MC: prevent early DCE of empty sections

[oota-llvm.git] / lib / IR / Globals.cpp

diff --git a/lib/IR/Globals.cpp b/lib/IR/Globals.cpp
index dd2a4e435ec2a6f378e7aaefbf346372eb69111b..160ddc9e81a74972a2d695465722b65d59cb2866 100644 (file)
--- a/lib/IR/Globals.cpp
+++ b/lib/IR/Globals.cpp
@@ -20,6 +20,7 @@
 #include "llvm/IR/GlobalVariable.h"
 #include "llvm/IR/LeakDetector.h"
 #include "llvm/IR/Module.h"
+#include "llvm/IR/Operator.h"
 #include "llvm/Support/ErrorHandling.h"
 using namespace llvm;
 
@@ -58,10 +59,22 @@ void GlobalValue::copyAttributesFrom(const GlobalValue *Src) {
   setDLLStorageClass(Src->getDLLStorageClass());
 }
 
-unsigned GlobalValue::getAlignment() const {
-  if (auto *GA = dyn_cast<GlobalAlias>(this))
-    return GA->getAliasee()->getAlignment();
+const GlobalObject *getBaseObject(const Constant &C) {
+  // FIXME: We should probably return a base + offset pair for non-zero GEPs.
+  return dyn_cast<GlobalObject>(C.stripPointerCasts());
+}
 
+unsigned GlobalValue::getAlignment() const {
+  if (auto *GA = dyn_cast<GlobalAlias>(this)) {
+    // In general we cannot compute this at the IR level, but we try.
+    if (const GlobalObject *GO = getBaseObject(*GA->getAliasee()))
+      return GO->getAlignment();
+
+    // FIXME: we should also be able to handle:
+    // Alias = Global + Offset
+    // Alias = Absolute
+    return 0;
+  }
   return cast<GlobalObject>(this)->getAlignment();
 }
 
@@ -80,9 +93,13 @@ void GlobalObject::copyAttributesFrom(const GlobalValue *Src) {
   setSection(GV->getSection());
 }
 
-const std::string &GlobalValue::getSection() const {
-  if (auto *GA = dyn_cast<GlobalAlias>(this))
-    return GA->getAliasee()->getSection();
+const char *GlobalValue::getSection() const {
+  if (auto *GA = dyn_cast<GlobalAlias>(this)) {
+    // In general we cannot compute this at the IR level, but we try.
+    if (const GlobalObject *GO = getBaseObject(*GA->getAliasee()))
+      return GO->getSection();
+    return "";
+  }
   return cast<GlobalObject>(this)->getSection();
 }
 
@@ -113,8 +130,9 @@ GlobalVariable::GlobalVariable(Type *Ty, bool constant, LinkageTypes Link,
     : GlobalObject(PointerType::get(Ty, AddressSpace), Value::GlobalVariableVal,
                    OperandTraits<GlobalVariable>::op_begin(this),
                    InitVal != nullptr, Link, Name),
-      isConstantGlobal(constant), threadLocalMode(TLMode),
+      isConstantGlobal(constant),
       isExternallyInitializedConstant(isExternallyInitialized) {
+  setThreadLocalMode(TLMode);
   if (InitVal) {
     assert(InitVal->getType() == Ty &&
            "Initializer should be the same type as the GlobalVariable!");
@@ -132,8 +150,9 @@ GlobalVariable::GlobalVariable(Module &M, Type *Ty, bool constant,
     : GlobalObject(PointerType::get(Ty, AddressSpace), Value::GlobalVariableVal,
                    OperandTraits<GlobalVariable>::op_begin(this),
                    InitVal != nullptr, Link, Name),
-      isConstantGlobal(constant), threadLocalMode(TLMode),
+      isConstantGlobal(constant),
       isExternallyInitializedConstant(isExternallyInitialized) {
+  setThreadLocalMode(TLMode);
   if (InitVal) {
     assert(InitVal->getType() == Ty &&
            "Initializer should be the same type as the GlobalVariable!");
@@ -213,9 +232,9 @@ void GlobalVariable::copyAttributesFrom(const GlobalValue *Src) {
 // GlobalAlias Implementation
 //===----------------------------------------------------------------------===//
 
-GlobalAlias::GlobalAlias(Type *Ty, LinkageTypes Link, const Twine &Name,
-                         GlobalObject *Aliasee, Module *ParentModule,
-                         unsigned AddressSpace)
+GlobalAlias::GlobalAlias(Type *Ty, unsigned AddressSpace, LinkageTypes Link,
+                         const Twine &Name, Constant *Aliasee,
+                         Module *ParentModule)
     : GlobalValue(PointerType::get(Ty, AddressSpace), Value::GlobalAliasVal,
                   &Op<0>(), 1, Link, Name) {
   LeakDetector::addGarbageObject(this);
@@ -225,6 +244,35 @@ GlobalAlias::GlobalAlias(Type *Ty, LinkageTypes Link, const Twine &Name,
     ParentModule->getAliasList().push_back(this);
 }
 
+GlobalAlias *GlobalAlias::create(Type *Ty, unsigned AddressSpace,
+                                 LinkageTypes Link, const Twine &Name,
+                                 Constant *Aliasee, Module *ParentModule) {
+  return new GlobalAlias(Ty, AddressSpace, Link, Name, Aliasee, ParentModule);
+}
+
+GlobalAlias *GlobalAlias::create(Type *Ty, unsigned AddressSpace,
+                                 LinkageTypes Linkage, const Twine &Name,
+                                 Module *Parent) {
+  return create(Ty, AddressSpace, Linkage, Name, nullptr, Parent);
+}
+
+GlobalAlias *GlobalAlias::create(Type *Ty, unsigned AddressSpace,
+                                 LinkageTypes Linkage, const Twine &Name,
+                                 GlobalValue *Aliasee) {
+  return create(Ty, AddressSpace, Linkage, Name, Aliasee, Aliasee->getParent());
+}
+
+GlobalAlias *GlobalAlias::create(LinkageTypes Link, const Twine &Name,
+                                 GlobalValue *Aliasee) {
+  PointerType *PTy = Aliasee->getType();
+  return create(PTy->getElementType(), PTy->getAddressSpace(), Link, Name,
+                Aliasee);
+}
+
+GlobalAlias *GlobalAlias::create(const Twine &Name, GlobalValue *Aliasee) {
+  return create(Aliasee->getLinkage(), Name, Aliasee);
+}
+
 void GlobalAlias::setParent(Module *parent) {
   if (getParent())
     LeakDetector::addGarbageObject(this);
@@ -241,4 +289,8 @@ void GlobalAlias::eraseFromParent() {
   getParent()->getAliasList().erase(this);
 }
 
-void GlobalAlias::setAliasee(GlobalObject *Aliasee) { setOperand(0, Aliasee); }
+void GlobalAlias::setAliasee(Constant *Aliasee) {
+  assert((!Aliasee || Aliasee->getType() == getType()) &&
+         "Alias and aliasee types should match!");
+  setOperand(0, Aliasee);
+}