[PATCH] c++: Fix bogus warnings about ignored annotations [PR114409]

[Jakub Jelinek]

Hi!

The middle-end warns about the ANNOTATE_EXPR added for while/for loops
if they declare a var inside of the loop condition.
This is because the assumption is that ANNOTATE_EXPR argument is used
immediately in a COND_EXPR (later GIMPLE_COND), but simplify_loop_decl_cond
wraps the ANNOTATE_EXPR inside of a TRUTH_NOT_EXPR, so it no longer
holds.

The following patch fixes that by adding the TRUTH_NOT_EXPR inside of the
ANNOTATE_EXPR argument if any.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

Note, the PR is mostly about ICE with the annotations used in a template,
this patch doesn't change anything on that and I really don't know what
should be done in that case.

2024-03-22  Jakub Jelinek  <ja...@redhat.com>

        PR c++/114409
        * semantics.cc (simplify_loop_decl_cond): Use cp_build_unary_op with
        TRUTH_NOT_EXPR on ANNOTATE_EXPR argument (if any) rather than
        ANNOTATE_EXPR itself.

        * g++.dg/ext/pr114409.C: New test.

--- gcc/cp/semantics.cc.jj      2024-03-01 17:27:58.862888609 +0100
+++ gcc/cp/semantics.cc 2024-03-21 15:24:57.296857864 +0100
@@ -799,7 +799,11 @@ simplify_loop_decl_cond (tree *cond_p, t
   *cond_p = boolean_true_node;
 
   if_stmt = begin_if_stmt ();
-  cond = cp_build_unary_op (TRUTH_NOT_EXPR, cond, false, tf_warning_or_error);
+  cond_p = &cond;
+  while (TREE_CODE (*cond_p) == ANNOTATE_EXPR)
+    cond_p = &TREE_OPERAND (*cond_p, 0);
+  *cond_p = cp_build_unary_op (TRUTH_NOT_EXPR, *cond_p, false,
+                              tf_warning_or_error);
   finish_if_stmt_cond (cond, if_stmt);
   finish_break_stmt ();
   finish_then_clause (if_stmt);
--- gcc/testsuite/g++.dg/ext/pr114409.C.jj      2024-03-21 15:27:44.077661090 
+0100
+++ gcc/testsuite/g++.dg/ext/pr114409.C 2024-03-21 15:27:15.331039726 +0100
@@ -0,0 +1,22 @@
+// PR c++/114409
+// { dg-do compile }
+// { dg-options "-O2 -Wall" }
+
+void qux (int);
+int foo (int);
+
+void
+bar (int x)
+{
+  #pragma GCC novector
+  while (int y = foo (x))      // { dg-bogus "ignoring loop annotation" }
+    qux (y);
+}
+
+void
+baz (int x)
+{
+  #pragma GCC novector
+  for (; int y = foo (x); )    // { dg-bogus "ignoring loop annotation" }
+    qux (y);
+}

        Jakub