5 files changed, 51 insertions, 0 deletions
diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index a21527abba1..17d9db3399f 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -1238,6 +1238,10 @@ void CodeGenModule::SetLLVMFunctionAttributesForDefinition(const Decl *D,
   if (alignment)
     F->setAlignment(alignment);
 
+  if (!D->hasAttr<AlignedAttr>())
+    if (LangOpts.FunctionAlignment)
+      F->setAlignment(1 << LangOpts.FunctionAlignment);
+
   // Some C++ ABIs require 2-byte alignment for member functions, in order to
   // reserve a bit for differentiating between virtual and non-virtual member
   // functions. If the current target's C++ ABI requires this and this is a
diff --git a/clang/lib/Driver/ToolChains/Clang.cpp b/clang/lib/Driver/ToolChains/Clang.cpp
index 15e7cf2847c..e96b5b7590f 100644
--- a/clang/lib/Driver/ToolChains/Clang.cpp
+++ b/clang/lib/Driver/ToolChains/Clang.cpp
@@ -3323,6 +3323,13 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
 
   CheckCodeGenerationOptions(D, Args);
 
+  unsigned FunctionAlignment = ParseFunctionAlignment(getToolChain(), Args);
+  assert(FunctionAlignment <= 31 && "function alignment will be truncated!");
+  if (FunctionAlignment) {
+    CmdArgs.push_back("-function-alignment");
+    CmdArgs.push_back(Args.MakeArgString(std::to_string(FunctionAlignment)));
+  }
+
   llvm::Reloc::Model RelocationModel;
   unsigned PICLevel;
   bool IsPIE;
diff --git a/clang/lib/Driver/ToolChains/CommonArgs.cpp b/clang/lib/Driver/ToolChains/CommonArgs.cpp
index 869cf4c8f2e..1527238c663 100644
--- a/clang/lib/Driver/ToolChains/CommonArgs.cpp
+++ b/clang/lib/Driver/ToolChains/CommonArgs.cpp
@@ -1033,6 +1033,40 @@ tools::ParsePICArgs(const ToolChain &ToolChain, const ArgList &Args) {
   return std::make_tuple(RelocM, 0U, false);
 }
 
+// `-falign-functions` indicates that the functions should be aligned to a
+// 16-byte boundary.
+//
+// `-falign-functions=1` is the same as `-fno-align-functions`.
+//
+// The scalar `n` in `-falign-functions=n` must be an integral value between
+// [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.
+//
+// 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) {
+  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->getOption().matches(options::OPT_falign_functions))
+    return 0;
+
+  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;
+}
+
 void tools::AddAssemblerKPIC(const ToolChain &ToolChain, const ArgList &Args,
                              ArgStringList &CmdArgs) {
   llvm::Reloc::Model RelocationModel;
diff --git a/clang/lib/Driver/ToolChains/CommonArgs.h b/clang/lib/Driver/ToolChains/CommonArgs.h
index 14db1ea7302..10a03d4a178 100644
--- a/clang/lib/Driver/ToolChains/CommonArgs.h
+++ b/clang/lib/Driver/ToolChains/CommonArgs.h
@@ -66,6 +66,9 @@ void AddGoldPlugin(const ToolChain &ToolChain, const llvm::opt::ArgList &Args,
 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);
+
 void AddAssemblerKPIC(const ToolChain &ToolChain,
                       const llvm::opt::ArgList &Args,
                       llvm::opt::ArgStringList &CmdArgs);
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index 9146d2a36df..67e15b41add 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -2968,6 +2968,9 @@ bool CompilerInvocation::CreateFromArgs(CompilerInvocation &Res,
       LangOpts.ObjCExceptions = 1;
   }
 
+  LangOpts.FunctionAlignment =
+      getLastArgIntValue(Args, OPT_function_alignment, 0, Diags);
+
   if (LangOpts.CUDA) {
     // During CUDA device-side compilation, the aux triple is the
     // triple used for host compilation.