opencode.siil.arti.ee/llvm-tms34010
1
0 Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

[clang] Fix x86_64-windows-msvc over- and under-alignment (#196505)

Browse Source 
This fixes two issues where Clang was both over- and under-aligning
variables:

1) We were applying the x86_64 Sys V psABI "large array" alignment increase
(default when inheriting from X86_64TargetInfo), but MSVC doesn't follow
that ABI.

2) MSVC implements a similar scheme though, where it increases the
alignment of large objects. This is documented for ARM64 [1] and was
implemented in Clang b7c6d95af5, but it
also applies to x86_64. ([2] says "MSVC does size (total size, not
element size) based alignment for global symbols on ARM64 *which is
copied from AMD64*").

This patch stops doing 1) and implements 2) for x86_64-windows-msvc.

[1]
https://learn.microsoft.com/en-us/cpp/build/arm64-windows-abi-conventions?view=msvc-170#alignment
[2] https://github.com/llvm/llvm-project/issues/40851

Fixes https://github.com/llvm/llvm-project/issues/196071
Fixes https://github.com/llvm/llvm-project/issues/171855
This commit is contained in:
Hans Wennborg authored and GitHub committed 2026-05-12 07:55:36 +02:00
1 parent a5d8825fe1
commit 8ecec45518
11 files changed
+60 -28
Download Patch File Download Diff File Expand all files Collapse all files

No files matched your search

clang/include/clang/Basic/TargetInfo.h
+2
View File
@@ -1968,6 +1968,8 @@ private:
void CheckFixedPointBits() const;
};
unsigned Microsoft64BitMinGlobalAlign(uint64_t TypeSize);
namespace targets {
std::unique_ptr<clang::TargetInfo>
AllocateTarget(const llvm::Triple &Triple, const clang::TargetOptions &Opts);
clang/lib/Basic/TargetInfo.cpp
+17
View File
@@ -1114,3 +1114,20 @@ TargetInfo::simplifyConstraint(StringRef Constraint,
}
return Result;
}
unsigned clang::Microsoft64BitMinGlobalAlign(uint64_t TypeSize) {
// MSVC does size based alignment for arm64 based on alignment section in
// below document. Replicate that to keep alignment consistent with object
// files compiled by MSVC.
// https://docs.microsoft.com/en-us/cpp/build/arm64-windows-abi-conventions
// The same is done for x64, but not documented.
if (TypeSize >= 512) // TypeSize >= 64 bytes
return 128; // align type at least 16 bytes
if (TypeSize >= 64) // TypeSize >= 8 bytes
return 64; // align type at least 8 bytes
if (TypeSize >= 16) // TypeSize >= 2 bytes
return 32; // align type at least 4 bytes
return 0;
}
clang/lib/Basic/Targets/AArch64.cpp
+1 -12
View File
@@ -1815,18 +1815,7 @@ unsigned MicrosoftARM64TargetInfo::getMinGlobalAlign(uint64_t TypeSize,
unsigned Align =
WindowsARM64TargetInfo::getMinGlobalAlign(TypeSize, HasNonWeakDef);
// MSVC does size based alignment for arm64 based on alignment section in
// below document, replicate that to keep alignment consistent with object
// files compiled by MSVC.
// https://docs.microsoft.com/en-us/cpp/build/arm64-windows-abi-conventions
if (TypeSize >= 512) { // TypeSize >= 64 bytes
Align = std::max(Align, 128u); // align type at least 16 bytes
} else if (TypeSize >= 64) { // TypeSize >= 8 bytes
Align = std::max(Align, 64u); // align type at least 8 butes
} else if (TypeSize >= 16) { // TypeSize >= 2 bytes
Align = std::max(Align, 32u); // align type at least 4 bytes
}
return Align;
return std::max(Align, Microsoft64BitMinGlobalAlign(TypeSize));
}
MinGWARM64TargetInfo::MinGWARM64TargetInfo(const llvm::Triple &Triple,
clang/lib/Basic/Targets/X86.cpp
+9
View File
@@ -1852,3 +1852,12 @@ X86_64TargetInfo::getTargetBuiltins() const {
"__builtin_ia32_"},
};
}
unsigned
MicrosoftX86_64TargetInfo::getMinGlobalAlign(uint64_t TypeSize,
bool HasNonWeakDef) const {
unsigned Align =
WindowsX86_64TargetInfo::getMinGlobalAlign(TypeSize, HasNonWeakDef);
return std::max(Align, Microsoft64BitMinGlobalAlign(TypeSize));
}
clang/lib/Basic/Targets/X86.h
+5
View File
@@ -968,6 +968,8 @@ public:
: WindowsX86_64TargetInfo(Triple, Opts) {
LongDoubleWidth = LongDoubleAlign = 64;
LongDoubleFormat = &llvm::APFloat::IEEEdouble();
LargeArrayMinWidth = 0;
LargeArrayAlign = 0;
}
void getTargetDefines(const LangOptions &Opts,
@@ -981,6 +983,9 @@ public:
getCallingConvKind(bool ClangABICompat4) const override {
return CCK_MicrosoftWin64;
}
unsigned getMinGlobalAlign(uint64_t TypeSize,
bool HasNonWeakDef) const override;
};
// x86-64 MinGW target
clang/test/CodeGen/align-x68_64.c
+10
View File
@@ -1,11 +1,21 @@
// RUN: %clang_cc1 -triple x86_64-unknown-linux-gnu -emit-llvm %s -o - | FileCheck %s
// RUN: %clang_cc1 -triple x86_64-windows-gnu -emit-llvm %s -o - | FileCheck %s
// RUN: %clang_cc1 -triple x86_64-windows-msvc -emit-llvm %s -o - | FileCheck --check-prefix=MSVC %s
// PR5599
char arr[16];
void test1_f(void *);
void test1_g(void) {
float x[4];
test1_f(x);
}
// CHECK: @arr = {{.*}} align 16
// CHECK: @test1_g
// CHECK: alloca [4 x float], align 16
// The "large array" alignment increase does not apply on windows-msvc.
// MSVC: @arr = {{.*}} align 8
// MSVC: @test1_g
// MSVC: alloca [4 x float], align 4
clang/test/CodeGen/asan-strings.c
+2 -2
View File
@@ -12,6 +12,6 @@ const char *foo(void) { return "asdf"; }
// LINUX: @.str = private unnamed_addr constant [5 x i8] c"asdf\00", align 1
// WINDOWS: @"??_C@_04JIHMPGLA@asdf?$AA@" = linkonce_odr dso_local unnamed_addr constant [5 x i8] c"asdf\00", comdat, align 1
// WINDOWS: @"??_C@_04JIHMPGLA@asdf?$AA@" = linkonce_odr dso_local unnamed_addr constant [5 x i8] c"asdf\00", comdat, align 4
// WINWRITE: @.str = private unnamed_addr global [5 x i8] c"asdf\00", align 1
// WINWRITE: @.str = private unnamed_addr global [5 x i8] c"asdf\00", align 4
clang/test/CodeGen/arm64-microsoft-struct-align.cpp → clang/test/CodeGen/microsoft-64bit-struct-align.cpp
+3 -3
View File
@@ -1,9 +1,9 @@
// RUN: %clang_cc1 -triple aarch64-windows -ffreestanding -emit-llvm -O0 \
// RUN: -x c++ -o - %s | FileCheck %s
// RUN: %clang_cc1 -triple aarch64-windows-msvc -emit-llvm -o - %s | FileCheck %s
// RUN: %clang_cc1 -triple x86_64-windows-msvc -emit-llvm -o - %s | FileCheck %s
struct size1 { char str[1]; };
struct size2 { char str[2]; };
struct size7 { char str[4]; };
struct size7 { char str[7]; };
struct size8 { char str[8]; };
struct size63 { char str[63]; };
struct size64 { char str[64]; };
clang/test/CodeGenCXX/ms-constexpr-static-data-member.cpp
+2 -2
View File
@@ -19,8 +19,8 @@ void usethem() {
useptr(&S::sdm_udt);
}
// CHECK-DAG: @"?sdm_char_array@S@@2QBDB" = linkonce_odr dso_local constant [5 x i8] c"asdf\00", comdat, align 1
// CHECK-DAG: @"?sdm_char_array@S@@2QBDB" = linkonce_odr dso_local constant [5 x i8] c"asdf\00", comdat, align 4
// CHECK-DAG: @"?sdm_char_ptr@S@@2QEBDEB" = linkonce_odr dso_local constant ptr @"??_C@_04JIHMPGLA@asdf?$AA@", comdat, align 8
// CHECK-DAG: @"?sdm_udt@S@@2UFoo@@B" = linkonce_odr dso_local constant %struct.Foo { i32 1, i32 2 }, comdat, align 4
// CHECK-DAG: @"?sdm_udt@S@@2UFoo@@B" = linkonce_odr dso_local constant %struct.Foo { i32 1, i32 2 }, comdat, align 8
clang/test/CodeGenObjC/encode-test-6.m
+1 -1
View File
@@ -80,6 +80,6 @@ const char * Test(void)
// CHECK-DWARF: define{{.*}} ptr @Test()
// CHECK-DWARF: ret ptr @e
// CHECK-MSVC: @e = dso_local global [2 x i8] c"i\00", align 1
// CHECK-MSVC: @e = dso_local global [2 x i8] c"i\00", align 4
// CHECK-MINGW: @e = dso_local global [2 x i8] c"i\00", align 1
// CHECK-ELF: @e = global [2 x i8] c"i\00", align 1
clang/test/CodeGenSYCL/kernel-caller-entry-point.cpp
+8 -8
View File
@@ -148,14 +148,14 @@ int main() {
// CHECK-HOST-LINUX @.str.5 = private unnamed_addr constant [30 x i8] c"_ZTS23fwd_ref_arg_kernel_name\00", align 1
// CHECK-HOST-LINUX: @.str.6 = private unnamed_addr constant [35 x i8] c"_ZTS28fwd_ref_arg_kernel_name_move\00", align 1
// CHECK-HOST-LINUX: @.str.7 = private unnamed_addr constant [33 x i8] c"_ZTS26rvalue_ref_arg_kernel_name\00", align 1
// CHECK-HOST-WINDOWS: @"??_C@_0CB@KFIJOMLB@_ZTS26single_purpose_kernel_name@" = linkonce_odr dso_local unnamed_addr constant [33 x i8] c"_ZTS26single_purpose_kernel_name\00", comdat, align 1
// CHECK-HOST-WINDOWS: @"??_C@_0BC@NHCDOLAA@_ZTSZ4mainEUlT_E_?$AA@" = linkonce_odr dso_local unnamed_addr constant [18 x i8] c"_ZTSZ4mainEUlT_E_\00", comdat, align 1
// CHECK-HOST-WINDOWS: @"??_C@_0M@BCGAEMBE@_ZTS6?N?$LE?O?$IE?O?$IH?$AA@" = linkonce_odr dso_local unnamed_addr constant [12 x i8] c"_ZTS6\CE\B4\CF\84\CF\87\00", comdat, align 1
// CHECK-HOST-WINDOWS: @"??_C@_0P@DLGHPODL@_ZTSZ4mainE2KN?$AA@" = linkonce_odr dso_local unnamed_addr constant [15 x i8] c"_ZTSZ4mainE2KN\00", comdat, align 1
// CHECK-HOST-WINDOWS: @"??_C@_0BK@PPDJPOBM@_ZTS19ref_arg_kernel_name?$AA@" = linkonce_odr dso_local unnamed_addr constant [26 x i8] c"_ZTS19ref_arg_kernel_name\00", comdat, align 1
// CHECK-HOST-WINDOWS: @"??_C@_0BO@KEIBIHKH@_ZTS23fwd_ref_arg_kernel_name?$AA@" = linkonce_odr dso_local unnamed_addr constant [30 x i8] c"_ZTS23fwd_ref_arg_kernel_name\00", comdat, align 1
// CHECK-HOST-WINDOWS: @"??_C@_0CD@FDALJLMM@_ZTS28fwd_ref_arg_kernel_name_mo@" = linkonce_odr dso_local unnamed_addr constant [35 x i8] c"_ZTS28fwd_ref_arg_kernel_name_move\00", comdat, align 1
// CHECK-HOST-WINDOWS: @"??_C@_0CB@HCPMABHM@_ZTS26rvalue_ref_arg_kernel_name@" = linkonce_odr dso_local unnamed_addr constant [33 x i8] c"_ZTS26rvalue_ref_arg_kernel_name\00", comdat, align 1
// CHECK-HOST-WINDOWS: @"??_C@_0CB@KFIJOMLB@_ZTS26single_purpose_kernel_name@" = linkonce_odr dso_local unnamed_addr constant [33 x i8] c"_ZTS26single_purpose_kernel_name\00", comdat
// CHECK-HOST-WINDOWS: @"??_C@_0BC@NHCDOLAA@_ZTSZ4mainEUlT_E_?$AA@" = linkonce_odr dso_local unnamed_addr constant [18 x i8] c"_ZTSZ4mainEUlT_E_\00", comdat
// CHECK-HOST-WINDOWS: @"??_C@_0M@BCGAEMBE@_ZTS6?N?$LE?O?$IE?O?$IH?$AA@" = linkonce_odr dso_local unnamed_addr constant [12 x i8] c"_ZTS6\CE\B4\CF\84\CF\87\00", comdat
// CHECK-HOST-WINDOWS: @"??_C@_0P@DLGHPODL@_ZTSZ4mainE2KN?$AA@" = linkonce_odr dso_local unnamed_addr constant [15 x i8] c"_ZTSZ4mainE2KN\00", comdat
// CHECK-HOST-WINDOWS: @"??_C@_0BK@PPDJPOBM@_ZTS19ref_arg_kernel_name?$AA@" = linkonce_odr dso_local unnamed_addr constant [26 x i8] c"_ZTS19ref_arg_kernel_name\00", comdat
// CHECK-HOST-WINDOWS: @"??_C@_0BO@KEIBIHKH@_ZTS23fwd_ref_arg_kernel_name?$AA@" = linkonce_odr dso_local unnamed_addr constant [30 x i8] c"_ZTS23fwd_ref_arg_kernel_name\00", comdat
// CHECK-HOST-WINDOWS: @"??_C@_0CD@FDALJLMM@_ZTS28fwd_ref_arg_kernel_name_mo@" = linkonce_odr dso_local unnamed_addr constant [35 x i8] c"_ZTS28fwd_ref_arg_kernel_name_move\00", comdat
// CHECK-HOST-WINDOWS: @"??_C@_0CB@HCPMABHM@_ZTS26rvalue_ref_arg_kernel_name@" = linkonce_odr dso_local unnamed_addr constant [33 x i8] c"_ZTS26rvalue_ref_arg_kernel_name\00", comdat
//
// CHECK-HOST-LINUX: define dso_local void @_Z26single_purpose_kernel_task21single_purpose_kernel() #{{[0-9]+}} {
// CHECK-HOST-LINUX-NEXT: entry: