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.

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;
 }

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 ();
+}

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

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);
 

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++)
+    ;
+}