Re: C++ PATCH to tweak cp_fully_fold (PR c++/84590)

[Marek Polacek <polacek@redhat.com>]

On Thu, Mar 01, 2018 at 02:29:47PM -0500, Jason Merrill wrote:
> I think this should happen in the block with maybe_constant_value;
> cp_fold_rvalue doesn't do this.

This, then:

Bootstrapped/regtested on x86_64-linux, ok for trunk?

2018-03-01  Marek Polacek  <polacek@redhat.com>

	PR c++/84590
	* cp-gimplify.c (cp_fully_fold): Unwrap TARGET_EXPR or a CONSTRUCTOR
	wrapped in VIEW_CONVERT_EXPR.

	* c-c++-common/ubsan/shift-11.c: New test.

diff --git gcc/cp/cp-gimplify.c gcc/cp/cp-gimplify.c
index 55a9d278dbe..0ddd435454c 100644
--- gcc/cp/cp-gimplify.c
+++ gcc/cp/cp-gimplify.c
@@ -2037,7 +2037,17 @@ cp_fully_fold (tree x)
   /* FIXME cp_fold ought to be a superset of maybe_constant_value so we don't
      have to call both.  */
   if (cxx_dialect >= cxx11)
-    x = maybe_constant_value (x);
+    {
+      x = maybe_constant_value (x);
+      /* Sometimes we are given a CONSTRUCTOR but the call above wraps it into
+	 a TARGET_EXPR; undo that here.  */
+      if (TREE_CODE (x) == TARGET_EXPR)
+	x = TARGET_EXPR_INITIAL (x);
+      else if (TREE_CODE (x) == VIEW_CONVERT_EXPR
+	       && TREE_CODE (TREE_OPERAND (x, 0)) == CONSTRUCTOR
+	       && TREE_TYPE (TREE_OPERAND (x, 0)) == TREE_TYPE (x))
+	x = TREE_OPERAND (x, 0);
+    }
   return cp_fold_rvalue (x);
 }
 
diff --git gcc/testsuite/c-c++-common/ubsan/shift-11.c gcc/testsuite/c-c++-common/ubsan/shift-11.c
index e69de29bb2d..03a72e217a2 100644
--- gcc/testsuite/c-c++-common/ubsan/shift-11.c
+++ gcc/testsuite/c-c++-common/ubsan/shift-11.c
@@ -0,0 +1,13 @@
+/* PR c++/84590 */
+/* { dg-do compile } */
+/* { dg-options "-fsanitize=shift" } */
+
+struct S {
+  int b;
+};
+
+void
+fn (void)
+{
+  struct S c1 = { 1 << -1 }; /* { dg-warning "left shift" } */
+}

	Marek