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[X86][clang-cl] Add CL option /vlen #166375

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Merged
phoebewang merged 3 commits into from
Nov 8, 2025
Merged

[X86][clang-cl] Add CL option /vlen #166375

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bdecf07
[X86][clang-cl] Add CL option /arch
phoebewang Nov 4, 2025
266f047
Address review comments
phoebewang Nov 7, 2025
83d24bd
Address review comment
phoebewang Nov 7, 2025
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3 changes: 3 additions & 0 deletions clang/include/clang/Basic/DiagnosticDriverKinds.td
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Expand Up @@ -207,6 +207,9 @@ def err_drv_amdgpu_ieee_without_no_honor_nans : Error<
"invalid argument '-mno-amdgpu-ieee' only allowed with relaxed NaN handling">;
def err_drv_argument_not_allowed_with : Error<
"invalid argument '%0' not allowed with '%1'">;
def warn_drv_argument_not_allowed_with : Warning<
"invalid argument '%0' not allowed with '%1'">,
InGroup<OptionIgnored>;
def err_drv_cannot_open_randomize_layout_seed_file : Error<
"cannot read randomize layout seed file '%0'">;
def err_drv_invalid_version_number : Error<
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6 changes: 6 additions & 0 deletions clang/include/clang/Driver/Options.td
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Expand Up @@ -9218,6 +9218,12 @@ def : CLFlag<"Qscatter-">, Alias<mno_scatter>,

def _SLASH_arch : CLCompileJoined<"arch:">,
HelpText<"Set architecture for code generation">;
def _SLASH_vlen : CLFlag<"vlen">,
HelpText<"Set default vector length for autovectorization and other optimizations">;
def _SLASH_vlen_EQ_256 : CLFlag<"vlen=256">,
HelpText<"Set vector length of 256 bits for autovectorization and other optimizations">;
def _SLASH_vlen_EQ_512 : CLFlag<"vlen=512">,
HelpText<"Set vector length of 512 bits for autovectorization and other optimizations">;

def _SLASH_M_Group : OptionGroup<"</M group>">, Group<cl_compile_Group>;
def _SLASH_volatile_Group : OptionGroup<"</volatile group>">,
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25 changes: 25 additions & 0 deletions clang/lib/Driver/ToolChains/Clang.cpp
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Expand Up @@ -8266,6 +8266,31 @@ void Clang::AddClangCLArgs(const ArgList &Args, types::ID InputType,
<< "/kernel";
}

if (const Arg *A = Args.getLastArg(options::OPT__SLASH_vlen,
options::OPT__SLASH_vlen_EQ_256,
options::OPT__SLASH_vlen_EQ_512)) {
llvm::SmallSet<std::string, 4> Arch512 = {"AVX512F", "AVX512"};
llvm::SmallSet<std::string, 4> Arch256 = {"AVX", "AVX2"};

StringRef Arch = Args.getLastArgValue(options::OPT__SLASH_arch);
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@zmodem zmodem Nov 7, 2025

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What if the user didn't pass /arch?
What if they passed -mavx512?

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@phoebewang phoebewang Nov 7, 2025

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Good question. MSVC has a default value for /arch. We should match it here. -mavx512xxx is a single feature, which is orthogonal to /arch. We don't need to check them.


if (A->getOption().matches(options::OPT__SLASH_vlen_EQ_512)) {
if (Arch512.contains(Arch.str()))
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@zmodem zmodem Nov 7, 2025

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Since the set is so small, and only used here, I think just open-coding the logic would be easier:

if (Arch == "AVX512" || Arch == "AVX512F")

Same for the Arch256 set below.

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@phoebewang phoebewang Nov 7, 2025

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We will add AVX10.1, AVX10.2 soon, but I can change it for now.

CmdArgs.push_back("-mprefer-vector-width=512");
else
D.Diag(diag::warn_drv_argument_not_allowed_with)
<< "/vlen=512" << std::string("/arch:").append(Arch);
}

if (A->getOption().matches(options::OPT__SLASH_vlen_EQ_256)) {
if (Arch512.contains(Arch.str()))
CmdArgs.push_back("-mprefer-vector-width=256");
else if (!Arch256.contains(Arch.str()))
D.Diag(diag::warn_drv_argument_not_allowed_with)
<< "/vlen=256" << std::string("/arch:").append(Arch);
}
}

Arg *MostGeneralArg = Args.getLastArg(options::OPT__SLASH_vmg);
Arg *BestCaseArg = Args.getLastArg(options::OPT__SLASH_vmb);
if (MostGeneralArg && BestCaseArg)
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18 changes: 18 additions & 0 deletions clang/test/Driver/cl-x86-flags.c
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Expand Up @@ -133,6 +133,24 @@
// tune: "-target-cpu" "sandybridge"
// tune-SAME: "-tune-cpu" "haswell"

// RUN: %clang_cl -m64 -arch:AVX512 -vlen=512 --target=x86_64-pc-windows -### -- 2>&1 %s | FileCheck -check-prefix=vlen512 %s
// vlen512: "-mprefer-vector-width=512"

// RUN: %clang_cl -m64 -arch:AVX512 -vlen=256 --target=x86_64-pc-windows -### -- 2>&1 %s | FileCheck -check-prefix=vlen256 %s
// vlen256: "-mprefer-vector-width=256"

// RUN: %clang_cl -m64 -arch:AVX512 -vlen=512 -vlen --target=x86_64-pc-windows -### -- 2>&1 %s | FileCheck -check-prefix=noprefer %s
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@zmodem zmodem Nov 7, 2025

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how about novlen instead of noprefer?

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@phoebewang phoebewang Nov 7, 2025

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Done.

// noprefer-NOT: -mprefer-vector-width

// RUN: %clang_cl -m64 -arch:AVX2 -vlen=512 --target=x86_64-pc-windows -### -- 2>&1 %s | FileCheck -check-prefix=avx2vlen512 %s
// avx2vlen512: invalid argument '/vlen=512' not allowed with '/arch:AVX2'

// RUN: %clang_cl -m64 -arch:AVX2 -vlen=256 --target=x86_64-pc-windows -### -- 2>&1 %s | FileCheck -check-prefix=avx2vlen256 %s
// avx2vlen256-NOT: invalid argument

// RUN: %clang_cl -m32 -arch:SSE2 -vlen=256 --target=i386-pc-windows -### -- 2>&1 %s | FileCheck -check-prefix=sse2vlen256 %s
// sse2vlen256: invalid argument '/vlen=256' not allowed with '/arch:SSE2'

void f(void) {
}

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