Objective-C: fix crash with -fobjc-nilcheck

When -fobjc-nilcheck is enabled, messages that result in a struct type should
yield a zero-initialized struct when sent to nil.  Currently, the frontend
crashes when it encounters this situation.  This patch fixes the crash by
generating the tree for the `{}` initializer.

Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>
Co-authored-by: Matt Jacobson  <mhjacobson@me.com>

	PR objc/101666

gcc/objc/ChangeLog:

	* objc-act.c (objc_build_constructor): Handle empty constructor
	lists.
	* objc-next-runtime-abi-02.c (build_v2_objc_method_fixup_call):
	Handle nil receivers.
	(build_v2_build_objc_method_call): Likewise.

gcc/testsuite/ChangeLog:

	* obj-c++.dg/pr101666-0.mm: New test.
	* obj-c++.dg/pr101666-1.mm: New test.
	* obj-c++.dg/pr101666.inc: New.
	* objc.dg/pr101666-0.m: New test.
	* objc.dg/pr101666-1.m: New test.
	* objc.dg/pr101666.inc: New.

3 files changed, 46 insertions, 0 deletions

diff --git a/gcc/testsuite/objc.dg/pr101666-0.m b/gcc/testsuite/objc.dg/pr101666-0.m
new file mode 100644
index 0000000..5f87f60
--- /dev/null
+++ b/gcc/testsuite/objc.dg/pr101666-0.m
@@ -0,0 +1,7 @@
+/* { dg-do run } */
+/* { dg-skip-if "NeXT only" { *-*-* } { "-fgnu-runtime" } { "" } } */
+/* { dg-skip-if "ABI 2 only" { *-*-* && { ! objc2 } } { "*" } { "" } } */
+/* { dg-additional-options "-fobjc-nilcheck -Wno-objc-root-class" } */
+
+#include "pr101666.inc"
+
diff --git a/gcc/testsuite/objc.dg/pr101666-1.m b/gcc/testsuite/objc.dg/pr101666-1.m
new file mode 100644
index 0000000..41ef370
--- /dev/null
+++ b/gcc/testsuite/objc.dg/pr101666-1.m
@@ -0,0 +1,10 @@
+/* Later versions of Darwin can compile for 10.5, but cannot link it so we
+   can only run this test up to 10.13.  */
+/* { dg-do compile { target *-*-darwin* } } */
+/* { dg-do run { target *-*-darwin[89]* *-*-darwin1[0-7]* } } */
+/* { dg-skip-if "NeXT only" { *-*-* } { "-fgnu-runtime" } { "" } } */
+/* { dg-skip-if "ABI 2 only" { *-*-* && { ! objc2 } } { "*" } { "" } } */
+/* { dg-additional-options "-fobjc-nilcheck -mmacosx-version-min=10.5 " } */
+/* { dg-additional-options "-Wno-objc-root-class" } */
+
+#include "pr101666.inc"
diff --git a/gcc/testsuite/objc.dg/pr101666.inc b/gcc/testsuite/objc.dg/pr101666.inc
new file mode 100644
index 0000000..f1dddca
--- /dev/null
+++ b/gcc/testsuite/objc.dg/pr101666.inc
@@ -0,0 +1,29 @@
+#include <stdlib.h>
+struct point { double x, y, z; };
+
+@interface Foo
+- (struct point)bar;
+- (struct point)baz;
+@end
+
+@implementation Foo
+- (struct point)bar { struct point q = { 1.0, 2.0, 3.0 }; return q; };
+- (struct point)baz { struct point q = { 4.0, 5.0, 6.0 }; return q; };
+@end
+
+/* Cases where a check for nil should be inserted by the compiler, when
+   -fobjc-nilcheck is in force. We should not attempt the calls, and the
+   result should be 0-filled. */
+
+Foo *f;
+
+int main(void) {
+  struct point p = [f bar];
+  if (p.x != 0.0 || p.y != 0.0 || p.z != 0.0)
+    abort ();
+  id nilobj = (id)0;
+  p = [nilobj baz];
+  if (p.x != 0.0 || p.y != 0.0 || p.z != 0.0)
+    abort ();
+  return 0;
+}