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

1 files changed, 1 insertions, 34 deletions

diff --git a/lib/Bitcode/Reader/BitcodeReader.cpp b/lib/Bitcode/Reader/BitcodeReader.cpp
index 3d4ae84dbd..322879b566 100644
--- a/lib/Bitcode/Reader/BitcodeReader.cpp
+++ b/lib/Bitcode/Reader/BitcodeReader.cpp
@@ -1094,28 +1094,6 @@ uint64_t BitcodeReader::decodeSignRotatedValue(uint64_t V) {
   return 1ULL << 63;
 }
 
-// FIXME: Delete this in LLVM 4.0 and just assert that the aliasee is a
-// GlobalObject.
-static GlobalObject &
-getGlobalObjectInExpr(const DenseMap<GlobalAlias *, Constant *> &Map,
-                      Constant &C) {
-  auto *GO = dyn_cast<GlobalObject>(&C);
-  if (GO)
-    return *GO;
-
-  auto *GA = dyn_cast<GlobalAlias>(&C);
-  if (GA)
-    return getGlobalObjectInExpr(Map, *Map.find(GA)->second);
-
-  auto &CE = cast<ConstantExpr>(C);
-  assert(CE.getOpcode() == Instruction::BitCast ||
-         CE.getOpcode() == Instruction::GetElementPtr ||
-         CE.getOpcode() == Instruction::AddrSpaceCast);
-  if (CE.getOpcode() == Instruction::GetElementPtr)
-    assert(cast<GEPOperator>(CE).hasAllZeroIndices());
-  return getGlobalObjectInExpr(Map, *CE.getOperand(0));
-}
-
 /// ResolveGlobalAndAliasInits - Resolve all of the initializers for global
 /// values and aliases that we can.
 error_code BitcodeReader::ResolveGlobalAndAliasInits() {
@@ -1141,30 +1119,19 @@ error_code BitcodeReader::ResolveGlobalAndAliasInits() {
     GlobalInitWorklist.pop_back();
   }
 
-  // FIXME: Delete this in LLVM 4.0
-  // Older versions of llvm could write an alias pointing to another. We cannot
-  // construct those aliases, so we first collect an alias to aliasee expression
-  // and then compute the actual aliasee.
-  DenseMap<GlobalAlias *, Constant *> AliasInit;
-
   while (!AliasInitWorklist.empty()) {
     unsigned ValID = AliasInitWorklist.back().second;
     if (ValID >= ValueList.size()) {
       AliasInits.push_back(AliasInitWorklist.back());
     } else {
       if (Constant *C = dyn_cast_or_null<Constant>(ValueList[ValID]))
-        AliasInit.insert(std::make_pair(AliasInitWorklist.back().first, C));
+        AliasInitWorklist.back().first->setAliasee(C);
       else
         return Error(ExpectedConstant);
     }
     AliasInitWorklist.pop_back();
   }
 
-  for (auto &Pair : AliasInit) {
-    auto &GO = getGlobalObjectInExpr(AliasInit, *Pair.second);
-    Pair.first->setAliasee(&GO);
-  }
-
   while (!FunctionPrefixWorklist.empty()) {
     unsigned ValID = FunctionPrefixWorklist.back().second;
     if (ValID >= ValueList.size()) {