &cf;
+ if (oo != 0)
+ {
+ ++uj; /* { dg-warning "may be used uninit" } */
+ *qg = !!oo && !!uj; /* { dg-warning "may be used uninit" } */
+ }
+ }
+ cf = 0;
+ goto t6;
+ }
+
+ if (oo != 0)
+ {
+ *tt = 1;
+ goto t6;
+ }
+}
diff --git a/gcc/tree-ssa-uninit.c b/gcc/tree-ssa-uninit.c
index 38239476286..8ccbc85970a 100644
--- a/gcc/tree-ssa-uninit.c
+++ b/gcc/tree-ssa-uninit.c
@@ -669,9 +669,16 @@ convert_control_dep_chain_into_preds (vec<edge> *dep_chains,
e = one_cd_chain[j];
guard_bb = e->src;
gsi = gsi_last_bb (guard_bb);
- /* Ignore empty BBs as they're basically forwarder blocks. */
+ /* Ignore empty forwarder blocks. */
if (empty_block_p (guard_bb) && single_succ_p (guard_bb))
continue;
+ /* An empty basic block here is likely a PHI, and is not one
+ of the cases we handle below. */
+ if (gsi_end_p (gsi))
+ {
+ has_valid_pred = false;
+ break;
+ }
cond_stmt = gsi_stmt (gsi);
if (is_gimple_call (cond_stmt) && EDGE_COUNT (e->src->succs) >= 2)
/* Ignore EH edge. Can add assertion on the other edge's flag. */
