middle-end/110055 - avoid CLOBBERing static variables

The gimplifier can elide initialized constant automatic variables
to static storage in which case TARGET_EXPR gimplification needs
to avoid emitting a CLOBBER for them since their lifetime is no
longer limited.  Failing to do so causes spurious dangling-pointer
diagnostics on the added testcase for some targets.

Bootstrapped and tested on x86_64-unknown-linux-gnu, pushed.

	PR middle-end/110055
	* gimplify.cc (gimplify_target_expr): Do not emit
	CLOBBERs for variables which have static storage duration
	after gimplifying their initializers.

	* g++.dg/warn/Wdangling-pointer-pr110055.C: New testcase.

gcc/gimplify.cc

@@ -7173,8 +7173,10 @@ gimplify_target_expr (tree *expr_p, gimple_seq *pre_p, gimple_seq *post_p)
 	gimplify_and_add (init, &init_pre_p);
 
       /* Add a clobber for the temporary going out of scope, like
-	 gimplify_bind_expr.  */
+	 gimplify_bind_expr.  But only if we did not promote the
+	 temporary to static storage.  */
       if (gimplify_ctxp->in_cleanup_point_expr
+	  && !TREE_STATIC (temp)
 	  && needs_to_live_in_memory (temp))
 	{
 	  if (flag_stack_reuse == SR_ALL)

gcc/testsuite/g++.dg/warn/Wdangling-pointer-pr110055.C

@@ -0,0 +1,16 @@
+// { dg-do compile }
+// { dg-require-effective-target c++11 }
+// { dg-options "-O3 -fno-exceptions -Wdangling-pointer" }
+
+#include <cstdint>
+#include <vector>
+
+struct Data {
+  std::vector<uint16_t> v = {1, 1};
+};
+
+int main()
+{
+  Data a;
+  Data b;
+}