Implement global merge optimization for global variables.

This commit implements two command line switches -global-merge-on-external
and -global-merge-aligned, and both of them are false by default, so this
optimization is disabled by default for all targets.

For ARM64, some back-end behaviors need to be tuned to get this optimization
further enabled.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208934 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 25 insertions, 0 deletions

diff --git a/lib/IR/Globals.cpp b/lib/IR/Globals.cpp
index 0ec54fe3c0..d64046a7bf 100644
--- a/lib/IR/Globals.cpp
+++ b/lib/IR/Globals.cpp
@@ -15,6 +15,7 @@
 #include "llvm/IR/GlobalValue.h"
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/IR/Constants.h"
+#include "llvm/IR/DataLayout.h"
 #include "llvm/IR/DerivedTypes.h"
 #include "llvm/IR/GlobalAlias.h"
 #include "llvm/IR/GlobalVariable.h"
@@ -282,3 +283,27 @@ GlobalObject *GlobalAlias::getAliasedGlobal() {
       return cast<GlobalObject>(GV);
   }
 }
+
+uint64_t GlobalAlias::calculateOffset(const DataLayout &DL) const {
+  uint64_t Offset = 0;
+  const Constant *C = this;
+  while (C) {
+    if (const GlobalAlias *GA = dyn_cast<GlobalAlias>(C)) {
+      C = GA->getAliasee();
+    } else if (const ConstantExpr *CE = dyn_cast<ConstantExpr>(C)) {
+      if (CE->getOpcode() == Instruction::GetElementPtr) {
+        std::vector<Value*> Args;
+        for (unsigned I = 1; I < CE->getNumOperands(); ++I)
+          Args.push_back(CE->getOperand(I));
+        Offset += DL.getIndexedOffset(CE->getOperand(0)->getType(), Args);
+      }
+      C = CE->getOperand(0);
+    } else if (isa<GlobalValue>(C)) {
+      return Offset;
+    } else {
+      assert(0 && "Unexpected type in alias chain!");
+      return 0;
+    }
+  }
+  return Offset;
+}