Add !callees metadata

This patch adds a new kind of metadata that indicates the possible callees of
indirect calls.

Differential Revision: https://reviews.llvm.org/D37354

llvm-svn: 315944

llvm/docs/LangRef.rst

@@ -4878,6 +4878,23 @@ Example (assuming 64-bit pointers):
     !0 = !{ i64 0, i64 256 }
     !1 = !{ i64 -1, i64 -1 }
 
+'``callees``' Metadata
+^^^^^^^^^^^^^^^^^^^^^^
+
+``callees`` metadata may be attached to indirect call sites. If ``callees``
+metadata is attached to a call site, and any callee is not among the set of
+functions provided by the metadata, the behavior is undefined. The intent of
+this metadata is to facilitate optimizations such as indirect-call promotion.
+For example, in the code below, the call instruction may only target the
+``add`` or ``sub`` functions:
+
+.. code-block:: llvm
+
+    %result = call i64 %binop(i64 %x, i64 %y), !callees !0
+
+    ...
+    !0 = !{i64 (i64, i64)* @add, i64 (i64, i64)* @sub}
+
 '``unpredictable``' Metadata
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 

llvm/include/llvm/IR/LLVMContext.h

@@ -100,6 +100,7 @@ public:
     MD_section_prefix = 20,           // "section_prefix"
     MD_absolute_symbol = 21,          // "absolute_symbol"
     MD_associated = 22,               // "associated"
+    MD_callees = 23,                  // "callees"
   };
 
   /// Known operand bundle tag IDs, which always have the same value.  All

llvm/include/llvm/IR/MDBuilder.h

@@ -84,6 +84,14 @@ public:
   /// \brief Return metadata describing the range [Lo, Hi).
   MDNode *createRange(Constant *Lo, Constant *Hi);
 
+  //===------------------------------------------------------------------===//
+  // Callees metadata.
+  //===------------------------------------------------------------------===//
+
+  /// \brief Return metadata indicating the possible callees of indirect
+  /// calls.
+  MDNode *createCallees(ArrayRef<Function *> Callees);
+
   //===------------------------------------------------------------------===//
   // AA metadata.
   //===------------------------------------------------------------------===//

llvm/lib/IR/LLVMContext.cpp

@@ -59,6 +59,7 @@ LLVMContext::LLVMContext() : pImpl(new LLVMContextImpl(*this)) {
     {MD_section_prefix, "section_prefix"},
     {MD_absolute_symbol, "absolute_symbol"},
     {MD_associated, "associated"},
+    {MD_callees, "callees"},
   };
 
   for (auto &MDKind : MDKinds) {

llvm/lib/IR/MDBuilder.cpp

@@ -14,6 +14,7 @@
 
 #include "llvm/IR/MDBuilder.h"
 #include "llvm/IR/Constants.h"
+#include "llvm/IR/Function.h"
 #include "llvm/IR/Metadata.h"
 using namespace llvm;
 
@@ -95,6 +96,13 @@ MDNode *MDBuilder::createRange(Constant *Lo, Constant *Hi) {
   return MDNode::get(Context, {createConstant(Lo), createConstant(Hi)});
 }
 
+MDNode *MDBuilder::createCallees(ArrayRef<Function *> Callees) {
+  SmallVector<Metadata *, 4> Ops;
+  for (Function *F : Callees)
+    Ops.push_back(createConstant(F));
+  return MDNode::get(Context, Ops);
+}
+
 MDNode *MDBuilder::createAnonymousAARoot(StringRef Name, MDNode *Extra) {
   // To ensure uniqueness the root node is self-referential.
   auto Dummy = MDNode::getTemporary(Context, None);

llvm/test/ThinLTO/X86/lazyload_metadata.ll

@@ -10,13 +10,13 @@
 ; RUN: llvm-lto -thinlto-action=import %t2.bc -thinlto-index=%t3.bc \
 ; RUN:          -o /dev/null -stats \
 ; RUN:  2>&1 | FileCheck %s -check-prefix=LAZY
-; LAZY: 51 bitcode-reader  - Number of Metadata records loaded
+; LAZY: 53 bitcode-reader  - Number of Metadata records loaded
 ; LAZY: 2 bitcode-reader  - Number of MDStrings loaded
 
 ; RUN: llvm-lto -thinlto-action=import %t2.bc -thinlto-index=%t3.bc \
 ; RUN:          -o /dev/null -disable-ondemand-mds-loading -stats \
 ; RUN:  2>&1 | FileCheck %s -check-prefix=NOTLAZY
-; NOTLAZY: 60 bitcode-reader  - Number of Metadata records loaded
+; NOTLAZY: 62 bitcode-reader  - Number of Metadata records loaded
 ; NOTLAZY: 7 bitcode-reader  - Number of MDStrings loaded