Clarify that llvm.used can contain aliases.

Also add a check for llvm.used in the verifier and simplify clients now that
they can assume they have a ConstantArray.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@180019 91177308-0d34-0410-b5e6-96231b3b80d8

docs/LangRef.rst

@@ -2868,9 +2868,9 @@ All globals of this sort should have a section specified as
 The '``llvm.used``' Global Variable
 -----------------------------------
 
-The ``@llvm.used`` global is an array with i8\* element type which has
-:ref:`appending linkage <linkage_appending>`. This array contains a list of
-pointers to global variables and functions which may optionally have a
+The ``@llvm.used`` global is an array which has
+ :ref:`appending linkage <linkage_appending>`. This array contains a list of
+pointers to global variables, functions and aliases which may optionally have a
 pointer cast formed of bitcast or getelementptr. For example, a legal
 use of it is:
 
@@ -2884,13 +2884,13 @@ use of it is:
        i8* bitcast (i32* @Y to i8*)
     ], section "llvm.metadata"
 
-If a global variable appears in the ``@llvm.used`` list, then the
-compiler, assembler, and linker are required to treat the symbol as if
-there is a reference to the global that it cannot see. For example, if a
-variable has internal linkage and no references other than that from the
-``@llvm.used`` list, it cannot be deleted. This is commonly used to
-represent references from inline asms and other things the compiler
-cannot "see", and corresponds to "``attribute((used))``" in GNU C.
+If a symbol appears in the ``@llvm.used`` list, then the compiler, assembler,
+and linker are required to treat the symbol as if there is a reference to the
+symbol that it cannot see. For example, if a variable has internal linkage and
+no references other than that from the ``@llvm.used`` list, it cannot be
+deleted. This is commonly used to represent references from inline asms and
+other things the compiler cannot "see", and corresponds to
+"``attribute((used))``" in GNU C.
 
 On some targets, the code generator must emit a directive to the
 assembler or object file to prevent the assembler and linker from

include/llvm/CodeGen/AsmPrinter.h

@@ -25,6 +25,7 @@ namespace llvm {
   class BlockAddress;
   class GCStrategy;
   class Constant;
+  class ConstantArray;
   class GCMetadataPrinter;
   class GlobalValue;
   class GlobalVariable;
@@ -480,7 +481,7 @@ namespace llvm {
     void EmitJumpTableEntry(const MachineJumpTableInfo *MJTI,
                             const MachineBasicBlock *MBB,
                             unsigned uid) const;
-    void EmitLLVMUsedList(const Constant *List);
+    void EmitLLVMUsedList(const ConstantArray *InitList);
     void EmitXXStructorList(const Constant *List, bool isCtor);
     GCMetadataPrinter *GetOrCreateGCPrinter(GCStrategy *C);
   };

lib/CodeGen/AsmPrinter/AsmPrinter.cpp

@@ -1213,7 +1213,7 @@ void AsmPrinter::EmitJumpTableEntry(const MachineJumpTableInfo *MJTI,
 bool AsmPrinter::EmitSpecialLLVMGlobal(const GlobalVariable *GV) {
   if (GV->getName() == "llvm.used") {
     if (MAI->hasNoDeadStrip())    // No need to emit this at all.
-      EmitLLVMUsedList(GV->getInitializer());
+      EmitLLVMUsedList(cast<ConstantArray>(GV->getInitializer()));
     return true;
   }
 
@@ -1256,11 +1256,8 @@ bool AsmPrinter::EmitSpecialLLVMGlobal(const GlobalVariable *GV) {
 /// EmitLLVMUsedList - For targets that define a MAI::UsedDirective, mark each
 /// global in the specified llvm.used list for which emitUsedDirectiveFor
 /// is true, as being used with this directive.
-void AsmPrinter::EmitLLVMUsedList(const Constant *List) {
+void AsmPrinter::EmitLLVMUsedList(const ConstantArray *InitList) {
   // Should be an array of 'i8*'.
-  const ConstantArray *InitList = dyn_cast<ConstantArray>(List);
-  if (InitList == 0) return;
-
   for (unsigned i = 0, e = InitList->getNumOperands(); i != e; ++i) {
     const GlobalValue *GV =
       dyn_cast<GlobalValue>(InitList->getOperand(i)->stripPointerCasts());

lib/CodeGen/MachineModuleInfo.cpp

@@ -326,8 +326,7 @@ void MachineModuleInfo::AnalyzeModule(const Module &M) {
   if (!GV || !GV->hasInitializer()) return;
 
   // Should be an array of 'i8*'.
-  const ConstantArray *InitList = dyn_cast<ConstantArray>(GV->getInitializer());
-  if (InitList == 0) return;
+  const ConstantArray *InitList = cast<ConstantArray>(GV->getInitializer());
 
   for (unsigned i = 0, e = InitList->getNumOperands(); i != e; ++i)
     if (const Function *F =

lib/IR/Verifier.cpp

@@ -449,6 +449,29 @@ void Verifier::visitGlobalVariable(GlobalVariable &GV) {
     }
   }
 
+  if (GV.hasName() && (GV.getName() == "llvm.used")) {
+    Assert1(!GV.hasInitializer() || GV.hasAppendingLinkage(),
+            "invalid linkage for intrinsic global variable", &GV);
+    Type *GVType = GV.getType()->getElementType();
+    if (ArrayType *ATy = dyn_cast<ArrayType>(GVType)) {
+      PointerType *PTy = dyn_cast<PointerType>(ATy->getElementType());
+      Assert1(PTy, "wrong type for intrinsic global variable", &GV);
+      if (GV.hasInitializer()) {
+        Constant *Init = GV.getInitializer();
+        ConstantArray *InitArray = dyn_cast<ConstantArray>(Init);
+        Assert1(InitArray, "wrong initalizer for intrinsic global variable",
+                Init);
+        for (unsigned i = 0, e = InitArray->getNumOperands(); i != e; ++i) {
+          Value *V = Init->getOperand(i)->stripPointerCasts();
+          // stripPointerCasts strips aliases, so we only need to check for
+          // variables and functions.
+          Assert1(isa<GlobalVariable>(V) || isa<Function>(V),
+                  "invalid llvm.used member", V);
+        }
+      }
+    }
+  }
+
   visitGlobalValue(GV);
 }
 

lib/Transforms/IPO/ConstantMerge.cpp

@@ -66,9 +66,8 @@ ModulePass *llvm::createConstantMergePass() { return new ConstantMerge(); }
 static void FindUsedValues(GlobalVariable *LLVMUsed,
                            SmallPtrSet<const GlobalValue*, 8> &UsedValues) {
   if (LLVMUsed == 0) return;
-  ConstantArray *Inits = dyn_cast<ConstantArray>(LLVMUsed->getInitializer());
-  if (Inits == 0) return;
-  
+  ConstantArray *Inits = cast<ConstantArray>(LLVMUsed->getInitializer());
+
   for (unsigned i = 0, e = Inits->getNumOperands(); i != e; ++i)
     if (GlobalValue *GV = 
         dyn_cast<GlobalValue>(Inits->getOperand(i)->stripPointerCasts()))

lib/Transforms/IPO/StripSymbols.cpp

@@ -195,10 +195,9 @@ static void findUsedValues(GlobalVariable *LLVMUsed,
                            SmallPtrSet<const GlobalValue*, 8> &UsedValues) {
   if (LLVMUsed == 0) return;
   UsedValues.insert(LLVMUsed);
-  
-  ConstantArray *Inits = dyn_cast<ConstantArray>(LLVMUsed->getInitializer());
-  if (Inits == 0) return;
-  
+
+  ConstantArray *Inits = cast<ConstantArray>(LLVMUsed->getInitializer());
+
   for (unsigned i = 0, e = Inits->getNumOperands(); i != e; ++i)
     if (GlobalValue *GV = 
           dyn_cast<GlobalValue>(Inits->getOperand(i)->stripPointerCasts()))

lib/Transforms/Scalar/GlobalMerge.cpp

@@ -200,9 +200,8 @@ void GlobalMerge::collectUsedGlobalVariables(Module &M) {
   if (!GV || !GV->hasInitializer()) return;
 
   // Should be an array of 'i8*'.
-  const ConstantArray *InitList = dyn_cast<ConstantArray>(GV->getInitializer());
-  if (InitList == 0) return;
- 
+  const ConstantArray *InitList = cast<ConstantArray>(GV->getInitializer());
+
   for (unsigned i = 0, e = InitList->getNumOperands(); i != e; ++i)
     if (const GlobalVariable *G =
         dyn_cast<GlobalVariable>(InitList->getOperand(i)->stripPointerCasts()))

test/Feature/aliases.ll

@@ -2,6 +2,8 @@
 ; RUN: llvm-as %t1.ll -o - | llvm-dis > %t2.ll
 ; RUN: diff %t1.ll %t2.ll
 
+@llvm.used = appending global [1 x i8*] [i8* bitcast (i32* @foo1 to i8*)], section "llvm.metadata"
+
 @bar = external global i32
 @foo1 = alias i32* @bar
 @foo2 = alias i32* @bar

test/Verifier/llvm.used-invalid-init.ll

@@ -0,0 +1,6 @@
+; RUN: not llvm-as < %s -o /dev/null 2>&1 | FileCheck %s
+
+@llvm.used = appending global [1 x i8*] zeroinitializer, section "llvm.metadata"
+
+; CHECK: wrong initalizer for intrinsic global variable
+; CHECK-NEXT: [1 x i8*] zeroinitializer

test/Verifier/llvm.used-invalid-init2.ll

@@ -0,0 +1,7 @@
+; RUN: not llvm-as < %s -o /dev/null 2>&1 | FileCheck %s
+
+@a = global i8 42
+@llvm.used = appending global [2 x i8*] [i8* @a, i8* null], section "llvm.metadata"
+
+; CHECK: invalid llvm.used member
+; CHECK-NEXT: i8* null

test/Verifier/llvm.used-invalid-type.ll

@@ -0,0 +1,6 @@
+; RUN: not llvm-as < %s -o /dev/null 2>&1 | FileCheck %s
+
+@llvm.used = appending global [1 x i32] [i32 0], section "llvm.metadata"
+
+; CHECK:       wrong type for intrinsic global variable
+; CHECK-NEXT: [1 x i32]* @llvm.used

test/Verifier/llvm.used-invalid-type2.ll

@@ -0,0 +1,5 @@
+; RUN: not llvm-as < %s -o /dev/null 2>&1 | FileCheck %s
+@llvm.used = appending global i32 0, section "llvm.metadata"
+
+; CHECK: Only global arrays can have appending linkage!
+; CHEKC-NEXT: i32* @llvm.used

test/Verifier/llvm.used-ptr-type.ll

@@ -0,0 +1,4 @@
+; RUN: llvm-as < %s -o /dev/null
+
+@a = global i32 42
+@llvm.used = appending global [1 x i32*] [i32* @a], section "llvm.metadata"