IR: Split Metadata from Value

Split `Metadata` away from the `Value` class hierarchy, as part of
PR21532.  Assembly and bitcode changes are in the wings, but this is the
bulk of the change for the IR C++ API.

I have a follow-up patch prepared for `clang`.  If this breaks other
sub-projects, I apologize in advance :(.  Help me compile it on Darwin
I'll try to fix it.  FWIW, the errors should be easy to fix, so it may
be simpler to just fix it yourself.

This breaks the build for all metadata-related code that's out-of-tree.
Rest assured the transition is mechanical and the compiler should catch
almost all of the problems.

Here's a quick guide for updating your code:

  - `Metadata` is the root of a class hierarchy with three main classes:
    `MDNode`, `MDString`, and `ValueAsMetadata`.  It is distinct from
    the `Value` class hierarchy.  It is typeless -- i.e., instances do
    *not* have a `Type`.

  - `MDNode`'s operands are all `Metadata *` (instead of `Value *`).

  - `TrackingVH<MDNode>` and `WeakVH` referring to metadata can be
    replaced with `TrackingMDNodeRef` and `TrackingMDRef`, respectively.

    If you're referring solely to resolved `MDNode`s -- post graph
    construction -- just use `MDNode*`.

  - `MDNode` (and the rest of `Metadata`) have only limited support for
    `replaceAllUsesWith()`.

    As long as an `MDNode` is pointing at a forward declaration -- the
    result of `MDNode::getTemporary()` -- it maintains a side map of its
    uses and can RAUW itself.  Once the forward declarations are fully
    resolved RAUW support is dropped on the ground.  This means that
    uniquing collisions on changing operands cause nodes to become
    "distinct".  (This already happened fairly commonly, whenever an
    operand went to null.)

    If you're constructing complex (non self-reference) `MDNode` cycles,
    you need to call `MDNode::resolveCycles()` on each node (or on a
    top-level node that somehow references all of the nodes).  Also,
    don't do that.  Metadata cycles (and the RAUW machinery needed to
    construct them) are expensive.

  - An `MDNode` can only refer to a `Constant` through a bridge called
    `ConstantAsMetadata` (one of the subclasses of `ValueAsMetadata`).

    As a side effect, accessing an operand of an `MDNode` that is known
    to be, e.g., `ConstantInt`, takes three steps: first, cast from
    `Metadata` to `ConstantAsMetadata`; second, extract the `Constant`;
    third, cast down to `ConstantInt`.

    The eventual goal is to introduce `MDInt`/`MDFloat`/etc. and have
    metadata schema owners transition away from using `Constant`s when
    the type isn't important (and they don't care about referring to
    `GlobalValue`s).

    In the meantime, I've added transitional API to the `mdconst`
    namespace that matches semantics with the old code, in order to
    avoid adding the error-prone three-step equivalent to every call
    site.  If your old code was:

        MDNode *N = foo();
        bar(isa             <ConstantInt>(N->getOperand(0)));
        baz(cast            <ConstantInt>(N->getOperand(1)));
        bak(cast_or_null    <ConstantInt>(N->getOperand(2)));
        bat(dyn_cast        <ConstantInt>(N->getOperand(3)));
        bay(dyn_cast_or_null<ConstantInt>(N->getOperand(4)));

    you can trivially match its semantics with:

        MDNode *N = foo();
        bar(mdconst::hasa               <ConstantInt>(N->getOperand(0)));
        baz(mdconst::extract            <ConstantInt>(N->getOperand(1)));
        bak(mdconst::extract_or_null    <ConstantInt>(N->getOperand(2)));
        bat(mdconst::dyn_extract        <ConstantInt>(N->getOperand(3)));
        bay(mdconst::dyn_extract_or_null<ConstantInt>(N->getOperand(4)));

    and when you transition your metadata schema to `MDInt`:

        MDNode *N = foo();
        bar(isa             <MDInt>(N->getOperand(0)));
        baz(cast            <MDInt>(N->getOperand(1)));
        bak(cast_or_null    <MDInt>(N->getOperand(2)));
        bat(dyn_cast        <MDInt>(N->getOperand(3)));
        bay(dyn_cast_or_null<MDInt>(N->getOperand(4)));

  - A `CallInst` -- specifically, intrinsic instructions -- can refer to
    metadata through a bridge called `MetadataAsValue`.  This is a
    subclass of `Value` where `getType()->isMetadataTy()`.

    `MetadataAsValue` is the *only* class that can legally refer to a
    `LocalAsMetadata`, which is a bridged form of non-`Constant` values
    like `Argument` and `Instruction`.  It can also refer to any other
    `Metadata` subclass.

(I'll break all your testcases in a follow-up commit, when I propagate
this change to assembly.)

llvm-svn: 223802

4 files changed, 27 insertions, 17 deletions

diff --git a/llvm/lib/Analysis/BranchProbabilityInfo.cpp b/llvm/lib/Analysis/BranchProbabilityInfo.cpp
index bbd87505952..2b39d47e5fa 100644
--- a/llvm/lib/Analysis/BranchProbabilityInfo.cpp
+++ b/llvm/lib/Analysis/BranchProbabilityInfo.cpp
@@ -196,7 +196,8 @@ bool BranchProbabilityInfo::calcMetadataWeights(BasicBlock *BB) {
   SmallVector<uint32_t, 2> Weights;
   Weights.reserve(TI->getNumSuccessors());
   for (unsigned i = 1, e = WeightsNode->getNumOperands(); i != e; ++i) {
-    ConstantInt *Weight = dyn_cast<ConstantInt>(WeightsNode->getOperand(i));
+    ConstantInt *Weight =
+        mdconst::dyn_extract<ConstantInt>(WeightsNode->getOperand(i));
     if (!Weight)
       return false;
     Weights.push_back(
diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 792542eab25..177bd23030a 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -3750,8 +3750,10 @@ static Optional<ConstantRange> GetRangeFromMetadata(Value *V) {
       assert(NumRanges >= 1);
 
       for (unsigned i = 0; i < NumRanges; ++i) {
-        ConstantInt *Lower = cast<ConstantInt>(MD->getOperand(2*i + 0));
-        ConstantInt *Upper = cast<ConstantInt>(MD->getOperand(2*i + 1));
+        ConstantInt *Lower =
+            mdconst::extract<ConstantInt>(MD->getOperand(2 * i + 0));
+        ConstantInt *Upper =
+            mdconst::extract<ConstantInt>(MD->getOperand(2 * i + 1));
         ConstantRange Range(Lower->getValue(), Upper->getValue());
         TotalRange = TotalRange.unionWith(Range);
       }
diff --git a/llvm/lib/Analysis/TypeBasedAliasAnalysis.cpp b/llvm/lib/Analysis/TypeBasedAliasAnalysis.cpp
index f347eb5f191..085ce920139 100644
--- a/llvm/lib/Analysis/TypeBasedAliasAnalysis.cpp
+++ b/llvm/lib/Analysis/TypeBasedAliasAnalysis.cpp
@@ -167,7 +167,7 @@ namespace {
     bool TypeIsImmutable() const {
       if (Node->getNumOperands() < 3)
         return false;
-      ConstantInt *CI = dyn_cast<ConstantInt>(Node->getOperand(2));
+      ConstantInt *CI = mdconst::dyn_extract<ConstantInt>(Node->getOperand(2));
       if (!CI)
         return false;
       return CI->getValue()[0];
@@ -194,7 +194,7 @@ namespace {
       return dyn_cast_or_null<MDNode>(Node->getOperand(1));
     }
     uint64_t getOffset() const {
-      return cast<ConstantInt>(Node->getOperand(2))->getZExtValue();
+      return mdconst::extract<ConstantInt>(Node->getOperand(2))->getZExtValue();
     }
     /// TypeIsImmutable - Test if this TBAAStructTagNode represents a type for
     /// objects which are not modified (by any means) in the context where this
@@ -202,7 +202,7 @@ namespace {
     bool TypeIsImmutable() const {
       if (Node->getNumOperands() < 4)
         return false;
-      ConstantInt *CI = dyn_cast<ConstantInt>(Node->getOperand(3));
+      ConstantInt *CI = mdconst::dyn_extract<ConstantInt>(Node->getOperand(3));
       if (!CI)
         return false;
       return CI->getValue()[0];
@@ -233,8 +233,10 @@ namespace {
       // Fast path for a scalar type node and a struct type node with a single
       // field.
       if (Node->getNumOperands() <= 3) {
-        uint64_t Cur = Node->getNumOperands() == 2 ? 0 :
-                       cast<ConstantInt>(Node->getOperand(2))->getZExtValue();
+        uint64_t Cur = Node->getNumOperands() == 2
+                           ? 0
+                           : mdconst::extract<ConstantInt>(Node->getOperand(2))
+                                 ->getZExtValue();
         Offset -= Cur;
         MDNode *P = dyn_cast_or_null<MDNode>(Node->getOperand(1));
         if (!P)
@@ -246,8 +248,8 @@ namespace {
       // the current offset is bigger than the given offset.
       unsigned TheIdx = 0;
       for (unsigned Idx = 1; Idx < Node->getNumOperands(); Idx += 2) {
-        uint64_t Cur = cast<ConstantInt>(Node->getOperand(Idx + 1))->
-                         getZExtValue();
+        uint64_t Cur = mdconst::extract<ConstantInt>(Node->getOperand(Idx + 1))
+                           ->getZExtValue();
         if (Cur > Offset) {
           assert(Idx >= 3 &&
                  "TBAAStructTypeNode::getParent should have an offset match!");
@@ -258,8 +260,8 @@ namespace {
       // Move along the last field.
       if (TheIdx == 0)
         TheIdx = Node->getNumOperands() - 2;
-      uint64_t Cur = cast<ConstantInt>(Node->getOperand(TheIdx + 1))->
-                       getZExtValue();
+      uint64_t Cur = mdconst::extract<ConstantInt>(Node->getOperand(TheIdx + 1))
+                         ->getZExtValue();
       Offset -= Cur;
       MDNode *P = dyn_cast_or_null<MDNode>(Node->getOperand(TheIdx));
       if (!P)
@@ -608,7 +610,8 @@ MDNode *MDNode::getMostGenericTBAA(MDNode *A, MDNode *B) {
     return nullptr;
   // We need to convert from a type node to a tag node.
   Type *Int64 = IntegerType::get(A->getContext(), 64);
-  Value *Ops[3] = { Ret, Ret, ConstantInt::get(Int64, 0) };
+  Metadata *Ops[3] = {Ret, Ret,
+                      ConstantAsMetadata::get(ConstantInt::get(Int64, 0))};
   return MDNode::get(A->getContext(), Ops);
 }
 
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index ced5151582f..fa428fa108d 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -312,8 +312,10 @@ void llvm::computeKnownBitsFromRangeMetadata(const MDNode &Ranges,
   // Use the high end of the ranges to find leading zeros.
   unsigned MinLeadingZeros = BitWidth;
   for (unsigned i = 0; i < NumRanges; ++i) {
-    ConstantInt *Lower = cast<ConstantInt>(Ranges.getOperand(2*i + 0));
-    ConstantInt *Upper = cast<ConstantInt>(Ranges.getOperand(2*i + 1));
+    ConstantInt *Lower =
+        mdconst::extract<ConstantInt>(Ranges.getOperand(2 * i + 0));
+    ConstantInt *Upper =
+        mdconst::extract<ConstantInt>(Ranges.getOperand(2 * i + 1));
     ConstantRange Range(Lower->getValue(), Upper->getValue());
     if (Range.isWrappedSet())
       MinLeadingZeros = 0; // -1 has no zeros
@@ -1504,8 +1506,10 @@ static bool rangeMetadataExcludesValue(MDNode* Ranges,
   const unsigned NumRanges = Ranges->getNumOperands() / 2;
   assert(NumRanges >= 1);
   for (unsigned i = 0; i < NumRanges; ++i) {
-    ConstantInt *Lower = cast<ConstantInt>(Ranges->getOperand(2*i + 0));
-    ConstantInt *Upper = cast<ConstantInt>(Ranges->getOperand(2*i + 1));
+    ConstantInt *Lower =
+        mdconst::extract<ConstantInt>(Ranges->getOperand(2 * i + 0));
+    ConstantInt *Upper =
+        mdconst::extract<ConstantInt>(Ranges->getOperand(2 * i + 1));
     ConstantRange Range(Lower->getValue(), Upper->getValue());
     if (Range.contains(Value))
       return false;