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

Ref:
https://learn.microsoft.com/en-us/cpp/build/reference/vlen?view=msvc-170

Author: phoebewang

clang/include/clang/Basic/DiagnosticDriverKinds.td

@@ -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<

clang/include/clang/Driver/Options.td

@@ -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>">,

clang/lib/Driver/ToolChains/Clang.cpp

@@ -8266,6 +8266,30 @@ 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::Triple::ArchType AT = getToolChain().getArch();
+    StringRef Default = AT == llvm::Triple::x86 ? "IA32" : "SSE2";
+    StringRef Arch = Args.getLastArgValue(options::OPT__SLASH_arch, Default);
+
+    if (A->getOption().matches(options::OPT__SLASH_vlen_EQ_512)) {
+      if (Arch == "AVX512F" || Arch == "AVX512")
+        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 (Arch == "AVX512F" || Arch == "AVX512")
+        CmdArgs.push_back("-mprefer-vector-width=256");
+      else if (Arch != "AVX" && Arch != "AVX2")
+        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)

clang/test/Driver/cl-x86-flags.c

@@ -133,6 +133,28 @@
 // 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=novlen %s
+// novlen-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
+// RUN: %clang_cl -m64 -vlen=256 --target=x86_64-pc-windows -### -- 2>&1 %s | FileCheck -check-prefix=sse2vlen256 %s
+// sse2vlen256: invalid argument '/vlen=256' not allowed with '/arch:SSE2'
+
+// RUN: %clang_cl -m32 -vlen=256 --target=i386-pc-windows -### -- 2>&1 %s | FileCheck -check-prefix=ia32vlen256 %s
+// ia32vlen256: invalid argument '/vlen=256' not allowed with '/arch:IA32'
+
 void f(void) {
 }