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[AArch64] Match GCC behaviour for zero-size structs #124760

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Merged
merged 4 commits into from
Jan 29, 2025
Merged

[AArch64] Match GCC behaviour for zero-size structs #124760

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a162cee
[AArch64] Fix some misleading comments
ostannard Dec 12, 2024
45fa440
[AArch64] Fix test which wasn't testing anything
ostannard Jan 28, 2025
f1be104
[AArch64] Match GCC behaviour for zero-size structs
ostannard Jan 23, 2025
5a46190
[AArch64] Add tests for variadic functions
ostannard Dec 13, 2024
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13 changes: 8 additions & 5 deletions clang/lib/CodeGen/Targets/AArch64.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -418,18 +418,21 @@ ABIArgInfo AArch64ABIInfo::classifyArgumentType(QualType Ty, bool IsVariadicFn,
CGCXXABI::RAA_DirectInMemory);
}

// Empty records are always ignored on Darwin, but actually passed in C++ mode
// elsewhere for GNU compatibility.
// Empty records:
uint64_t Size = getContext().getTypeSize(Ty);
bool IsEmpty = isEmptyRecord(getContext(), Ty, true);
if (!Ty->isSVESizelessBuiltinType() && (IsEmpty || Size == 0)) {
// Empty records are ignored in C mode, and in C++ on Darwin.
if (!getContext().getLangOpts().CPlusPlus || isDarwinPCS())
return ABIArgInfo::getIgnore();

// GNU C mode. The only argument that gets ignored is an empty one with size
// 0.
if (IsEmpty && Size == 0)
// In C++ mode, arguments which have sizeof() == 0 (which are non-standard
// C++) are ignored. This isn't defined by any standard, so we copy GCC's
// behaviour here.
if (Size == 0)
return ABIArgInfo::getIgnore();

// Otherwise, they are passed as if they have a size of 1 byte.
return ABIArgInfo::getDirect(llvm::Type::getInt8Ty(getVMContext()));
}

Expand Down
85 changes: 65 additions & 20 deletions clang/test/CodeGen/AArch64/args.cpp
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@@ -1,6 +1,6 @@
// RUN: %clang_cc1 -triple arm64-apple-ios7.0 -target-abi darwinpcs -emit-llvm -o - %s | FileCheck %s
// RUN: %clang_cc1 -triple aarch64-linux-gnu -emit-llvm -o - -x c %s | FileCheck %s --check-prefix=CHECK-GNU-C
// RUN: %clang_cc1 -triple aarch64-linux-gnu -emit-llvm -o - %s | FileCheck %s --check-prefix=CHECK-GNU-CXX
// RUN: %clang_cc1 -triple arm64-apple-ios7.0 -target-abi darwinpcs -emit-llvm -o - %s | FileCheck %s --check-prefixes=CHECK,DARWIN
// RUN: %clang_cc1 -triple aarch64-linux-gnu -emit-llvm -o - -x c %s | FileCheck %s --check-prefixes=CHECK,C
// RUN: %clang_cc1 -triple aarch64-linux-gnu -emit-llvm -o - %s | FileCheck %s --check-prefixes=CHECK,CXX

// Empty structs are ignored for PCS purposes on Darwin and in C mode elsewhere.
// In C++ mode on ELF they consume a register slot though. Functions are
Expand All @@ -15,16 +15,16 @@

struct Empty {};

// CHECK: define{{.*}} i32 @empty_arg(i32 noundef %a)
// CHECK-GNU-C: define{{.*}} i32 @empty_arg(i32 noundef %a)
// CHECK-GNU-CXX: define{{.*}} i32 @empty_arg(i8 %e.coerce, i32 noundef %a)
// DARWIN: define{{.*}} i32 @empty_arg(i32 noundef %a)
// C: define{{.*}} i32 @empty_arg(i32 noundef %a)
// CXX: define{{.*}} i32 @empty_arg(i8 %e.coerce, i32 noundef %a)
EXTERNC int empty_arg(struct Empty e, int a) {
return a;
}

// CHECK: define{{.*}} void @empty_ret()
// CHECK-GNU-C: define{{.*}} void @empty_ret()
// CHECK-GNU-CXX: define{{.*}} void @empty_ret()
// DARWIN: define{{.*}} void @empty_ret()
// C: define{{.*}} void @empty_ret()
// CXX: define{{.*}} void @empty_ret()
EXTERNC struct Empty empty_ret(void) {
struct Empty e;
return e;
Expand All @@ -38,30 +38,75 @@ struct SuperEmpty {
int arr[0];
};

// CHECK: define{{.*}} i32 @super_empty_arg(i32 noundef %a)
// CHECK-GNU-C: define{{.*}} i32 @super_empty_arg(i32 noundef %a)
// CHECK-GNU-CXX: define{{.*}} i32 @super_empty_arg(i32 noundef %a)
// DARWIN: define{{.*}} i32 @super_empty_arg(i32 noundef %a)
// C: define{{.*}} i32 @super_empty_arg(i32 noundef %a)
// CXX: define{{.*}} i32 @super_empty_arg(i32 noundef %a)
EXTERNC int super_empty_arg(struct SuperEmpty e, int a) {
return a;
}

// This is not empty. It has 0 size but consumes a register slot for GCC.
// This is also not empty, and non-standard. We previously considered it to
// consume a register slot, but GCC does not, so we match that.

struct SortOfEmpty {
struct SuperEmpty e;
};

// CHECK: define{{.*}} i32 @sort_of_empty_arg(i32 noundef %a)
// CHECK-GNU-C: define{{.*}} i32 @sort_of_empty_arg(i32 noundef %a)
// CHECK-GNU-CXX: define{{.*}} i32 @sort_of_empty_arg(i8 %e.coerce, i32 noundef %a)
EXTERNC int sort_of_empty_arg(struct Empty e, int a) {
// DARWIN: define{{.*}} i32 @sort_of_empty_arg(i32 noundef %a)
// C: define{{.*}} i32 @sort_of_empty_arg(i32 noundef %a)
// CXX: define{{.*}} i32 @sort_of_empty_arg(i32 noundef %a)
EXTERNC int sort_of_empty_arg(struct SortOfEmpty e, int a) {
return a;
}

// CHECK: define{{.*}} void @sort_of_empty_ret()
// CHECK-GNU-C: define{{.*}} void @sort_of_empty_ret()
// CHECK-GNU-CXX: define{{.*}} void @sort_of_empty_ret()
// DARWIN: define{{.*}} void @sort_of_empty_ret()
// C: define{{.*}} void @sort_of_empty_ret()
// CXX: define{{.*}} void @sort_of_empty_ret()
EXTERNC struct SortOfEmpty sort_of_empty_ret(void) {
struct SortOfEmpty e;
return e;
}

#include <stdarg.h>

// va_arg matches the above rules, consuming an incoming argument in cases
// where one would be passed, and not doing so when the argument should be
// ignored.

EXTERNC struct Empty empty_arg_variadic(int a, ...) {
// CHECK-LABEL: @empty_arg_variadic(
// DARWIN-NOT: {{ getelementptr }}
// C-NOT: {{ getelementptr }}
// CXX: %new_reg_offs = add i32 %gr_offs, 8
// CXX: %new_stack = getelementptr inbounds i8, ptr %stack, i64 8
va_list vl;
va_start(vl, a);
struct Empty b = va_arg(vl, struct Empty);
va_end(vl);
return b;
}

EXTERNC struct SuperEmpty super_empty_arg_variadic(int a, ...) {
// CHECK-LABEL: @super_empty_arg_variadic(
// DARWIN-NOT: {{ getelementptr }}
// C-NOT: {{ getelementptr }}
// CXX-NOT: {{ getelementptr }}
va_list vl;
va_start(vl, a);
struct SuperEmpty b = va_arg(vl, struct SuperEmpty);
va_end(vl);
return b;
}

EXTERNC struct SortOfEmpty sort_of_empty_arg_variadic(int a, ...) {
// CHECK-LABEL: @sort_of_empty_arg_variadic(
// DARWIN: %argp.next = getelementptr inbounds i8, ptr %argp.cur, i64 0
// C-NOT: {{ getelementptr }}
// CXX-NOT: {{ getelementptr }}
va_list vl;
va_start(vl, a);
struct SortOfEmpty b = va_arg(vl, struct SortOfEmpty);
va_end(vl);
return b;
}