[gcc r11-3397] c: Fix -Wduplicated-branches ICE [PR97125]

[Marek Polacek]

https://gcc.gnu.org/g:c48ffe21f8f3478cf08f9442e3f973df358caf2a

commit r11-3397-gc48ffe21f8f3478cf08f9442e3f973df358caf2a
Author: Marek Polacek <polacek@redhat.com>
Date:   Sun Sep 20 16:11:00 2020 -0400

    c: Fix -Wduplicated-branches ICE [PR97125]
    
    We crash here because since r11-3302 the C FE uses codes like SWITCH_STMT
    in the else branches in the attached test, and inchash::add_expr in
    do_warn_duplicated_branches doesn't handle these front-end codes.  In
    the C++ FE this works because by the time we get to do_warn_duplicated_branches
    we've already cp_genericize'd the SWITCH_STMT tree into a SWITCH_EXPR.
    
    The fix is to call do_warn_duplicated_branches_r only after loops and other
    structured control constructs have been lowered.
    
    gcc/c-family/ChangeLog:
    
            PR c/97125
            * c-gimplify.c (c_genericize): Only call do_warn_duplicated_branches_r
            after loops and other structured control constructs have been lowered.
    
    gcc/testsuite/ChangeLog:
    
            PR c/97125
            * c-c++-common/Wduplicated-branches-15.c: New test.

Diff:
---
 gcc/c-family/c-gimplify.c                          |  8 +++---
 .../c-c++-common/Wduplicated-branches-15.c         | 32 ++++++++++++++++++++++
 2 files changed, 36 insertions(+), 4 deletions(-)

diff --git a/gcc/c-family/c-gimplify.c b/gcc/c-family/c-gimplify.c
index 8b326c99d48..d1e391590dd 100644
--- a/gcc/c-family/c-gimplify.c
+++ b/gcc/c-family/c-gimplify.c
@@ -533,10 +533,6 @@ c_genericize (tree fndecl)
 		 &pset);
     }
 
-  if (warn_duplicated_branches)
-    walk_tree_without_duplicates (&DECL_SAVED_TREE (fndecl),
-				  do_warn_duplicated_branches_r, NULL);
-
   /* Genericize loops and other structured control constructs.  The C++
      front end has already done this in lang-specific code.  */
   if (!c_dialect_cxx ())
@@ -550,6 +546,10 @@ c_genericize (tree fndecl)
       pop_cfun ();
     }
 
+  if (warn_duplicated_branches)
+    walk_tree_without_duplicates (&DECL_SAVED_TREE (fndecl),
+				  do_warn_duplicated_branches_r, NULL);
+
   /* Dump the C-specific tree IR.  */
   dump_orig = get_dump_info (TDI_original, &local_dump_flags);
   if (dump_orig)
diff --git a/gcc/testsuite/c-c++-common/Wduplicated-branches-15.c b/gcc/testsuite/c-c++-common/Wduplicated-branches-15.c
new file mode 100644
index 00000000000..d4943607086
--- /dev/null
+++ b/gcc/testsuite/c-c++-common/Wduplicated-branches-15.c
@@ -0,0 +1,32 @@
+/* PR c/97125 */
+/* { dg-do compile } */
+/* { dg-options "-Wduplicated-branches" } */
+
+void foo (void);
+
+void
+fn1 (void)
+{
+  if (0)
+    foo ();
+  else
+    switch (0);
+}
+
+void
+fn2 (void)
+{
+  if (0)
+    foo ();
+  else
+    while (0);
+}
+
+void
+fn3 (void)
+{
+  if (0)
+    foo ();
+  else
+    for (;;);
+}