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

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Phoebe Wang (phoebewang)

<details>
<summary>Changes</summary>

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

---
Full diff: https://github.com/llvm/llvm-project/pull/166375.diff


4 Files Affected:

- (modified) clang/include/clang/Basic/DiagnosticDriverKinds.td (+3) 
- (modified) clang/include/clang/Driver/Options.td (+4) 
- (modified) clang/lib/Driver/ToolChains/Clang.cpp (+31) 
- (modified) clang/test/Driver/cl-x86-flags.c (+21) 


``````````diff
diff --git a/clang/include/clang/Basic/DiagnosticDriverKinds.td b/clang/include/clang/Basic/DiagnosticDriverKinds.td
index 83980e3ac35b7..e657abb86d95f 100644
--- a/clang/include/clang/Basic/DiagnosticDriverKinds.td
+++ b/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<
diff --git a/clang/include/clang/Driver/Options.td b/clang/include/clang/Driver/Options.td
index 11e81e032d5fc..e271444184e44 100644
--- a/clang/include/clang/Driver/Options.td
+++ b/clang/include/clang/Driver/Options.td
@@ -9218,6 +9218,10 @@ def : CLFlag<"Qscatter-">, Alias<mno_scatter>,
 
 def _SLASH_arch : CLCompileJoined<"arch:">,
   HelpText<"Set architecture for code generation">;
+def _SLASH_vlen : CLCompileJoined<"vlen">,
+  HelpText<"Set vector length for autovectorization and other optimizations">;
+def _SLASH_vlen_default : CLFlag<"vlen">,
+  HelpText<"Set default vector length for autovectorization and other optimizations">;
 
 def _SLASH_M_Group : OptionGroup<"</M group>">, Group<cl_compile_Group>;
 def _SLASH_volatile_Group : OptionGroup<"</volatile group>">,
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index 30d3e5293a31b..add34c63d9c24 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -8266,6 +8266,37 @@ void Clang::AddClangCLArgs(const ArgList &Args, types::ID InputType,
                                                      << "/kernel";
  }
 
+  if (Args.hasArg(options::OPT__SLASH_vlen_default)) {
+    // Override /vlen= options.
+    for (const Arg *A : Args.filtered(options::OPT__SLASH_vlen))
+      A->claim();
+    // Nothing to do for AVX512F/AVX512.
+  } else if (const Arg *A = Args.getLastArg(options::OPT__SLASH_vlen)) {
+    StringRef VLen = A->getValue();
+    llvm::SmallSet<std::string, 4> Arch512 = {"AVX512F", "AVX512"};
+    llvm::SmallSet<std::string, 4> Arch256 = {"AVX", "AVX2"};
+
+    StringRef Arch = Args.getLastArgValue(options::OPT__SLASH_arch);
+    if (Arch != "") {
+      if (VLen == "=512") {
+        if (Arch512.contains(Arch.str()))
+          CmdArgs.push_back("-mprefer-vector-width=512");
+        else
+          D.Diag(diag::warn_drv_argument_not_allowed_with)
+              << "/vlen=512" << std::string("/arch:").append(Arch);
+      } else if (VLen == "=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);
+      } else {
+          D.Diag(diag::warn_drv_unknown_argument_clang_cl)
+              << std::string("/vlen").append(VLen);
+      }
+    }
+  }
+
   Arg *MostGeneralArg = Args.getLastArg(options::OPT__SLASH_vmg);
   Arg *BestCaseArg = Args.getLastArg(options::OPT__SLASH_vmb);
   if (MostGeneralArg && BestCaseArg)
diff --git a/clang/test/Driver/cl-x86-flags.c b/clang/test/Driver/cl-x86-flags.c
index 89526744c0a49..56cfcb420f4ad 100644
--- a/clang/test/Driver/cl-x86-flags.c
+++ b/clang/test/Driver/cl-x86-flags.c
@@ -133,6 +133,27 @@
 // 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
+// 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'
+
+// RUN: %clang_cl -m64 -arch:AVX -vlen256 --target=x86_64-pc-windows -### -- 2>&1 %s | FileCheck -check-prefix=avxvlen256 %s
+// avxvlen256: unknown argument ignored in clang-cl: '/vlen256'
+
 void f(void) {
 }
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/166375