From 2d21b25393a461fbf8ab824889a6c56e1dd0b1cb Mon Sep 17 00:00:00 2001
From: Rafael Espindola <rafael.espindola@gmail.com>
Date: Tue, 3 Jun 2014 02:41:57 +0000
Subject: Allow alias to point to an arbitrary ConstantExpr.

This  patch changes GlobalAlias to point to an arbitrary ConstantExpr and it is
up to MC (or the system assembler) to decide if that expression is valid or not.

This reduces our ability to diagnose invalid uses and how early we can spot
them, but it also lets us do things like

@test5 = alias inttoptr(i32 sub (i32 ptrtoint (i32* @test2 to i32),
                                 i32 ptrtoint (i32* @bar to i32)) to i32*)

An important implication of this patch is that the notion of aliased global
doesn't exist any more. The alias has to encode the information needed to
access it in its metadata (linkage, visibility, type, etc).

Another consequence to notice is that getSection has to return a "const char *".
It could return a NullTerminatedStringRef if there was such a thing, but when
that was proposed the decision was to just uses "const char*" for that.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@210062 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/IR/Verifier.cpp | 63 ++++++++++++++++++++++++++++++++++-------------------
 1 file changed, 41 insertions(+), 22 deletions(-)

(limited to 'lib/IR/Verifier.cpp')

diff --git a/lib/IR/Verifier.cpp b/lib/IR/Verifier.cpp
index bcc38c1ad5..1719cb2759 100644
--- a/lib/IR/Verifier.cpp
+++ b/lib/IR/Verifier.cpp
@@ -241,6 +241,9 @@ private:
   void visitGlobalValue(const GlobalValue &GV);
   void visitGlobalVariable(const GlobalVariable &GV);
   void visitGlobalAlias(const GlobalAlias &GA);
+  void visitAliaseeSubExpr(const GlobalAlias &A, const Constant &C);
+  void visitAliaseeSubExpr(SmallPtrSet<const GlobalAlias *, 4> &Visited,
+                           const GlobalAlias &A, const Constant &C);
   void visitNamedMDNode(const NamedMDNode &NMD);
   void visitMDNode(MDNode &MD, Function *F);
   void visitModuleIdents(const Module &M);
@@ -474,36 +477,52 @@ void Verifier::visitGlobalVariable(const GlobalVariable &GV) {
   visitGlobalValue(GV);
 }
 
+void Verifier::visitAliaseeSubExpr(const GlobalAlias &GA, const Constant &C) {
+  SmallPtrSet<const GlobalAlias*, 4> Visited;
+  Visited.insert(&GA);
+  visitAliaseeSubExpr(Visited, GA, C);
+}
+
+void Verifier::visitAliaseeSubExpr(SmallPtrSet<const GlobalAlias *, 4> &Visited,
+                                   const GlobalAlias &GA, const Constant &C) {
+  if (const auto *GV = dyn_cast<GlobalValue>(&C)) {
+    Assert1(!GV->isDeclaration(), "Alias must point to a definition", &GA);
+
+    if (const auto *GA2 = dyn_cast<GlobalAlias>(GV)) {
+      Assert1(Visited.insert(GA2), "Aliases cannot form a cycle", &GA);
+
+      Assert1(!GA2->mayBeOverridden(), "Alias cannot point to a weak alias",
+              &GA);
+    }
+  }
+
+  if (const auto *CE = dyn_cast<ConstantExpr>(&C))
+    VerifyConstantExprBitcastType(CE);
+
+  for (const Use &U : C.operands()) {
+    Value *V = &*U;
+    if (const auto *GA2 = dyn_cast<GlobalAlias>(V))
+      visitAliaseeSubExpr(Visited, GA, *GA2->getAliasee());
+    else if (const auto *C2 = dyn_cast<Constant>(V))
+      visitAliaseeSubExpr(Visited, GA, *C2);
+  }
+}
+
 void Verifier::visitGlobalAlias(const GlobalAlias &GA) {
   Assert1(!GA.getName().empty(),
           "Alias name cannot be empty!", &GA);
   Assert1(GlobalAlias::isValidLinkage(GA.getLinkage()),
           "Alias should have external or external weak linkage!", &GA);
-  Assert1(GA.getAliasee(),
-          "Aliasee cannot be NULL!", &GA);
-  Assert1(!GA.hasUnnamedAddr(), "Alias cannot have unnamed_addr!", &GA);
-
   const Constant *Aliasee = GA.getAliasee();
-  const GlobalValue *GV = dyn_cast<GlobalValue>(Aliasee);
-
-  if (!GV) {
-    const ConstantExpr *CE = dyn_cast<ConstantExpr>(Aliasee);
-    if (CE && (CE->getOpcode() == Instruction::BitCast ||
-               CE->getOpcode() == Instruction::AddrSpaceCast ||
-               CE->getOpcode() == Instruction::GetElementPtr))
-      GV = dyn_cast<GlobalValue>(CE->getOperand(0));
+  Assert1(Aliasee, "Aliasee cannot be NULL!", &GA);
+  Assert1(GA.getType() == Aliasee->getType(),
+          "Alias and aliasee types should match!", &GA);
+  Assert1(!GA.hasUnnamedAddr(), "Alias cannot have unnamed_addr!", &GA);
 
-    Assert1(GV, "Aliasee should be either GlobalValue, bitcast or "
-                "addrspacecast of GlobalValue",
-            &GA);
+  Assert1(isa<GlobalValue>(Aliasee) || isa<ConstantExpr>(Aliasee),
+          "Aliasee should be either GlobalValue or ConstantExpr", &GA);
 
-    VerifyConstantExprBitcastType(CE);
-  }
-  Assert1(!GV->isDeclaration(), "Alias must point to a definition", &GA);
-  if (const GlobalAlias *GAAliasee = dyn_cast<GlobalAlias>(GV)) {
-    Assert1(!GAAliasee->mayBeOverridden(), "Alias cannot point to a weak alias",
-            &GA);
-  }
+  visitAliaseeSubExpr(GA, *Aliasee);
 
   visitGlobalValue(GA);
 }
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