[NFC][RemoveDIs] Insert instruction using iterators in Transforms/

As part of the RemoveDIs project we need LLVM to insert instructions using
iterators wherever possible, so that the iterators can carry a bit of
debug-info. This commit implements some of that by updating the contents of
llvm/lib/Transforms/Utils to always use iterator-versions of instruction
constructors.

There are two general flavours of update:
 * Almost all call-sites just call getIterator on an instruction
 * Several make use of an existing iterator (scenarios where the code is
   actually significant for debug-info)
The underlying logic is that any call to getFirstInsertionPt or similar
APIs that identify the start of a block need to have that iterator passed
directly to the insertion function, without being converted to a bare
Instruction pointer along the way.

Noteworthy changes:
 * FindInsertedValue now takes an optional iterator rather than an
   instruction pointer, as we need to always insert with iterators,
 * I've added a few iterator-taking versions of some value-tracking and
   DomTree methods -- they just unwrap the iterator. These are purely
   convenience methods to avoid extra syntax in some passes.
 * A few calls to getNextNode become std::next instead (to keep in the
   theme of using iterators for positions),
 * SeparateConstOffsetFromGEP has it's insertion-position field changed.
   Noteworthy because it's not a purely localised spelling change.

All this should be NFC.

1 files changed, 7 insertions, 6 deletions

diff --git a/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp b/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
index 7eb0ba1..3d14608 100644
--- a/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
+++ b/llvm/lib/Transforms/Scalar/SimpleLoopUnswitch.cpp
@@ -2347,8 +2347,7 @@ static void unswitchNontrivialInvariants(
       BI->setSuccessor(1 - ClonedSucc, LoopPH);
       Value *Cond = skipTrivialSelect(BI->getCondition());
       if (InsertFreeze)
-        Cond = new FreezeInst(
-            Cond, Cond->getName() + ".fr", BI);
+        Cond = new FreezeInst(Cond, Cond->getName() + ".fr", BI->getIterator());
       BI->setCondition(Cond);
       DTUpdates.push_back({DominatorTree::Insert, SplitBB, ClonedPH});
     } else {
@@ -2365,8 +2364,9 @@ static void unswitchNontrivialInvariants(
           Case.setSuccessor(ClonedPHs.find(Case.getCaseSuccessor())->second);
 
       if (InsertFreeze)
-        SI->setCondition(new FreezeInst(
-            SI->getCondition(), SI->getCondition()->getName() + ".fr", SI));
+        SI->setCondition(new FreezeInst(SI->getCondition(),
+                                        SI->getCondition()->getName() + ".fr",
+                                        SI->getIterator()));
 
       // We need to use the set to populate domtree updates as even when there
       // are multiple cases pointing at the same successor we only want to
@@ -2704,7 +2704,8 @@ static BranchInst *turnSelectIntoBranch(SelectInst *SI, DominatorTree &DT,
   if (MSSAU)
     MSSAU->moveAllAfterSpliceBlocks(HeadBB, TailBB, SI);
 
-  PHINode *Phi = PHINode::Create(SI->getType(), 2, "unswitched.select", SI);
+  PHINode *Phi =
+      PHINode::Create(SI->getType(), 2, "unswitched.select", SI->getIterator());
   Phi->addIncoming(SI->getTrueValue(), ThenBB);
   Phi->addIncoming(SI->getFalseValue(), HeadBB);
   SI->replaceAllUsesWith(Phi);
@@ -3092,7 +3093,7 @@ injectPendingInvariantConditions(NonTrivialUnswitchCandidate Candidate, Loop &L,
   // unswitching will break. Better optimize it away later.
   auto *InjectedCond =
       ICmpInst::Create(Instruction::ICmp, Pred, LHS, RHS, "injected.cond",
-                       Preheader->getTerminator());
+                       Preheader->getTerminator()->getIterator());
 
   BasicBlock *CheckBlock = BasicBlock::Create(Ctx, BB->getName() + ".check",
                                               BB->getParent(), InLoopSucc);