The x86_64 psABI says that an empty class isn't passed or returned in memory
or registers, so we shouldn't set %eax in this function. This seems like a
missed case from the GCC 8 TYPE_EMPTY_P changes.
Shall I apply this for GCC 9, or hold it for stage 1?
* function.c (expand_function_end): Don't copy a TYPE_EMPTY_P
result.
---
gcc/function.c | 8 +++++---
gcc/testsuite/g++.dg/opt/empty3.C | 8 ++++++++
gcc/ChangeLog | 6 ++++++
3 files changed, 19 insertions(+), 3 deletions(-)
create mode 100644 gcc/testsuite/g++.dg/opt/empty3.C
diff --git a/gcc/function.c b/gcc/function.c
index dc035707c20..f5998bbeb5e 100644
--- a/gcc/function.c
+++ b/gcc/function.c
@@ -5338,9 +5338,11 @@ expand_function_end (void)
tree decl_result = DECL_RESULT (current_function_decl);
rtx decl_rtl = DECL_RTL (decl_result);
- if (REG_P (decl_rtl)
- ? REGNO (decl_rtl) >= FIRST_PSEUDO_REGISTER
- : DECL_REGISTER (decl_result))
+ if ((REG_P (decl_rtl)
+ ? REGNO (decl_rtl) >= FIRST_PSEUDO_REGISTER
+ : DECL_REGISTER (decl_result))
+ /* Unless the ABI says not to. */
+ && !TYPE_EMPTY_P (TREE_TYPE (decl_result)))
{
rtx real_decl_rtl = crtl->return_rtx;
complex_mode cmode;
diff --git a/gcc/testsuite/g++.dg/opt/empty3.C
b/gcc/testsuite/g++.dg/opt/empty3.C
new file mode 100644
index 00000000000..93ca9abc22c
--- /dev/null
+++ b/gcc/testsuite/g++.dg/opt/empty3.C
@@ -0,0 +1,8 @@
+// PR c++/88529
+// { dg-do compile { target c++11 } }
+// { dg-final { scan-assembler-not mov { target x86_64-*-* } } }
+// The x86_64 psABI says that f() doesn't put the return value anywhere.
+
+class A{};
+
+A f() { return {}; }
diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index df50f599d1a..adfe1835340 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,9 @@
+2019-03-05 Jason Merrill <ja...@redhat.com>
+
+ PR target/88529 - empty class return.
+ * function.c (expand_function_end): Don't copy a TYPE_EMPTY_P
+ result.
+
2019-03-02 Jason Merrill <ja...@redhat.com>
PR c++/86485 - -Wmaybe-unused with empty class ?:
base-commit: 152b1d2a6cb06a70ebfec9af37c134e24f1ba24d
--
2.20.1
