[PATCH]Save/restore crtl->is_thunk for emitting thunk code (PR/debug 39378)

[Jing Yu <jingyuuiuc at gmail dot com>]

?This patch is to fix the bug PR/debug 39378 that crtl is not reset
?after emitting thunk functions. The thunk is emitted with crtl->is_thunk=1,
and the thunk target function is also emitted
?with crtl->is_thunk=1. The bug exposes if compiled with -mthumb flag
?on arm-eabi backend, where the generated binary causes segmentation
?fault, because the thunk target function is coded in 32 bit mode, but
?the thunk calls the target via arm-to-thunk approach.

The fix is that save crtl->is_thunk before the call to lang_hooks.callgraph.emit
_associated_thunks() in cgraph_expand_function(), and restore crtl->is_thunk
after the call.
I also add a test case to make sure the bug will not happen again.

DejaGNU test:
I built the toolchain with GNU trunk GCC (gcc version
4.4.0 20090305) and newlib, and tested it on the arm emulator.
This patch does not trigger more regression errors or warnings.

Target: arm-eabi
Configured with: /home/jingyu/projects/gcc/gcc_src/configure
--prefix=/home/jingyu/local/gcc_arm_eabi --target=arm-eabi
--build=i686-linux --host=i686-linux --enable-multilib --with-newlib
--with-gnu-as --with-gnu-ld --enable-languages=c,c++
Thread model: single
gcc version 4.4.0 20090305 (experimental) (GCC)

Thanks,
Jing


Index: gcc/cgraphunit.c
===================================================================
--- gcc/cgraphunit.c??? (revision 144771)
+++ gcc/cgraphunit.c??? (working copy)
@@ -1043,7 +1043,11 @@

?? /* Generate RTL for the body of DECL.? */
?? if (lang_hooks.callgraph.emit_associated_thunks)
-??? lang_hooks.callgraph.emit_associated_thunks (decl);
+??? {
+????? bool is_thunk = crtl->is_thunk;
+????? lang_hooks.callgraph.emit_associated_thunks (decl);
+????? crtl->is_thunk = is_thunk;
+??? }
?? tree_rest_of_compilation (decl);

?? /* Make sure that BE didn't give up on compiling.? */

Index: gcc/testsuite/g++.dg/inherit/thunk10.C
===================================================================
--- gcc/testsuite/g++.dg/inherit/thunk10.C????? (revision 0)
+++ gcc/testsuite/g++.dg/inherit/thunk10.C????? (revision 0)
@@ -0,0 +1,61 @@
+/* { dg-options "-mthumb" { target arm*-*-* } } */
+/* { dg-do run } */
+/* { dg-timeout 10 } */
+
+/* PR target/39378 */
+/* Check if the thunk target function is emitted correctly. */
+class B1
+{
+public:
+? virtual int foo1(void);
+? int b1;
+};
+
+
+class B2
+{
+public:
+? virtual int foo2 (void);
+? int b2;
+};
+
+class D : public B1, public B2
+{
+? int foo1(void);
+? int foo2(void);
+? int d;
+};
+
+int B1::foo1(void)
+{
+? return 3;
+}
+
+int B2::foo2(void)
+{
+? return 4;
+}
+
+int D::foo1(void)
+{
+? return 1;
+}
+
+int D::foo2(void)
+{
+? return 2;
+}
+
+__attribute__((noinline)) int test(B2* bp)
+{
+? return bp->foo2();
+}
+
+int main()
+{
+? B2 *bp = new D();
+? if (test(bp) == 2)
+??? return 0;
+? else
+??? return 1;
+}