ipa-sra: Testcase that removing a "returns_nonnull" retval works

Since we can now remove return values of functions with return_nonnull
type attribute, I'll feel a bit safer if we can test this does not ICE
when someone attempts to access a non-existent call LHS.  Eventually
we should probably drop the attribute when this happens.

gcc/testsuite/ChangeLog:

2021-11-15  Martin Jambor  <mjambor@suse.cz>

	* gcc.dg/ipa/ipa-sra-ret-nonull.c: New test.

1 files changed, 40 insertions, 0 deletions

diff --git a/gcc/testsuite/gcc.dg/ipa/ipa-sra-ret-nonull.c b/gcc/testsuite/gcc.dg/ipa/ipa-sra-ret-nonull.c
new file mode 100644
index 0000000..18c13ef
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/ipa/ipa-sra-ret-nonull.c
@@ -0,0 +1,40 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fdump-ipa-sra-details"  } */
+
+volatile void *gp;
+volatile void *gq;
+char buf[16];
+
+__attribute__((returns_nonnull, noinline))
+static char *
+foo (char *p, char *q)
+{
+  gq = q;
+  gp = p;
+  return q;
+}
+
+__attribute__((returns_nonnull, noinline))
+static char *
+bar (char *p, char *q)
+{
+  return foo (p, q) + 8;
+}
+
+__attribute__((noipa))
+static char *
+get_charp (void)
+{
+  return &buf[0];
+}
+
+int
+main ()
+{
+  char *r;
+  asm volatile ("" : : : "memory");
+  r = bar (get_charp (), get_charp ());
+  return 0;
+}
+
+/* { dg-final { scan-ipa-dump-times "Will SKIP return." 2 "sra" } } */