[LoongArch] Fix ABI mismatch with g++ when handling empty unions #71025
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In g++, empty unions are not ignored like empty structs when flattening structs to examine whether the structs can be passed via FARs in C++. This patch aligns clang++ with g++. Fix llvm#70890.
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@llvm/pr-subscribers-clang-codegen @llvm/pr-subscribers-clang Author: Lu Weining (SixWeining) ChangesIn g++, empty unions are not ignored like empty structs when flattening structs to examine whether the structs can be passed via FARs in C++. This patch aligns clang++ with g++. Fix #70890. Full diff: https://github.com/llvm/llvm-project/pull/71025.diff 3 Files Affected:
diff --git a/clang/lib/CodeGen/Targets/LoongArch.cpp b/clang/lib/CodeGen/Targets/LoongArch.cpp
index c4d886eb40725f8..7b2c31139b0b2a3 100644
--- a/clang/lib/CodeGen/Targets/LoongArch.cpp
+++ b/clang/lib/CodeGen/Targets/LoongArch.cpp
@@ -170,10 +170,11 @@ bool LoongArchABIInfo::detectFARsEligibleStructHelper(
// copy constructor are not eligible for the FP calling convention.
if (getRecordArgABI(Ty, CGT.getCXXABI()))
return false;
- 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).
+ if (isEmptyRecord(getContext(), Ty, true, true) &&
+ (!RD->isUnion() || !isa<CXXRecordDecl>(RD)))
+ return true;
+ // Unions aren't eligible unless they're empty in C (which is caught above).
if (RD->isUnion())
return false;
const ASTRecordLayout &Layout = getContext().getASTRecordLayout(RD);
diff --git a/clang/test/CodeGen/LoongArch/abi-lp64d-empty-structs.c b/clang/test/CodeGen/LoongArch/abi-lp64d-empty-structs.c
index 281b7b15841a999..2f7596f0ebdc8be 100644
--- a/clang/test/CodeGen/LoongArch/abi-lp64d-empty-structs.c
+++ b/clang/test/CodeGen/LoongArch/abi-lp64d-empty-structs.c
@@ -3,7 +3,7 @@
// 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
-// Fields containing empty structs or unions are ignored when flattening
+// Fields containing empty structs 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
// not ignored in C++. These rules are not documented in psABI <https://www.github.com/loongson/la-abi-specs>
diff --git a/clang/test/CodeGen/LoongArch/abi-lp64d-empty-unions.c b/clang/test/CodeGen/LoongArch/abi-lp64d-empty-unions.c
index b0607425336e285..363e37efb64691e 100644
--- a/clang/test/CodeGen/LoongArch/abi-lp64d-empty-unions.c
+++ b/clang/test/CodeGen/LoongArch/abi-lp64d-empty-unions.c
@@ -19,8 +19,7 @@ struct s1 {
};
// CHECK-C: define{{.*}} { i32, float } @test2(i32{{[^,]*}}, float{{[^,]*}})
-/// FIXME: This doesn't match g++.
-// CHECK-CXX: define{{.*}} { i32, float } @_Z5test22s1(i32{{[^,]*}}, float{{[^,]*}})
+// CHECK-CXX: define{{.*}} [2 x i64] @_Z5test22s1([2 x i64]{{[^,]*}})
struct s1 test2(struct s1 a) {
return a;
}
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@llvm/pr-subscribers-backend-loongarch Author: Lu Weining (SixWeining) ChangesIn g++, empty unions are not ignored like empty structs when flattening structs to examine whether the structs can be passed via FARs in C++. This patch aligns clang++ with g++. Fix #70890. Full diff: https://github.com/llvm/llvm-project/pull/71025.diff 3 Files Affected:
diff --git a/clang/lib/CodeGen/Targets/LoongArch.cpp b/clang/lib/CodeGen/Targets/LoongArch.cpp
index c4d886eb40725f8..7b2c31139b0b2a3 100644
--- a/clang/lib/CodeGen/Targets/LoongArch.cpp
+++ b/clang/lib/CodeGen/Targets/LoongArch.cpp
@@ -170,10 +170,11 @@ bool LoongArchABIInfo::detectFARsEligibleStructHelper(
// copy constructor are not eligible for the FP calling convention.
if (getRecordArgABI(Ty, CGT.getCXXABI()))
return false;
- 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).
+ if (isEmptyRecord(getContext(), Ty, true, true) &&
+ (!RD->isUnion() || !isa<CXXRecordDecl>(RD)))
+ return true;
+ // Unions aren't eligible unless they're empty in C (which is caught above).
if (RD->isUnion())
return false;
const ASTRecordLayout &Layout = getContext().getASTRecordLayout(RD);
diff --git a/clang/test/CodeGen/LoongArch/abi-lp64d-empty-structs.c b/clang/test/CodeGen/LoongArch/abi-lp64d-empty-structs.c
index 281b7b15841a999..2f7596f0ebdc8be 100644
--- a/clang/test/CodeGen/LoongArch/abi-lp64d-empty-structs.c
+++ b/clang/test/CodeGen/LoongArch/abi-lp64d-empty-structs.c
@@ -3,7 +3,7 @@
// 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
-// Fields containing empty structs or unions are ignored when flattening
+// Fields containing empty structs 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
// not ignored in C++. These rules are not documented in psABI <https://www.github.com/loongson/la-abi-specs>
diff --git a/clang/test/CodeGen/LoongArch/abi-lp64d-empty-unions.c b/clang/test/CodeGen/LoongArch/abi-lp64d-empty-unions.c
index b0607425336e285..363e37efb64691e 100644
--- a/clang/test/CodeGen/LoongArch/abi-lp64d-empty-unions.c
+++ b/clang/test/CodeGen/LoongArch/abi-lp64d-empty-unions.c
@@ -19,8 +19,7 @@ struct s1 {
};
// CHECK-C: define{{.*}} { i32, float } @test2(i32{{[^,]*}}, float{{[^,]*}})
-/// FIXME: This doesn't match g++.
-// CHECK-CXX: define{{.*}} { i32, float } @_Z5test22s1(i32{{[^,]*}}, float{{[^,]*}})
+// CHECK-CXX: define{{.*}} [2 x i64] @_Z5test22s1([2 x i64]{{[^,]*}})
struct s1 test2(struct s1 a) {
return a;
}
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heiher
approved these changes
Nov 3, 2023
leecheechen
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Jun 9, 2025
…m#71025) In g++, empty unions are not ignored like empty structs when flattening structs to examine whether the structs can be passed via FARs in C++. This patch aligns clang++ with g++. Fix llvm#70890. (cherry picked from commit 4253fdc) Change-Id: Ib9b0cc6e74f8e52ff394fc53b7fc9f4602d64096
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In g++, empty unions are not ignored like empty structs when flattening structs to examine whether the structs can be passed via FARs in C++. This patch aligns clang++ with g++.
Fix #70890.