[CodeGen][x86_64] Enable 'force_align_arg_pointer' attribute at x86_64

This attribute is useful in OS development when we jump from 32 to 64 bit
code and expect that 64bit function forces correct stack alignment.

Related discussion: http://lists.llvm.org/pipermail/cfe-dev/2017-June/054358.html

Patch By: anatol.pomozov (anatol.pomozov@gmail.com)

Differential Revision:https://reviews.llvm.org/D36272

llvm-svn: 312173

1 files changed, 18 insertions, 0 deletions

diff --git a/clang/lib/CodeGen/TargetInfo.cpp b/clang/lib/CodeGen/TargetInfo.cpp
index 77b9b4caab5..10fa2ea322c 100644
--- a/clang/lib/CodeGen/TargetInfo.cpp
+++ b/clang/lib/CodeGen/TargetInfo.cpp
@@ -2297,6 +2297,15 @@ public:
     if (!IsForDefinition)
       return;
     if (const FunctionDecl *FD = dyn_cast_or_null<FunctionDecl>(D)) {
+      if (FD->hasAttr<X86ForceAlignArgPointerAttr>()) {
+        // Get the LLVM function.
+        auto *Fn = cast<llvm::Function>(GV);
+
+        // Now add the 'alignstack' attribute with a value of 16.
+        llvm::AttrBuilder B;
+        B.addStackAlignmentAttr(16);
+        Fn->addAttributes(llvm::AttributeList::FunctionIndex, B);
+      }
       if (FD->hasAttr<AnyX86InterruptAttr>()) {
         llvm::Function *Fn = cast<llvm::Function>(GV);
         Fn->setCallingConv(llvm::CallingConv::X86_INTR);
@@ -2425,6 +2434,15 @@ void WinX86_64TargetCodeGenInfo::setTargetAttributes(
   if (!IsForDefinition)
     return;
   if (const FunctionDecl *FD = dyn_cast_or_null<FunctionDecl>(D)) {
+    if (FD->hasAttr<X86ForceAlignArgPointerAttr>()) {
+      // Get the LLVM function.
+      auto *Fn = cast<llvm::Function>(GV);
+
+      // Now add the 'alignstack' attribute with a value of 16.
+      llvm::AttrBuilder B;
+      B.addStackAlignmentAttr(16);
+      Fn->addAttributes(llvm::AttributeList::FunctionIndex, B);
+    }
     if (FD->hasAttr<AnyX86InterruptAttr>()) {
       llvm::Function *Fn = cast<llvm::Function>(GV);
       Fn->setCallingConv(llvm::CallingConv::X86_INTR);