[clang][test][LoongArch] Pre-commit test for empty struct in C++ mode

[wangleiat]

Summary

This is a preliminary patch that adds test cases for handling empty
structs in C++.

The current implementation for passing empty structs is inconsistent
with the calling convention description. For example, when there is only
one empty struct (it satisfies the condition 0 < WOA < GRLEN),
according to the calling convention, it should be passed through a
GAR (if exists). However, the current implementation does not pass it.
Upcoming patch will address these inconsistencies.

clang/test/CodeGenCXX/LoongArch/abi-lp64d-empty-struct.cpp

+// NOTE: Assertions have been autogenerated by utils/update_cc_test_checks.py UTC_ARGS: --filter "^define" --version 2
+// RUN: %clang_cc1 -triple loongarch64 -target-feature +f -target-feature +d -target-abi lp64d \
+// RUN:   -emit-llvm %s -o - | FileCheck %s
+
+/// Treat the empty struct as char in C++ mode (sizeof(empty_s) = 1).
+/// If the empty struct is a struct's member, will be treated as
+/// fixed-point member.
+/// WOA: Bit width of the argument.
+/// FIXME: Empty struct is always passed or returned in C++ mode.
+
+/// 1. 0 < WOA <= GRLEN
+/// 1.a. Only fixed-point members.
+
+struct empty_s {};
+// CHECK-LABEL: define dso_local void @_Z12empty_struct7empty_s
+// CHECK-SAME: () #[[ATTR0:[0-9]+]] {
+struct empty_s empty_struct(struct empty_s e) {
+  return e;
+}
+
+struct empty_char_s {
+  struct empty_s e;
+  char c;
+};
+// CHECK-LABEL: define dso_local i64 @_Z18empty_float_struct12empty_char_s
+// CHECK-SAME: (i64 [[S_COERCE:%.*]]) #[[ATTR0:[0-9]+]] {
+struct empty_char_s empty_float_struct(struct empty_char_s s) {
+  return s;
+}
+
+/// 1.b. Only floating-point members.
+/// Nothing to do. The empty struct treated as fixed-point member.
+
+/// 1.c. Both fixed-point and floating-point members.
+/// 1.c.i. Multiple fixed-point members.
+
+struct empty_char_float_s {
+  struct empty_s e1;
+  char c;
+  float f32;
+};
+// CHECK-LABEL: define dso_local { i8, float } @_Z23empty_char_float_struct18empty_char_float_s
+// CHECK-SAME: (i8 [[TMP0:%.*]], float [[TMP1:%.*]]) #[[ATTR0:[0-9]+]] {
+struct empty_char_float_s empty_char_float_struct(struct empty_char_float_s s) {
+  return s;
+}
+
+/// 1.c.ii. One fixed-point member.
+
+struct empty_float_s {
+  struct empty_s e;
+  float f32;
+};
+// CHECK-LABEL: define dso_local float @_Z18empty_float_struct13empty_float_s
+// CHECK-SAME: (float [[TMP0:%.*]]) #[[ATTR0:[0-9]+]] {
+struct empty_float_s empty_float_struct(struct empty_float_s s) {
+  return s;
+}
+
+struct float_empty_s {
+  float f32;
+  struct empty_s e;
+};
+
+// CHECK-LABEL: define dso_local float @_Z18float_empty_struct13float_empty_s
+// CHECK-SAME: (float [[TMP0:%.*]]) #[[ATTR0:[0-9]+]] {
+struct float_empty_s float_empty_struct(struct float_empty_s s) {
+  return s;
+}
+
+/// 2. GRLEN < WOA <= 2*GRLEN
+
+/// 2.a. Only fixed-point members.
+struct empty_long_s {
+  struct empty_s e;
+  long l;
+};
+// CHECK-LABEL: define dso_local [2 x i64] @_Z17empty_long_struct12empty_long_s
+// CHECK-SAME: ([2 x i64] [[S_COERCE:%.*]]) #[[ATTR0:[0-9]+]] {
+struct empty_long_s empty_long_struct(struct empty_long_s s) {
+  return s;
+}
+
+/// 2.b. Only floating-point members.
+/// Nothing to do.
+
+/// 2.c. Both fixed-point and floating-point members.
+/// 2.c.i. The structure has one floating-point member and only one fixed-point
+/// member.
+
+struct empty_double_s {
+  struct empty_s e;
+  double f64;
+};
+// CHECK-LABEL: define dso_local double @_Z19empty_double_struct14empty_double_s
+// CHECK-SAME: (double [[TMP0:%.*]]) #[[ATTR0:[0-9]+]] {
+struct empty_double_s empty_double_struct(struct empty_double_s s) {
+  return s;
+}
+
+struct double_empty_s {
+  double f64;
+  struct empty_s e;
+};
+// CHECK-LABEL: define dso_local double @_Z19double_empty_struct14double_empty_s
+// CHECK-SAME: (double [[TMP0:%.*]]) #[[ATTR0:[0-9]+]] {
+struct double_empty_s double_empty_struct(struct double_empty_s s) {
+  return s;
+}
+
+/// 2.c.ii. Others
+
+struct empty_float_char_s {
+  struct empty_s e1;
+  float f32;
+  char c;
+};
+// CHECK-LABEL: define dso_local { float, i8 } @_Z23empty_float_char_struct18empty_float_char_s
+// CHECK-SAME: (float [[TMP0:%.*]], i8 [[TMP1:%.*]]) #[[ATTR0:[0-9]+]] {
+struct empty_float_char_s empty_float_char_struct(struct empty_float_char_s s) {
+  return s;
+}
+
+struct empty_float_double_s {
+  struct empty_s e1;
+  float f32;
+  double f64;
+};
+// CHECK-LABEL: define dso_local { float, double } @_Z25empty_float_double_struct20empty_float_double_s
+// CHECK-SAME: (float [[TMP0:%.*]], double [[TMP1:%.*]]) #[[ATTR0:[0-9]+]] {
+struct empty_float_double_s empty_float_double_struct(struct empty_float_double_s s) {
+  return s;
+}
+
+/// 3 WOA > 2*GRLEN
+
+struct empty_long_empty_s {
+  struct empty_s e1;
+  long l;
+  struct empty_s e2;
+};
+// CHECK-LABEL: define dso_local void @_Z23empty_long_empty_struct18empty_long_empty_s
+// CHECK-SAME: (ptr noalias sret([[STRUCT_EMPTY_LONG_EMPTY_S:%.*]]) align 8 [[AGG_RESULT:%.*]], ptr noundef [[S:%.*]]) #[[ATTR0:[0-9]+]] {
+struct empty_long_empty_s empty_long_empty_struct(struct empty_long_empty_s s) {
+  return s;
+}
+
+struct empty_double_empty_s {
+  struct empty_s e1;
+  double f64;
+  struct empty_s e2;
+};
+// CHECK-LABEL: define dso_local double @_Z25empty_double_empty_struct20empty_double_empty_s
+// CHECK-SAME: (double [[TMP0:%.*]]) #[[ATTR0:[0-9]+]] {
+struct empty_double_empty_s empty_double_empty_struct(struct empty_double_empty_s s) {
+  return s;
+}