[gcc/devel/sphinx] gimple, internal-fn: Add IFN_TRAP and use it for __builtin_unreachable [PR106099]

[Martin Liska <marxin@gcc.gnu.org>]

https://gcc.gnu.org/g:3a4cd5dc6faca8fed7fa256c4c06f4999b5a1f9c

commit 3a4cd5dc6faca8fed7fa256c4c06f4999b5a1f9c
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Thu Jul 28 12:42:14 2022 +0200

    gimple, internal-fn: Add IFN_TRAP and use it for __builtin_unreachable [PR106099]
    
    __builtin_unreachable and __ubsan_handle_builtin_unreachable don't
    use vops, they are marked const/leaf/noreturn/nothrow/cold.
    But __builtin_trap uses vops, isn't const, just leaf/noreturn/nothrow/cold.
    This is I believe so that when users explicitly use __builtin_trap in their
    sources they get stores visible at the trap side.
    -fsanitize=unreachable -fsanitize-undefined-trap-on-error used to transform
    __builtin_unreachable to __builtin_trap even in the past, but the sanopt pass
    has TODO_update_ssa, so it worked fine.
    
    Now that gimple_build_builtin_unreachable can build a __builtin_trap call
    right away, we can run into problems that whenever we need it we would need
    to either manually or through TODO_update* ensure the vops being updated.
    
    Though, as it is originally __builtin_unreachable which is just implemented
    as trap, I think for this case it is fine to avoid vops.  For this the
    patch introduces IFN_TRAP, which has ECF_* flags like __builtin_unreachable
    and is expanded as __builtin_trap.
    
    2022-07-28  Jakub Jelinek  <jakub@redhat.com>
    
            PR tree-optimization/106099
            * internal-fn.def (TRAP): New internal fn.
            * internal-fn.h (expand_TRAP): Declare.
            * internal-fn.cc (expand_TRAP): Define.
            * gimple.cc (gimple_build_builtin_unreachable): For BUILT_IN_TRAP,
            use internal fn rather than builtin.
    
            * gcc.dg/ubsan/pr106099.c: New test.

Diff:
---
 gcc/gimple.cc                         | 11 ++++++++++-
 gcc/internal-fn.cc                    |  6 ++++++
 gcc/internal-fn.def                   |  4 ++++
 gcc/internal-fn.h                     |  1 +
 gcc/testsuite/gcc.dg/ubsan/pr106099.c | 10 ++++++++++
 5 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/gcc/gimple.cc b/gcc/gimple.cc
index 9b156399ba1..cd5ad0c718b 100644
--- a/gcc/gimple.cc
+++ b/gcc/gimple.cc
@@ -430,7 +430,16 @@ gimple_build_builtin_unreachable (location_t loc)
 {
   tree data = NULL_TREE;
   tree fn = sanitize_unreachable_fn (&data, loc);
-  gcall *g = gimple_build_call (fn, data != NULL_TREE, data);
+  gcall *g;
+  if (DECL_FUNCTION_CODE (fn) != BUILT_IN_TRAP)
+    g = gimple_build_call (fn, data != NULL_TREE, data);
+  else
+    {
+      /* Instead of __builtin_trap use .TRAP, so that it doesn't
+	 need vops.  */
+      gcc_checking_assert (data == NULL_TREE);
+      g = gimple_build_call_internal (IFN_TRAP, 0);
+    }
   gimple_set_location (g, loc);
   return g;
 }
diff --git a/gcc/internal-fn.cc b/gcc/internal-fn.cc
index 28973d957fb..aa7c482e968 100644
--- a/gcc/internal-fn.cc
+++ b/gcc/internal-fn.cc
@@ -4494,3 +4494,9 @@ expand_SPACESHIP (internal_fn, gcall *stmt)
   if (!rtx_equal_p (target, ops[0].value))
     emit_move_insn (target, ops[0].value);
 }
+
+void
+expand_TRAP (internal_fn, gcall *)
+{
+  expand_builtin_trap ();
+}
diff --git a/gcc/internal-fn.def b/gcc/internal-fn.def
index 7c398baadc8..7bf661ca376 100644
--- a/gcc/internal-fn.def
+++ b/gcc/internal-fn.def
@@ -456,6 +456,10 @@ DEF_INTERNAL_FN (SHUFFLEVECTOR, ECF_CONST | ECF_LEAF | ECF_NOTHROW, NULL)
 /* <=> optimization.  */
 DEF_INTERNAL_FN (SPACESHIP, ECF_CONST | ECF_LEAF | ECF_NOTHROW, NULL)
 
+/* __builtin_trap created from/for __builtin_unreachable.  */
+DEF_INTERNAL_FN (TRAP, ECF_CONST | ECF_LEAF | ECF_NORETURN
+		       | ECF_NOTHROW | ECF_COLD, NULL)
+
 #undef DEF_INTERNAL_INT_FN
 #undef DEF_INTERNAL_FLT_FN
 #undef DEF_INTERNAL_FLT_FLOATN_FN
diff --git a/gcc/internal-fn.h b/gcc/internal-fn.h
index 23c014a963c..c4c94f80d51 100644
--- a/gcc/internal-fn.h
+++ b/gcc/internal-fn.h
@@ -242,6 +242,7 @@ extern void expand_internal_call (internal_fn, gcall *);
 extern void expand_PHI (internal_fn, gcall *);
 extern void expand_SHUFFLEVECTOR (internal_fn, gcall *);
 extern void expand_SPACESHIP (internal_fn, gcall *);
+extern void expand_TRAP (internal_fn, gcall *);
 
 extern bool vectorized_internal_fn_supported_p (internal_fn, tree);
 
diff --git a/gcc/testsuite/gcc.dg/ubsan/pr106099.c b/gcc/testsuite/gcc.dg/ubsan/pr106099.c
new file mode 100644
index 00000000000..e3f17b34681
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/ubsan/pr106099.c
@@ -0,0 +1,10 @@
+/* PR tree-optimization/106099 */
+/* { dg-do compile } */
+/* { dg-options "-O -fsanitize=unreachable -fsanitize-undefined-trap-on-error -fno-tree-ccp -fno-tree-dominator-opts" } */
+
+void
+foo (void)
+{
+  for (unsigned i = 0; i == 0; i++)
+    ;
+}