tree-ssa-live: Fix .DEFERRED_INIT handling [PR122184]

remove_unused_locals ignores clobbers in the initial phase (and
some debug stmts) and this has been copied for .DEFERRED_INIT
as well:
          if (gimple_clobber_p (stmt))
            {
              have_local_clobbers = true;
              continue;
            }

          if (gimple_call_internal_p (stmt, IFN_DEFERRED_INIT))
            {
              have_local_clobbers = true;
              continue;
            }
This is so that the second phase can then drop clobbers that
clobber unused local vars and ditto for .DEFERRED_INIT.
Except, for clobbers it does
                /* Remove clobbers referencing unused vars, or clobbers
                   with MEM_REF lhs referencing uninitialized pointers.  */
                if ((VAR_P (base) && !is_used_p (base))
                    || (TREE_CODE (lhs) == MEM_REF
                        && TREE_CODE (TREE_OPERAND (lhs, 0)) == SSA_NAME
                        && SSA_NAME_IS_DEFAULT_DEF (TREE_OPERAND (lhs, 0))
                        && (TREE_CODE (SSA_NAME_VAR (TREE_OPERAND (lhs, 0)))
                            != PARM_DECL)))
so handles both the var = {CLOBBER}; case where var is unused local,
or *SSA_NAME = {CLOBBER} where SSA_NAME is default definition of
non-PARM_DECL, but for .DEFERRED_INIT it doesn't:
                if (DECL_P (base) && !is_used_p (base))
On the following case, we have *SSA_NAME(D) = .DEFERRED_INIT (...);
and because of the former we don't mark the SSA_NAME as used and
because of the latter we keep the .DEFERRED_INIT call, so the SSA_NAME
is freed and later on we ICE because the SSA_NAME in the freelist doesn't
have SSA_NAME_DEF_STMT.

The following patch fixes it by handling .DEFERRED_INIT like clobbers
and dropping them also when it has a MEM_REF with default definition
of SSA_NAME for non-PARM_DECL on the lhs.

2025-11-19  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/122184
	* tree-ssa-live.cc (remove_unused_locals): Drop .DEFERRED_INIT
	calls with MEM_REF lhs based on uninitialized SSA_NAME.

	* g++.dg/opt/pr122184-1.C: New test.
	* g++.dg/opt/pr122184-2.C: New test.

diff --git a/gcc/testsuite/g++.dg/opt/pr122184-1.C b/gcc/testsuite/g++.dg/opt/pr122184-1.C
new file mode 100644 (file)
index 0000000..50f8639
--- /dev/null
+++ b/gcc/testsuite/g++.dg/opt/pr122184-1.C
@@ -0,0 +1,12 @@
+// PR tree-optimization/122184
+// { dg-do compile }
+// { dg-require-stack-check "generic" }
+// { dg-options "-O2 -fstack-check=generic" }
+
+void
+foo ()
+{
+  goto fail;
+  char var[41];
+fail:;
+}

diff --git a/gcc/testsuite/g++.dg/opt/pr122184-2.C b/gcc/testsuite/g++.dg/opt/pr122184-2.C
new file mode 100644 (file)
index 0000000..b5dd6fc
--- /dev/null
+++ b/gcc/testsuite/g++.dg/opt/pr122184-2.C
@@ -0,0 +1,12 @@
+// PR tree-optimization/122184
+// { dg-do compile }
+// { dg-require-stack-check "generic" }
+// { dg-options "-O2 -fstack-check=generic -ftrivial-auto-var-init=zero" }
+
+void
+foo ()
+{
+  goto fail;
+  char var[41];
+fail:;
+}

diff --git a/gcc/tree-ssa-live.cc b/gcc/tree-ssa-live.cc
index 5e0891361dc75ad3b22bda4569b4d7b187f54ed4..46543a1c865b6d2947e85cff93e93aa8abe5b2d4 100644 (file)
--- a/gcc/tree-ssa-live.cc
+++ b/gcc/tree-ssa-live.cc
@@ -926,7 +926,12 @@ remove_unused_locals (void)
              {
                tree lhs = gimple_call_lhs (stmt);
                tree base = get_base_address (lhs);
-               if (DECL_P (base) && !is_used_p (base))
+               if ((DECL_P (base) && !is_used_p (base))
+                   || (TREE_CODE (lhs) == MEM_REF
+                       && TREE_CODE (TREE_OPERAND (lhs, 0)) == SSA_NAME
+                       && SSA_NAME_IS_DEFAULT_DEF (TREE_OPERAND (lhs, 0))
+                       && (TREE_CODE (SSA_NAME_VAR (TREE_OPERAND (lhs, 0)))
+                           != PARM_DECL)))
                  {
                    unlink_stmt_vdef (stmt);
                    gsi_remove (&gsi, true);