Begin adding docs and IR-level support for the inalloca attribute

The inalloca attribute is designed to support passing C++ objects by
value in the Microsoft C++ ABI.  It behaves the same as byval, except
that it always implies that the argument is in memory and that the bytes
are never copied.  This attribute allows the caller to take the address
of an outgoing argument's memory and execute arbitrary code to store
into it.

This patch adds basic IR support, docs, and verification.  It does not
attempt to implement any lowering or fix any possibly broken transforms.

When this patch lands, a complete description of this feature should
appear at http://llvm.org/docs/InAlloca.html .

Differential Revision: http://llvm-reviews.chandlerc.com/D2173

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@197645 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 16 insertions, 0 deletions

diff --git a/include/llvm/Support/CallSite.h b/include/llvm/Support/CallSite.h
index 2a1c5ca4d4..d2c47b53ed 100644
--- a/include/llvm/Support/CallSite.h
+++ b/include/llvm/Support/CallSite.h
@@ -257,6 +257,22 @@ public:
     return paramHasAttr(ArgNo + 1, Attribute::ByVal);
   }
 
+  /// @brief Determine whether this argument is passed in an alloca.
+  bool isInAllocaArgument(unsigned ArgNo) const {
+    return paramHasAttr(ArgNo + 1, Attribute::InAlloca);
+  }
+
+  /// @brief Determine whether this argument is passed by value or in an alloca.
+  bool isByValOrInAllocaArgument(unsigned ArgNo) const {
+    return paramHasAttr(ArgNo + 1, Attribute::ByVal) ||
+           paramHasAttr(ArgNo + 1, Attribute::InAlloca);
+  }
+
+  /// @brief Determine if there are any inalloca arguments.
+  bool hasInAllocaArgument() const {
+    return getAttributes().hasAttrSomewhere(Attribute::InAlloca);
+  }
+
   bool doesNotAccessMemory(unsigned ArgNo) const {
     return paramHasAttr(ArgNo + 1, Attribute::ReadNone);
   }