Hi!
C++17 and later say
"The postfix-expression is sequenced before each expression in the
expression-list
and any default argument."
As the following testcase shows, we don't honor that. Either
cp_gimplify_expr gimplifies some arguments (if CALL_EXPR_REVERSE_ARGS
or CALL_EXPR_ORDERED_ARGS or for !CALL_EXPR_OPERATOR_SYNTAX) and then
the postfix-expression's side-effects are evaluated after those arguments
that are pregimplified by cp_gimplify_expr, or, even if cp_gimplify_expr
doesn't do anything, gimplify_call_expr will:
/* There is a sequence point before the call, so any side effects in
the calling expression must occur before the actual call. Force
gimplify_expr to use an internal post queue. */
ret = gimplify_expr (&CALL_EXPR_FN (*expr_p), pre_p, NULL,
is_gimple_call_addr, fb_rvalue);
before gimplifying args, which is fine if there are side-effects, but
doesn't help the actual testcase, because say a user VAR_DECL or PARM_DECL
or RESULT_DECL with pointer to function type satisfies is_gimple_call_addr
predicate, so it will actually be evaluated only later after the arguments
are evaluated, which can actually overwrite the VAR_DECL etc.
So, the following patch gimplifies the postfix expression (CALL_EXPR_FN)
early, and if it isn't invariant or TYPE_OBJ_REF or SSA_NAME (in that case
we don't have to worry about something overwriting it), forces it into a
temporary.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2019-10-03 Jakub Jelinek <ja...@redhat.com>
PR c++/91974
* cp-gimplify.c (cp_gimplify_expr) <case CALL_EXPR>: For
-fstrong-eval-order ensure CALL_EXPR_FN side-effects are evaluated
before any arguments. Additionally, ensure CALL_EXPR_FN that isn't
invariant nor OBJ_TYPE_REF nor SSA_NAME is forced into a temporary.
* g++.dg/cpp1z/eval-order5.C: New test.
--- gcc/cp/cp-gimplify.c.jj 2019-10-03 00:26:22.184804539 +0200
+++ gcc/cp/cp-gimplify.c 2019-10-03 10:01:50.769221516 +0200
@@ -818,6 +818,21 @@ cp_gimplify_expr (tree *expr_p, gimple_s
case CALL_EXPR:
ret = GS_OK;
+ if (flag_strong_eval_order == 2
+ && CALL_EXPR_FN (*expr_p)
+ && cp_get_callee_fndecl_nofold (*expr_p) == NULL_TREE)
+ {
+ enum gimplify_status t
+ = gimplify_expr (&CALL_EXPR_FN (*expr_p), pre_p, NULL,
+ is_gimple_call_addr, fb_rvalue);
+ if (t == GS_ERROR)
+ ret = GS_ERROR;
+ else if (is_gimple_variable (CALL_EXPR_FN (*expr_p))
+ && TREE_CODE (CALL_EXPR_FN (*expr_p)) != SSA_NAME)
+ CALL_EXPR_FN (*expr_p)
+ = get_initialized_tmp_var (CALL_EXPR_FN (*expr_p), pre_p,
+ NULL);
+ }
if (!CALL_EXPR_FN (*expr_p))
/* Internal function call. */;
else if (CALL_EXPR_REVERSE_ARGS (*expr_p))
--- gcc/testsuite/g++.dg/cpp1z/eval-order5.C.jj 2019-10-03 10:37:13.442990472
+0200
+++ gcc/testsuite/g++.dg/cpp1z/eval-order5.C 2019-10-03 10:38:31.082812256
+0200
@@ -0,0 +1,31 @@
+// PR c++/91974
+// { dg-do run }
+// { dg-options "-fstrong-eval-order" }
+
+extern "C" void abort ();
+
+bool ok = false;
+
+void
+foo (int x)
+{
+ if (x != 0)
+ abort ();
+ ok = true;
+}
+
+void
+bar (int)
+{
+ abort ();
+}
+
+int
+main ()
+{
+ typedef void (*T) (int);
+ T fn = foo;
+ fn ((fn = bar, 0));
+ if (fn != bar || !ok)
+ abort ();
+}
Jakub
