This bug was an object/value confusion; we are interested in the size
of *b.ip, but instead the code was calculating the size of b.ip itself.
This seems to be because compute_objsize will compute the size of whatever
object it can find in the argument: if you pass it a VAR_DECL, it gives you
the size of that variable. If you pass it an ADDR_EXPR of a VAR_DECL, it
again gives you the size of the variable. The way you can tell the
difference is by looking at the deref member of access_ref: if it's -1, the
argument is a pointer to the object. Since that's what we're interested in,
we should check for that, like check_dangling_stores does.
This regressed some tests because compute_objsize_r was wrongly zeroing
deref in the POINTER_PLUS_EXPR handling; adding an offset to a pointer
doesn't change whether the pointer is itself a variable or a pointer to
one. In fact, handling POINTER_PLUS_EXPR only really makes sense for deref
== -1, where we're adjusting a pointer to the variable.
Tested x86_64-pc-linux-gnu, OK for trunk?
PR c++/100370
gcc/cp/ChangeLog:
* init.cc (warn_placement_new_too_small): Check deref.
gcc/ChangeLog:
* pointer-query.cc (compute_objsize_r) [POINTER_PLUS_EXPR]: Require
deref == -1.
gcc/testsuite/ChangeLog:
* g++.dg/warn/Wplacement-new-size-11.C: New test.
---
gcc/cp/init.cc | 5 +++++
gcc/pointer-query.cc | 7 ++++---
.../g++.dg/warn/Wplacement-new-size-11.C | 15 +++++++++++++++
3 files changed, 24 insertions(+), 3 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/warn/Wplacement-new-size-11.C
diff --git a/gcc/cp/init.cc b/gcc/cp/init.cc
index 01e762320f3..43097121244 100644
--- a/gcc/cp/init.cc
+++ b/gcc/cp/init.cc
@@ -2811,6 +2811,11 @@ warn_placement_new_too_small (tree type, tree nelts,
tree size, tree oper)
if (!objsize)
return;
+ /* We can only draw conclusions if ref.deref == -1,
+ i.e. oper is the address of the object. */
+ if (ref.deref != -1)
+ return;
+
offset_int bytes_avail = wi::to_offset (objsize);
offset_int bytes_need;
diff --git a/gcc/pointer-query.cc b/gcc/pointer-query.cc
index 4390535ef56..d93657f3206 100644
--- a/gcc/pointer-query.cc
+++ b/gcc/pointer-query.cc
@@ -2299,9 +2299,10 @@ compute_objsize_r (tree ptr, gimple *stmt, bool addr,
int ostype,
if (!compute_objsize_r (ref, stmt, addr, ostype, pref, snlim, qry))
return false;
- /* Clear DEREF since the offset is being applied to the target
- of the dereference. */
- pref->deref = 0;
+ /* The below only makes sense if the offset is being applied to the
+ address of the object. */
+ if (pref->deref != -1)
+ return false;
offset_int orng[2];
tree off = pref->eval (TREE_OPERAND (ptr, 1));
diff --git a/gcc/testsuite/g++.dg/warn/Wplacement-new-size-11.C
b/gcc/testsuite/g++.dg/warn/Wplacement-new-size-11.C
new file mode 100644
index 00000000000..a6fe82e90ae
--- /dev/null
+++ b/gcc/testsuite/g++.dg/warn/Wplacement-new-size-11.C
@@ -0,0 +1,15 @@
+// PR c++/100370
+// { dg-do compile { target c++11 } }
+
+using size_t = decltype(sizeof(1));
+inline void *operator new (size_t s, void *p) { return p; }
+
+int main()
+{
+ struct s1 { int iv[4]; };
+ struct s2 { union { char* cp; int* ip; }; };
+
+ s2 b;
+ b.ip=new int[8];
+ new (b.ip+4) s1; // { dg-bogus "-Wplacement-new" }
+}
base-commit: 44fe49401725055a740ce47e80561b6932b8cd01
--
2.27.0
