[PATCH] fix PR c++/77804 - ICE on placement VLA new

[Martin Sebor]

The attached patch removes an assumption from the implementation
of the -Wplacement-new warning that the size of the array type
enclosed in parentheses and accepted by G++ as an extension is
constant.  The assumption causes an ICE in 6.2.0 and 7.0.

Is the patch good to commit to both 7.0 and the 6 branch?

Thanks
Martin

PR c++/77804 - Internal compiler error on incorrect initialization of new-d array

gcc/cp/ChangeLog:
2016-10-03  Martin Sebor  <mse...@redhat.com>

	PR c++/77804
	* init.c (warn_placement_new_too_small): Avoid assuming an array type
	has a constant size.

gcc/testsuite/ChangeLog:
2016-10-03  Martin Sebor  <mse...@redhat.com>

	PR c++/77804
	* g++.dg/warn/Wplacement-new-size-4.C: New test.

diff --git a/gcc/cp/init.c b/gcc/cp/init.c
index 798de08..30957f1 100644
--- a/gcc/cp/init.c
+++ b/gcc/cp/init.c
@@ -2504,7 +2504,7 @@ warn_placement_new_too_small (tree type, tree nelts, tree size, tree oper)
 	      && warn_placement_new < 2)
 	    return;
 	}
-	  
+
       /* The size of the buffer can only be adjusted down but not up.  */
       gcc_checking_assert (0 <= adjust);
 
@@ -2526,8 +2526,13 @@ warn_placement_new_too_small (tree type, tree nelts, tree size, tree oper)
       else if (nelts && CONSTANT_CLASS_P (nelts))
 	  bytes_need = tree_to_uhwi (nelts)
 	    * tree_to_uhwi (TYPE_SIZE_UNIT (type));
-      else
+      else if (tree_fits_uhwi_p (TYPE_SIZE_UNIT (type)))
 	bytes_need = tree_to_uhwi (TYPE_SIZE_UNIT (type));
+      else
+	{
+	  /* The type is a VLA.  */
+	  return;
+	}
 
       if (bytes_avail < bytes_need)
 	{
diff --git a/gcc/testsuite/g++.dg/warn/Wplacement-new-size-4.C b/gcc/testsuite/g++.dg/warn/Wplacement-new-size-4.C
new file mode 100644
index 0000000..da9b1ab
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wplacement-new-size-4.C
@@ -0,0 +1,14 @@
+// PR c++/77804 - Internal compiler error on incorrect initialization of
+// new-d array
+// { dg-do compile }
+// { dg-additional-options "-Wplacement-new -Wvla -Wno-error=vla" }
+
+void* operator new[] (__SIZE_TYPE__ n, void *p) { return p; }
+
+int main()
+{
+    char buf[256];
+    unsigned n = 10;
+    int* p = new (buf) (int[n]);  // { dg-warning "non-constant array new length must be specified without parentheses around the type-id" }
+    //  { dg-warning "ISO C\\+\\+ forbids variable length array" "vla warning" { target *-*-* } .-1 }
+}