IR, X86: Understand !absolute_symbol metadata on global variables.

Summary:
Attaching !absolute_symbol to a global variable does two things:
1) Marks it as an absolute symbol reference.
2) Specifies the value range of that symbol's address.
Teach the X86 backend to allow absolute symbols to appear in place of
immediates by extending the relocImm and mov64imm32 matchers. Start using
relocImm in more places where it is legal.

As previously proposed on llvm-dev:
http://lists.llvm.org/pipermail/llvm-dev/2016-October/105800.html

Differential Revision: https://reviews.llvm.org/D25878

llvm-svn: 289087

1 files changed, 21 insertions, 0 deletions

diff --git a/llvm/lib/IR/Globals.cpp b/llvm/lib/IR/Globals.cpp
index f8ac37f9fc3..7cad629eaa7 100644
--- a/llvm/lib/IR/Globals.cpp
+++ b/llvm/lib/IR/Globals.cpp
@@ -15,6 +15,7 @@
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/ADT/Triple.h"
 #include "llvm/IR/Constants.h"
+#include "llvm/IR/ConstantRange.h"
 #include "llvm/IR/DerivedTypes.h"
 #include "llvm/IR/GlobalAlias.h"
 #include "llvm/IR/GlobalValue.h"
@@ -222,6 +223,26 @@ GlobalObject *GlobalValue::getBaseObject() {
   return nullptr;
 }
 
+bool GlobalValue::isAbsoluteSymbolRef() const {
+  auto *GO = dyn_cast<GlobalObject>(this);
+  if (!GO)
+    return false;
+
+  return GO->getMetadata(LLVMContext::MD_absolute_symbol);
+}
+
+Optional<ConstantRange> GlobalValue::getAbsoluteSymbolRange() const {
+  auto *GO = dyn_cast<GlobalObject>(this);
+  if (!GO)
+    return None;
+
+  MDNode *MD = GO->getMetadata(LLVMContext::MD_absolute_symbol);
+  if (!MD)
+    return None;
+
+  return getConstantRangeFromMetadata(*MD);
+}
+
 //===----------------------------------------------------------------------===//
 // GlobalVariable Implementation
 //===----------------------------------------------------------------------===//