Skip to content

Driver, CodeGen: Handle -falign-functions, -fno-align-functions and -falign-functions=1 correctly. #149445

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
wants to merge 2 commits into
base: users/pcc/spr/main.driver-codegen-handle-falign-functions-fno-align-functions-and-falign-functions1-correctly
Choose a base branch
from
Open

Driver, CodeGen: Handle -falign-functions, -fno-align-functions and -falign-functions=1 correctly. #149445

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
2 commits
Select commit Hold shift + click to select a range
dc3d07d
[𝘀𝗽𝗿] initial version
pcc Jul 18, 2025
99a4bcd
Omit flag if 0
pcc Jul 18, 2025
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
4 changes: 2 additions & 2 deletions clang/include/clang/Driver/CommonArgs.h
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -85,8 +85,8 @@ const char *RelocationModelName(llvm::Reloc::Model Model);
std::tuple<llvm::Reloc::Model, unsigned, bool>
ParsePICArgs(const ToolChain &ToolChain, const llvm::opt::ArgList &Args);

unsigned ParseFunctionAlignment(const ToolChain &TC,
const llvm::opt::ArgList &Args);
llvm::MaybeAlign ParseFunctionAlignment(const ToolChain &TC,
const llvm::opt::ArgList &Args);

void addDebugInfoKind(llvm::opt::ArgStringList &CmdArgs,
llvm::codegenoptions::DebugInfoKind DebugInfoKind);
Expand Down
8 changes: 5 additions & 3 deletions clang/lib/CodeGen/CodeGenModule.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -2760,9 +2760,11 @@ void CodeGenModule::SetLLVMFunctionAttributesForDefinition(const Decl *D,
if (alignment)
F->setAlignment(llvm::Align(alignment));

if (!D->hasAttr<AlignedAttr>())
if (LangOpts.FunctionAlignment)
F->setAlignment(llvm::Align(1ull << LangOpts.FunctionAlignment));
if (!D->hasAttr<AlignedAttr>()) {
llvm::MaybeAlign Align = llvm::decodeMaybeAlign(LangOpts.FunctionAlignment);
if (Align)
F->setAlignment(*Align);
}

// Some C++ ABIs require 2-byte alignment for member functions, in order to
// reserve a bit for differentiating between virtual and non-virtual member
Expand Down
7 changes: 4 additions & 3 deletions clang/lib/Driver/ToolChains/Clang.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -40,6 +40,7 @@
#include "llvm/Frontend/Debug/Options.h"
#include "llvm/Object/ObjectFile.h"
#include "llvm/Option/ArgList.h"
#include "llvm/Support/Alignment.h"
#include "llvm/Support/CodeGen.h"
#include "llvm/Support/Compiler.h"
#include "llvm/Support/Compression.h"
Expand Down Expand Up @@ -5516,11 +5517,11 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,

CheckCodeGenerationOptions(D, Args);

unsigned FunctionAlignment = ParseFunctionAlignment(TC, Args);
assert(FunctionAlignment <= 31 && "function alignment will be truncated!");
llvm::MaybeAlign FunctionAlignment = ParseFunctionAlignment(TC, Args);
if (FunctionAlignment) {
CmdArgs.push_back("-function-alignment");
CmdArgs.push_back(Args.MakeArgString(std::to_string(FunctionAlignment)));
CmdArgs.push_back(
Args.MakeArgString(std::to_string(llvm::encode(FunctionAlignment))));
}

// We support -falign-loops=N where N is a power of 2. GCC supports more
Expand Down
20 changes: 12 additions & 8 deletions clang/lib/Driver/ToolChains/CommonArgs.cpp
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -2120,29 +2120,33 @@ tools::ParsePICArgs(const ToolChain &ToolChain, const ArgList &Args) {
// [0, 65536]. If the value is not a power-of-two, it will be rounded up to
// the nearest power-of-two.
//
// If we return `0`, the frontend will default to the backend's preferred
// alignment.
// If we return `MaybeAlign()`, the frontend will default to the backend's
// preferred alignment.
//
// NOTE: icc only allows values between [0, 4096]. icc uses `-falign-functions`
// to mean `-falign-functions=16`. GCC defaults to the backend's preferred
// alignment. For unaligned functions, we default to the backend's preferred
// alignment.
unsigned tools::ParseFunctionAlignment(const ToolChain &TC,
const ArgList &Args) {
llvm::MaybeAlign tools::ParseFunctionAlignment(const ToolChain &TC,
const ArgList &Args) {
const Arg *A = Args.getLastArg(options::OPT_falign_functions,
options::OPT_falign_functions_EQ,
options::OPT_fno_align_functions);
if (!A || A->getOption().matches(options::OPT_fno_align_functions))
return 0;
if (!A)
return llvm::MaybeAlign();

if (A->getOption().matches(options::OPT_fno_align_functions))
return llvm::Align(1);

if (A->getOption().matches(options::OPT_falign_functions))
return 0;
return llvm::MaybeAlign();

unsigned Value = 0;
if (StringRef(A->getValue()).getAsInteger(10, Value) || Value > 65536)
TC.getDriver().Diag(diag::err_drv_invalid_int_value)
<< A->getAsString(Args) << A->getValue();
return Value ? llvm::Log2_32_Ceil(std::min(Value, 65536u)) : Value;
return Value ? llvm::Align(1 << llvm::Log2_32_Ceil(std::min(Value, 65536u)))
: llvm::MaybeAlign();
}

void tools::addDebugInfoKind(
Expand Down
10 changes: 7 additions & 3 deletions clang/test/CodeGen/function-alignment.c
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -1,13 +1,17 @@
// RUN: %clang_cc1 -emit-llvm %s -o - | FileCheck %s -check-prefix CHECK-NONE
// RUN: %clang_cc1 -emit-llvm -function-alignment 4 %s -o - | FileCheck %s -check-prefix CHECK-16
// RUN: %clang_cc1 -emit-llvm -function-alignment 5 %s -o - | FileCheck %s -check-prefix CHECK-32
// RUN: %clang_cc1 -emit-llvm -function-alignment 0 %s -o - | FileCheck %s -check-prefix CHECK-NONE
// RUN: %clang_cc1 -emit-llvm -function-alignment 1 %s -o - | FileCheck %s -check-prefix CHECK-1
// RUN: %clang_cc1 -emit-llvm -function-alignment 5 %s -o - | FileCheck %s -check-prefix CHECK-16
// RUN: %clang_cc1 -emit-llvm -function-alignment 6 %s -o - | FileCheck %s -check-prefix CHECK-32

void f(void) {}
void __attribute__((__aligned__(64))) g(void) {}

// CHECK-NONE-NOT: define {{(dso_local )?}}void @f() #0 align
// CHECK-NONE: define {{(dso_local )?}}void @g() #0 align 64

// CHECK-1: define {{(dso_local )?}}void @f() #0 align 1
// CHECK-1: define {{(dso_local )?}}void @g() #0 align 64

// CHECK-16: define {{(dso_local )?}}void @f() #0 align 16
// CHECK-16: define {{(dso_local )?}}void @g() #0 align 64

Expand Down
12 changes: 6 additions & 6 deletions clang/test/Driver/function-alignment.c
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -1,17 +1,17 @@
// RUN: %clang -### %s 2>&1 | FileCheck %s -check-prefix CHECK-0
// RUN: %clang -### -falign-functions %s 2>&1 | FileCheck %s -check-prefix CHECK-1
// RUN: %clang -### -falign-functions %s 2>&1 | FileCheck %s -check-prefix CHECK-0
// RUN: %clang -### -fno-align-functions %s 2>&1 | FileCheck %s -check-prefix CHECK-1
// RUN: %clang -### -falign-functions=1 %s 2>&1 | FileCheck %s -check-prefix CHECK-1
// RUN: %clang -### -falign-functions=2 %s 2>&1 | FileCheck %s -check-prefix CHECK-2
// RUN: %clang -### -falign-functions=3 %s 2>&1 | FileCheck %s -check-prefix CHECK-3
// RUN: %clang -### -falign-functions=4 %s 2>&1 | FileCheck %s -check-prefix CHECK-4
// RUN: %clang -### -falign-functions=4 %s 2>&1 | FileCheck %s -check-prefix CHECK-3
// RUN: not %clang -### -falign-functions=65537 %s 2>&1 | FileCheck %s -check-prefix CHECK-ERR-65537
// RUN: not %clang -### -falign-functions=a %s 2>&1 | FileCheck %s -check-prefix CHECK-ERR-A

// CHECK-0-NOT: "-function-alignment"
// CHECK-1-NOT: "-function-alignment"
// CHECK-2: "-function-alignment" "1"
// CHECK-3: "-function-alignment" "2"
// CHECK-4: "-function-alignment" "2"
// CHECK-1: "-function-alignment" "1"
// CHECK-2: "-function-alignment" "2"
// CHECK-3: "-function-alignment" "3"
// CHECK-ERR-65537: error: invalid integral value '65537' in '-falign-functions=65537'
// CHECK-ERR-A: error: invalid integral value 'a' in '-falign-functions=a'

Loading