Hi!
The gimplifier uses in several places STRIP_USELESS_TYPE_CONVERSION and
that, being primarily a middle-end predicate, doesn't like error_mark_nodes
appearing in conversion operands. I've talked about it with Richi on IRC
and he'd prefer not to change it.
The reason we end up with them is because cp_fold when it sees a NOP_EXPR
conversion to void, it does nothing, and when cp_fold_r is used, it folds
the operand to in this case error_mark_node and nothing adjusts the
conversion.
As cp_fold has a cache, the following shouldn't really be expensive and will
just handle the case of error_mark_node right and the rest as before.
A variant (which I have a patch for too) would be to cp_fold_rvalue the
operand and if it folded to something different and is not error_mark_node
build a new NOP_EXPR around it. What I don't like about that too much is
that for a very common case (aren't most statements converted to void) we
would probably create many more trees, as cp_fold generally doesn't modify stuff
in place, while cp_fold_r does. By doing what the following patch does we
won't create the extra NOP_EXPRs in all cases where the operand folds
somehow.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2018-01-02 Jakub Jelinek <ja...@redhat.com>
PR c++/83634
* cp-gimplify.c (cp_fold) <case NOP_EXPR>: If the operand folds to
error_mark_node, return error_mark_node.
* g++.dg/parse/pr83634.C: New test.
--- gcc/cp/cp-gimplify.c.jj 2017-12-14 21:11:40.616124411 +0100
+++ gcc/cp/cp-gimplify.c 2018-01-02 13:23:51.946128057 +0100
@@ -2112,7 +2112,20 @@ cp_fold (tree x)
case NON_LVALUE_EXPR:
if (VOID_TYPE_P (TREE_TYPE (x)))
- return x;
+ {
+ /* This is just to make sure we don't end up with casts to
+ void from error_mark_node. If we just return x, then
+ cp_fold_r might fold the operand into error_mark_node and
+ leave the conversion in the IR. STRIP_USELESS_TYPE_CONVERSION
+ during gimplification doesn't like such casts.
+ Don't create a new tree if op0 != TREE_OPERAND (x, 0), the
+ folding of the operand should be in the caches and if in cp_fold_r
+ it will modify it in place. */
+ op0 = cp_fold (TREE_OPERAND (x, 0));
+ if (op0 == error_mark_node)
+ x = error_mark_node;
+ break;
+ }
loc = EXPR_LOCATION (x);
op0 = cp_fold_maybe_rvalue (TREE_OPERAND (x, 0), rval_ops);
--- gcc/testsuite/g++.dg/parse/pr83634.C.jj 2018-01-02 12:39:44.500517833
+0100
+++ gcc/testsuite/g++.dg/parse/pr83634.C 2018-01-02 12:35:17.399462088
+0100
@@ -0,0 +1,11 @@
+// PR c++/83634
+// { dg-do compile }
+
+void
+foo ()
+{
+ const int x = fn (); // { dg-error "was not declared in this scope" }
+ short n;
+ for (n = x; n < 100; ++n)
+ ;
+}
Jakub
