rs6000: Handle pcrel sibcalls to longcall functions [PR104894]

Before PCREL in POWER10, we were not allowed to perform sibcalls to longcall
functions since callee's return would skip the TOC restore in the caller.
However, with PCREL we can now safely perform a sibling call to longcall
functions.  The problem with the current code is that pcrel sibcall
branches to a PLT stub label even though -fno-plt was used.  The solution
here is to check for a pcrel longcall and emit an inline plt stub in
that case.

2022-04-11  Peter Bergner  <bergner@linux.ibm.com>

gcc/
	PR target/104894
	* config/rs6000/rs6000.cc (rs6000_sibcall_aix): Handle pcrel sibcalls
	to longcall functions.

gcc/testsuite/
	PR target/104894
	* gcc.target/powerpc/pr104894.c: New test.
	* gcc.target/powerpc/pr104894-2.c: New test.

3 files changed, 53 insertions, 2 deletions

diff --git a/gcc/config/rs6000/rs6000.cc b/gcc/config/rs6000/rs6000.cc
index ceaddaf..bc61959 100644
--- a/gcc/config/rs6000/rs6000.cc
+++ b/gcc/config/rs6000/rs6000.cc
@@ -25678,11 +25678,20 @@ rs6000_sibcall_aix (rtx value, rtx func_desc, rtx tlsarg, rtx cookie)
   rtx r12 = NULL_RTX;
   rtx func_addr = func_desc;
 
-  gcc_assert (INTVAL (cookie) == 0);
-
   if (global_tlsarg)
     tlsarg = global_tlsarg;
 
+  /* Handle longcall attributes.  */
+  if (INTVAL (cookie) & CALL_LONG && SYMBOL_REF_P (func_desc))
+    {
+      /* PCREL can do a sibling call to a longcall function
+	 because we don't need to restore the TOC register.  */
+      gcc_assert (rs6000_pcrel_p ());
+      func_desc = rs6000_longcall_ref (func_desc, tlsarg);
+    }
+  else
+    gcc_assert (INTVAL (cookie) == 0);
+
   /* For ELFv2, r12 and CTR need to hold the function address
      for an indirect call.  */
   if (GET_CODE (func_desc) != SYMBOL_REF && DEFAULT_ABI == ABI_ELFv2)
diff --git a/gcc/testsuite/gcc.target/powerpc/pr104894-2.c b/gcc/testsuite/gcc.target/powerpc/pr104894-2.c
new file mode 100644
index 0000000..d1a011e
--- /dev/null
+++ b/gcc/testsuite/gcc.target/powerpc/pr104894-2.c
@@ -0,0 +1,22 @@
+/* PR target/104894 */
+/* { dg-require-effective-target powerpc_elfv2 } */
+/* { dg-require-effective-target power10_ok } */
+/* { dg-options "-O2 -mdejagnu-cpu=power10 -fno-plt" } */
+
+/* Verify we do not ICE on the following test case and that we emit one
+   indirect call and one indirect sibcall, with r12 and CTR containing
+   the function addresses.  */
+
+void foo (void);
+
+void
+bar (void)
+{
+  foo ();
+  foo ();
+}
+
+/* { dg-final { scan-assembler-times {\mmtctr 12\M} 2 } } */
+/* { dg-final { scan-assembler-times {\mbctrl\M} 1 } } */
+/* { dg-final { scan-assembler-times {\mbctr\M} 1 } } */
+/* { dg-final { scan-assembler-not {\mbl\M} } } */
diff --git a/gcc/testsuite/gcc.target/powerpc/pr104894.c b/gcc/testsuite/gcc.target/powerpc/pr104894.c
new file mode 100644
index 0000000..f46fe88
--- /dev/null
+++ b/gcc/testsuite/gcc.target/powerpc/pr104894.c
@@ -0,0 +1,20 @@
+/* PR target/104894 */
+/* { dg-require-effective-target powerpc_elfv2 } */
+/* { dg-require-effective-target power10_ok } */
+/* { dg-options "-O2 -mdejagnu-cpu=power10 -fno-plt" } */
+
+/* Verify we do not ICE on the following test case and that we emit an
+   indirect sibcall, with r12 and CTR containing the function address.  */
+
+void foo (void);
+
+void
+bar (void)
+{
+  foo ();
+}
+
+/* { dg-final { scan-assembler-times {\mmtctr 12\M} 1 } } */
+/* { dg-final { scan-assembler-times {\mbctr\M} 1 } } */
+/* { dg-final { scan-assembler-not {\mbl\M} } } */
+/* { dg-final { scan-assembler-not {\mbctrl\M} } } */