[PATCH] D156116: [Clang][LoongArch] Fix ABI handling of empty structs in C++ to match GCC behaviour

[Lu Weining via Phabricator via cfe-commits]

This revision was landed with ongoing or failed builds.
This revision was automatically updated to reflect the committed changes.
Closed by commit rGc299efbf284f: [Clang][LoongArch] Fix ABI handling of empty structs in C++ to match GCC… (authored by SixWeining).

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D156116/new/

https://reviews.llvm.org/D156116

Files:
  clang/docs/ReleaseNotes.rst
  clang/lib/CodeGen/Targets/LoongArch.cpp
  clang/test/CodeGen/LoongArch/abi-lp64d-empty-structs.c


Index: clang/test/CodeGen/LoongArch/abi-lp64d-empty-structs.c
===================================================================
--- clang/test/CodeGen/LoongArch/abi-lp64d-empty-structs.c
+++ clang/test/CodeGen/LoongArch/abi-lp64d-empty-structs.c
@@ -3,7 +3,6 @@
 // RUN: %clang_cc1 -triple loongarch64 -target-feature +f -target-feature +d -target-abi lp64d -emit-llvm %s -o - -x c++ | \
 // RUN:   FileCheck --check-prefix=CHECK-CXX %s
 
-// FIXME: This isn't currently respected.
 // Fields containing empty structs or unions are ignored when flattening
 // structs to examine whether the structs can be passed via FARs, even in C++.
 // But there is an exception that non-zero-length array of empty structures are
@@ -16,7 +15,7 @@
 struct s1 { struct empty e; float f; };
 
 // CHECK-C: define{{.*}} float @test_s1(float {{.*}})
-// CHECK-CXX: define{{.*}} i64 @_Z7test_s12s1(i64 {{.*}})
+// CHECK-CXX: define{{.*}} float @_Z7test_s12s1(float {{.*}})
 struct s1 test_s1(struct s1 a) {
   return a;
 }
@@ -24,7 +23,7 @@
 struct s2 { struct empty e; int32_t i; float f; };
 
 // CHECK-C: define{{.*}} { i32, float } @test_s2(i32 {{.*}}, float {{.*}})
-// CHECK-CXX: define{{.*}} [2 x i64] @_Z7test_s22s2([2 x i64] {{.*}})
+// CHECK-CXX: define{{.*}} { i32, float } @_Z7test_s22s2(i32 {{.*}}, float {{.*}})
 struct s2 test_s2(struct s2 a) {
   return a;
 }
@@ -32,7 +31,7 @@
 struct s3 { struct empty e; float f; float g; };
 
 // CHECK-C: define{{.*}} { float, float } @test_s3(float {{.*}}, float {{.*}})
-// CHECK-CXX: define{{.*}} [2 x i64] @_Z7test_s32s3([2 x i64] {{.*}})
+// CHECK-CXX: define{{.*}} { float, float } @_Z7test_s32s3(float {{.*}}, float {{.*}})
 struct s3 test_s3(struct s3 a) {
   return a;
 }
@@ -40,7 +39,7 @@
 struct s4 { struct empty e; float __complex__ c; };
 
 // CHECK-C: define{{.*}} { float, float } @test_s4(float {{.*}}, float {{.*}})
-// CHECK-CXX: define{{.*}} [2 x i64] @_Z7test_s42s4([2 x i64] {{.*}})
+// CHECK-CXX: define{{.*}} { float, float } @_Z7test_s42s4(float {{.*}}, float {{.*}})
 struct s4 test_s4(struct s4 a) {
   return a;
 }
@@ -77,7 +76,7 @@
 struct s8 { struct empty_arr0 e; float f; };
 
 // CHECK-C: define{{.*}} float @test_s8(float {{.*}})
-// CHECK-CXX: define{{.*}} i64 @_Z7test_s82s8(i64 {{.*}})
+// CHECK-CXX: define{{.*}} float @_Z7test_s82s8(float {{.*}})
 struct s8 test_s8(struct s8 a) {
   return a;
 }
Index: clang/lib/CodeGen/Targets/LoongArch.cpp
===================================================================
--- clang/lib/CodeGen/Targets/LoongArch.cpp
+++ clang/lib/CodeGen/Targets/LoongArch.cpp
@@ -148,6 +148,13 @@
   if (const ConstantArrayType *ATy = getContext().getAsConstantArrayType(Ty)) {
     uint64_t ArraySize = ATy->getSize().getZExtValue();
     QualType EltTy = ATy->getElementType();
+    // Non-zero-length arrays of empty records make the struct ineligible to be
+    // passed via FARs in C++.
+    if (const auto *RTy = EltTy->getAs<RecordType>()) {
+      if (ArraySize != 0 && isa<CXXRecordDecl>(RTy->getDecl()) &&
+          isEmptyRecord(getContext(), EltTy, true, true))
+        return false;
+    }
     CharUnits EltSize = getContext().getTypeSizeInChars(EltTy);
     for (uint64_t i = 0; i < ArraySize; ++i) {
       if (!detectFARsEligibleStructHelper(EltTy, CurOff, Field1Ty, Field1Off,
@@ -163,7 +170,7 @@
     // copy constructor are not eligible for the FP calling convention.
     if (getRecordArgABI(Ty, CGT.getCXXABI()))
       return false;
-    if (isEmptyRecord(getContext(), Ty, true))
+    if (isEmptyRecord(getContext(), Ty, true, true))
       return true;
     const RecordDecl *RD = RTy->getDecl();
     // Unions aren't eligible unless they're empty (which is caught above).
Index: clang/docs/ReleaseNotes.rst
===================================================================
--- clang/docs/ReleaseNotes.rst
+++ clang/docs/ReleaseNotes.rst
@@ -891,6 +891,8 @@
   on LoongArch.
 - Unaligned memory accesses can be toggled by ``-m[no-]unaligned-access`` or the
   aliases ``-m[no-]strict-align``.
+- An ABI mismatch between GCC and Clang related to the handling of empty structs
+  in C++ parameter passing under ``lp64d`` ABI was fixed.
 
 RISC-V Support
 ^^^^^^^^^^^^^^


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