[IR] Begin removal of TerminatorInst by removing successor manipulation.

The core get and set routines move to the `Instruction` class. These
routines are only valid to call on instructions which are terminators.

The iterator and *generic* range based access move to `CFG.h` where all
the other generic successor and predecessor access lives. While moving
the iterator here, simplify it using the iterator utilities LLVM
provides and updates coding style as much as reasonable. The APIs remain
pointer-heavy when they could better use references, and retain the odd
behavior of `operator*` and `operator->` that is common in LLVM
iterators. Adjusting this API, if desired, should be a follow-up step.

Non-generic range iteration is added for the two instructions where
there is an especially easy mechanism and where there was code
attempting to use the range accessor from a specific subclass:
`indirectbr` and `br`. In both cases, the successors are contiguous
operands and can be easily iterated via the operand list.

This is the first major patch in removing the `TerminatorInst` type from
the IR's instruction type hierarchy. This change was discussed in an RFC
here and was pretty clearly positive:
http://lists.llvm.org/pipermail/llvm-dev/2018-May/123407.html

There will be a series of much more mechanical changes following this
one to complete this move.

Differential Revision: https://reviews.llvm.org/D47467

llvm-svn: 340698

5 files changed, 5 insertions, 6 deletions

diff --git a/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp b/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
index d1b9cb6c954..279aef6fcbb 100644
--- a/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
+++ b/llvm/lib/Transforms/Utils/BasicBlockUtils.cpp
@@ -59,7 +59,7 @@ void llvm::DeleteDeadBlock(BasicBlock *BB, DomTreeUpdater *DTU) {
   // of their predecessors is going away.
   if (DTU)
     Updates.reserve(BBTerm->getNumSuccessors());
-  for (BasicBlock *Succ : BBTerm->successors()) {
+  for (BasicBlock *Succ : successors(BBTerm)) {
     Succ->removePredecessor(BB);
     if (DTU)
       Updates.push_back({DominatorTree::Delete, BB, Succ});
diff --git a/llvm/lib/Transforms/Utils/CloneFunction.cpp b/llvm/lib/Transforms/Utils/CloneFunction.cpp
index 5dbe6e9ac76..4a51424a4da 100644
--- a/llvm/lib/Transforms/Utils/CloneFunction.cpp
+++ b/llvm/lib/Transforms/Utils/CloneFunction.cpp
@@ -415,7 +415,7 @@ void PruningFunctionCloner::CloneBlock(const BasicBlock *BB,
 
     // Recursively clone any reachable successor blocks.
     const TerminatorInst *TI = BB->getTerminator();
-    for (const BasicBlock *Succ : TI->successors())
+    for (const BasicBlock *Succ : successors(TI))
       ToClone.push_back(Succ);
   }
 
diff --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
index 5ac66742c7c..e3be924de87 100644
--- a/llvm/lib/Transforms/Utils/Local.cpp
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -235,7 +235,7 @@ bool llvm::ConstantFoldTerminator(BasicBlock *BB, bool DeleteDeadConditions,
         Updates.reserve(SI->getNumSuccessors() - 1);
 
       // Remove entries from PHI nodes which we no longer branch to...
-      for (BasicBlock *Succ : SI->successors()) {
+      for (BasicBlock *Succ : successors(SI)) {
         // Found case matching a constant operand?
         if (Succ == TheOnlyDest) {
           TheOnlyDest = nullptr; // Don't modify the first branch to TheOnlyDest
diff --git a/llvm/lib/Transforms/Utils/LoopRotationUtils.cpp b/llvm/lib/Transforms/Utils/LoopRotationUtils.cpp
index 514c594ddfa..e7319637319 100644
--- a/llvm/lib/Transforms/Utils/LoopRotationUtils.cpp
+++ b/llvm/lib/Transforms/Utils/LoopRotationUtils.cpp
@@ -375,8 +375,7 @@ bool LoopRotate::rotateLoop(Loop *L, bool SimplifiedLatch) {
   // Along with all the other instructions, we just cloned OrigHeader's
   // terminator into OrigPreHeader. Fix up the PHI nodes in each of OrigHeader's
   // successors by duplicating their incoming values for OrigHeader.
-  TerminatorInst *TI = OrigHeader->getTerminator();
-  for (BasicBlock *SuccBB : TI->successors())
+  for (BasicBlock *SuccBB : successors(OrigHeader))
     for (BasicBlock::iterator BI = SuccBB->begin();
          PHINode *PN = dyn_cast<PHINode>(BI); ++BI)
       PN->addIncoming(PN->getIncomingValueForBlock(OrigHeader), OrigPreheader);
diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 28ed77adb18..06f7844e8bd 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -3414,7 +3414,7 @@ static bool SimplifyTerminatorOnSelect(TerminatorInst *OldTerm, Value *Cond,
   BasicBlock *KeepEdge2 = TrueBB != FalseBB ? FalseBB : nullptr;
 
   // Then remove the rest.
-  for (BasicBlock *Succ : OldTerm->successors()) {
+  for (BasicBlock *Succ : successors(OldTerm)) {
     // Make sure only to keep exactly one copy of each edge.
     if (Succ == KeepEdge1)
       KeepEdge1 = nullptr;