[gcc r12-8294] loongarch: ignore zero-size fields in calling convention

[gcc r12-8294] loongarch: ignore zero-size fields in calling convention

[LuluCheng]

https://gcc.gnu.org/g:d1ee29fd7fb972fee141a0e475f780be4253758a

commit r12-8294-gd1ee29fd7fb972fee141a0e475f780be4253758a
Author: Xi Ruoyao <xry111@mengyan1223.wang>
Date:   Wed Apr 27 19:45:59 2022 +0800

    loongarch: ignore zero-size fields in calling convention
    
    gcc/
    
            * config/loongarch/loongarch.cc
            (loongarch_flatten_aggregate_field): Ignore empty fields for
            RECORD_TYPE.
    
    gcc/testsuite/
    
            * gcc.target/loongarch/zero-size-field-pass.c: New test.
            * gcc.target/loongarch/zero-size-field-ret.c: New test.

Diff:
---
 gcc/config/loongarch/loongarch.cc                  |  3 +++
 .../gcc.target/loongarch/zero-size-field-pass.c    | 30 ++++++++++++++++++++++
 .../gcc.target/loongarch/zero-size-field-ret.c     | 28 ++++++++++++++++++++
 3 files changed, 61 insertions(+)

diff --git a/gcc/config/loongarch/loongarch.cc b/gcc/config/loongarch/loongarch.cc
index f22150a60cc..80046b64006 100644
--- a/gcc/config/loongarch/loongarch.cc
+++ b/gcc/config/loongarch/loongarch.cc
@@ -329,6 +329,9 @@ loongarch_flatten_aggregate_field (const_tree type,
 	    if (!TYPE_P (TREE_TYPE (f)))
 	      return -1;
 
+	    if (DECL_SIZE (f) && integer_zerop (DECL_SIZE (f)))
+	      continue;
+
 	    HOST_WIDE_INT pos = offset + int_byte_position (f);
 	    n = loongarch_flatten_aggregate_field (TREE_TYPE (f), fields, n,
 						   pos);
diff --git a/gcc/testsuite/gcc.target/loongarch/zero-size-field-pass.c b/gcc/testsuite/gcc.target/loongarch/zero-size-field-pass.c
new file mode 100644
index 00000000000..999dc913a71
--- /dev/null
+++ b/gcc/testsuite/gcc.target/loongarch/zero-size-field-pass.c
@@ -0,0 +1,30 @@
+/* Test that LoongArch backend ignores zero-sized fields of aggregates in
+   argument passing.  */
+
+/* { dg-do compile } */
+/* { dg-options "-O2 -mdouble-float -mabi=lp64d" } */
+/* { dg-final { scan-assembler "\\\$f1" } } */
+
+struct test
+{
+  int empty1[0];
+  double empty2[0];
+  int : 0;
+  float x;
+  long empty3[0];
+  long : 0;
+  float y;
+  unsigned : 0;
+  char empty4[0];
+};
+
+extern void callee (struct test);
+
+void
+caller (void)
+{
+  struct test test;
+  test.x = 114;
+  test.y = 514;
+  callee (test);
+}
diff --git a/gcc/testsuite/gcc.target/loongarch/zero-size-field-ret.c b/gcc/testsuite/gcc.target/loongarch/zero-size-field-ret.c
new file mode 100644
index 00000000000..40137d97555
--- /dev/null
+++ b/gcc/testsuite/gcc.target/loongarch/zero-size-field-ret.c
@@ -0,0 +1,28 @@
+/* Test that LoongArch backend ignores zero-sized fields of aggregates in
+   returning.  */
+
+/* { dg-do compile } */
+/* { dg-options "-O2 -mdouble-float -mabi=lp64d" } */
+/* { dg-final { scan-assembler-not "\\\$r4" } } */
+
+struct test
+{
+  int empty1[0];
+  double empty2[0];
+  int : 0;
+  float x;
+  long empty3[0];
+  long : 0;
+  float y;
+  unsigned : 0;
+  char empty4[0];
+};
+
+extern struct test callee (void);
+
+float
+caller (void)
+{
+  struct test test = callee ();
+  return test.x + test.y;
+}