The byte tracking of call LHS didn't properly handle possibly
throwing calls correctly which cases bogus DSE and in turn, for the
testcase a bogus uninit diagnostic and (unreliable) wrong-code.
Bootstrapped and tested on x86_64-unknown-linux-gnu, pushed.
PR tree-optimization/109434
* tree-ssa-dse.cc (initialize_ao_ref_for_dse): Properly
handle possibly throwing calls when processing the LHS
and may-defs are not OK.
* g++.dg/opt/pr109434.C: New testcase.
---
gcc/testsuite/g++.dg/opt/pr109434.C | 28 ++++++++++++++++++++++++++++
gcc/tree-ssa-dse.cc | 3 ++-
2 files changed, 30 insertions(+), 1 deletion(-)
create mode 100644 gcc/testsuite/g++.dg/opt/pr109434.C
diff --git a/gcc/testsuite/g++.dg/opt/pr109434.C
b/gcc/testsuite/g++.dg/opt/pr109434.C
new file mode 100644
index 00000000000..cffa327fd9b
--- /dev/null
+++ b/gcc/testsuite/g++.dg/opt/pr109434.C
@@ -0,0 +1,28 @@
+// { dg-do compile }
+// { dg-require-effective-target c++17 }
+// { dg-options "-O2 -Wall" }
+
+#include <optional>
+#include <stdexcept>
+
+std::optional<int> foo()
+{
+ volatile int x = 1;
+ if (x)
+ throw std::runtime_error("haha");
+ return 42;
+}
+
+int main()
+{
+ std::optional<int> optInt;
+ try {
+ // We falsely DSEd the LHS of the call even though foo throws
+ // which results in an uninitialized diagnostic
+ optInt = foo();
+ } catch (...) {
+ return optInt.has_value();
+ }
+ std::optional<double> optDbl{optInt};
+ return optDbl ? optDbl.value () : 2.0;
+}
diff --git a/gcc/tree-ssa-dse.cc b/gcc/tree-ssa-dse.cc
index 4f8a44fbba0..eabe8ba4522 100644
--- a/gcc/tree-ssa-dse.cc
+++ b/gcc/tree-ssa-dse.cc
@@ -179,7 +179,8 @@ initialize_ao_ref_for_dse (gimple *stmt, ao_ref *write,
bool may_def_ok = false)
}
if (tree lhs = gimple_get_lhs (stmt))
{
- if (TREE_CODE (lhs) != SSA_NAME)
+ if (TREE_CODE (lhs) != SSA_NAME
+ && (may_def_ok || !stmt_could_throw_p (cfun, stmt)))
{
ao_ref_init (write, lhs);
return true;
--
2.35.3
