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https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=6e3e708dbadaae7b504af7fc4410015624793f02
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109434
From 6e3e708dbadaae7b504af7fc4410015624793f02 Mon Sep 17 00:00:00 2001
From: Richard Biener <rguenther@suse.de>
Date: Tue, 11 Apr 2023 15:06:59 +0200
Subject: [PATCH] tree-optimization/109434 - bogus DSE of throwing call LHS
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.
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.
--- /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;
+}
--- 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;
--
2.31.1
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