Given
template <typename T>
void foo () { T A::*fptr; }
We don't know whether fptr is a pointer-to-member-function or a
pointer-to-data-member until we know what T is. But until then, fptr
gets the type OFFSET_TYPE.
If we later instantiate foo with e.g. T = void() then we know that fptr
is a pointer-to-member-function and so we give the specialized copy of
fptr a type which satisfies TYPE_PTRMEMFUNC_P (some RECORD_TYPE). The
placeholder OFFSET_TYPE and the resulting RECORD_TYPE however have
different sizes and modes (DI vs TI on x86_64), but the DECL_MODE of the
specialized copy of fptr never gets updated accordingly. This stale
DECL_MODE eventually leads the backend to miscompile copies to and from
fptr.
[ Some more analysis at
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70096#c4 ]
This patch makes tsubst_decl clear the DECL_MODE of the new decl so that
the subsequent call to layout_type can update it accordingly.
Tested on x86_64-pc-linux-gnu. Does this patch look OK to commit?
gcc/cp/ChangeLog:
PR c++/70096
* pt.c (tsubst_decl): Clear the DECL_MODE of the new decl.
gcc/testsuite/ChangeLog:
PR c++/70096
* g++.dg/template/ptrmem30.C: New test.
---
gcc/cp/pt.c | 2 ++
gcc/testsuite/g++.dg/template/ptrmem30.C | 45 ++++++++++++++++++++++++++++++++
2 files changed, 47 insertions(+)
create mode 100644 gcc/testsuite/g++.dg/template/ptrmem30.C
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index f9c5b0b..ebfc45b 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -12374,6 +12374,8 @@ tsubst_decl (tree t, tree args, tsubst_flags_t complain)
/* The initializer must not be expanded until it is required;
see [temp.inst]. */
DECL_INITIAL (r) = NULL_TREE;
+ if (VAR_P (r))
+ DECL_MODE (r) = VOIDmode;
if (CODE_CONTAINS_STRUCT (TREE_CODE (t), TS_DECL_WRTL))
SET_DECL_RTL (r, NULL);
DECL_SIZE (r) = DECL_SIZE_UNIT (r) = 0;
diff --git a/gcc/testsuite/g++.dg/template/ptrmem30.C
b/gcc/testsuite/g++.dg/template/ptrmem30.C
new file mode 100644
index 0000000..923238b
--- /dev/null
+++ b/gcc/testsuite/g++.dg/template/ptrmem30.C
@@ -0,0 +1,45 @@
+// PR c++/70096
+// { dg-do run }
+
+int read;
+
+struct Holder
+{
+ void foo () { read = data; }
+ int data;
+};
+
+void
+poison_stack ()
+{
+ volatile char a[256];
+ __builtin_memset ((void *)a, 0xa, sizeof a);
+}
+
+template <typename F>
+void test1 ()
+{
+ Holder h;
+ h.data = 42;
+ F Holder::*fptr = &Holder::foo;
+ (h.*fptr)();
+}
+
+template <typename F>
+void test2 ()
+{
+ Holder h;
+ h.data = 42;
+ F Holder::*fptr1 = &Holder::foo;
+ F Holder::*fptr2 = fptr1;
+ (h.*fptr2)();
+}
+
+
+int main ()
+{
+ poison_stack ();
+ test1<void()>();
+ poison_stack ();
+ test2<void()>();
+}
--
2.8.0.rc3.27.gade0865
