c++: -Wreturn-type with if (true) throw [PR107310]

I removed this folding in GCC 12 because it was interfering with an
experiment of richi's, but that never went in and the change causes
regressions, so let's put it back.

This reverts commit r12-5638-ga3e75c1491cd2d.

	PR c++/107310

gcc/cp/ChangeLog:

	* cp-gimplify.cc (genericize_if_stmt): Restore folding
	of constant conditions.

gcc/testsuite/ChangeLog:

	* c-c++-common/Wimplicit-fallthrough-39.c: Adjust warning.
	* g++.dg/warn/Wreturn-6.C: New test.

diff --git a/gcc/cp/cp-gimplify.cc b/gcc/cp/cp-gimplify.cc
index 1982f5ba9ce77f90856cd1c728ed4bd93d7d6889..71c55e18557341cfdd72ebf3a98ff7a4eeaf13ca 100644 (file)
--- a/gcc/cp/cp-gimplify.cc
+++ b/gcc/cp/cp-gimplify.cc
@@ -176,6 +176,12 @@ genericize_if_stmt (tree *stmt_p)
     }
   else if (IF_STMT_CONSTEXPR_P (stmt))
     stmt = integer_nonzerop (cond) ? then_ : else_;
+  /* ??? This optimization doesn't seem to belong here, but removing it
+     causes -Wreturn-type regressions (e.g. 107310).  */
+  else if (integer_nonzerop (cond) && !TREE_SIDE_EFFECTS (else_))
+    stmt = then_;
+  else if (integer_zerop (cond) && !TREE_SIDE_EFFECTS (then_))
+    stmt = else_;
   else
     stmt = build3 (COND_EXPR, void_type_node, cond, then_, else_);
   protected_set_expr_location_if_unset (stmt, locus);

diff --git a/gcc/testsuite/c-c++-common/Wimplicit-fallthrough-39.c b/gcc/testsuite/c-c++-common/Wimplicit-fallthrough-39.c
index da4aef3a3182149c5c5e4200fb5a71bf02b035d0..d06bc0db5eccc8531e1565648d58bfc8710d22a0 100644 (file)
--- a/gcc/testsuite/c-c++-common/Wimplicit-fallthrough-39.c
+++ b/gcc/testsuite/c-c++-common/Wimplicit-fallthrough-39.c
@@ -37,8 +37,8 @@ fn2 (int n)
   switch (n)
     {
     case 0:
-      if (1)     /* { dg-warning "statement may fall through" "" { target c++ } } */
-               n++;      /* { dg-warning "statement may fall through" "" { target c } } */
+      if (1)
+               n++;      /* { dg-warning "statement may fall through" } */
     case 1:      /* { dg-message "here" } */
       return -1;
     }

diff --git a/gcc/testsuite/g++.dg/warn/Wreturn-6.C b/gcc/testsuite/g++.dg/warn/Wreturn-6.C
new file mode 100644 (file)
index 0000000..85fef0e
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wreturn-6.C
@@ -0,0 +1,16 @@
+// PR c++/107310
+
+struct f
+{
+  ~f();
+};
+
+int foo(int t) {
+  f g;
+  switch (t) {
+  case 1:
+    return 1;
+  }
+  if (true)
+    throw 1;
+} // { dg-bogus "control reaches end" }