[SCEVExpander] Remember phi nodes inserted by LCSSA construction

SCEVExpander keeps track of all instructions it inserted. However,
it currently misses some phi nodes created during LCSSA construction.
Fix this by collecting these into another argument.

This also removes the IRBuilder argument, which was added for
essentially the same purpose, but only handles the root LCSSA nodes,
not those inserted by SSAUpdater.

This was reported as a regression on D149344, but the reduced test
case also reproduces without it.

Differential Revision: https://reviews.llvm.org/D150681

1 files changed, 12 insertions, 13 deletions

diff --git a/llvm/lib/Transforms/Utils/LCSSA.cpp b/llvm/lib/Transforms/Utils/LCSSA.cpp
index a0a3186..a6895cc 100644
--- a/llvm/lib/Transforms/Utils/LCSSA.cpp
+++ b/llvm/lib/Transforms/Utils/LCSSA.cpp
@@ -40,7 +40,6 @@
 #include "llvm/Analysis/ScalarEvolutionAliasAnalysis.h"
 #include "llvm/IR/DebugInfo.h"
 #include "llvm/IR/Dominators.h"
-#include "llvm/IR/IRBuilder.h"
 #include "llvm/IR/Instructions.h"
 #include "llvm/IR/IntrinsicInst.h"
 #include "llvm/IR/PredIteratorCache.h"
@@ -77,15 +76,13 @@ static bool isExitBlock(BasicBlock *BB,
 /// rewrite the uses.
 bool llvm::formLCSSAForInstructions(SmallVectorImpl<Instruction *> &Worklist,
                                     const DominatorTree &DT, const LoopInfo &LI,
-                                    IRBuilderBase &Builder,
-                                    SmallVectorImpl<PHINode *> *PHIsToRemove) {
+                                    SmallVectorImpl<PHINode *> *PHIsToRemove,
+                                    SmallVectorImpl<PHINode *> *InsertedPHIs) {
   SmallVector<Use *, 16> UsesToRewrite;
   SmallSetVector<PHINode *, 16> LocalPHIsToRemove;
   PredIteratorCache PredCache;
   bool Changed = false;
 
-  IRBuilderBase::InsertPointGuard InsertPtGuard(Builder);
-
   // Cache the Loop ExitBlocks across this loop.  We expect to get a lot of
   // instructions within the same loops, computing the exit blocks is
   // expensive, and we're not mutating the loop structure.
@@ -146,8 +143,8 @@ bool llvm::formLCSSAForInstructions(SmallVectorImpl<Instruction *> &Worklist,
     SmallVector<PHINode *, 16> AddedPHIs;
     SmallVector<PHINode *, 8> PostProcessPHIs;
 
-    SmallVector<PHINode *, 4> InsertedPHIs;
-    SSAUpdater SSAUpdate(&InsertedPHIs);
+    SmallVector<PHINode *, 4> LocalInsertedPHIs;
+    SSAUpdater SSAUpdate(&LocalInsertedPHIs);
     SSAUpdate.Initialize(I->getType(), I->getName());
 
     // Insert the LCSSA phi's into all of the exit blocks dominated by the
@@ -159,9 +156,10 @@ bool llvm::formLCSSAForInstructions(SmallVectorImpl<Instruction *> &Worklist,
       // If we already inserted something for this BB, don't reprocess it.
       if (SSAUpdate.HasValueForBlock(ExitBB))
         continue;
-      Builder.SetInsertPoint(&ExitBB->front());
-      PHINode *PN = Builder.CreatePHI(I->getType(), PredCache.size(ExitBB),
-                                      I->getName() + ".lcssa");
+      PHINode *PN = PHINode::Create(I->getType(), PredCache.size(ExitBB),
+                                    I->getName() + ".lcssa", &ExitBB->front());
+      if (InsertedPHIs)
+        InsertedPHIs->push_back(PN);
       // Get the debug location from the original instruction.
       PN->setDebugLoc(I->getDebugLoc());
 
@@ -251,10 +249,12 @@ bool llvm::formLCSSAForInstructions(SmallVectorImpl<Instruction *> &Worklist,
 
     // SSAUpdater might have inserted phi-nodes inside other loops. We'll need
     // to post-process them to keep LCSSA form.
-    for (PHINode *InsertedPN : InsertedPHIs) {
+    for (PHINode *InsertedPN : LocalInsertedPHIs) {
       if (auto *OtherLoop = LI.getLoopFor(InsertedPN->getParent()))
         if (!L->contains(OtherLoop))
           PostProcessPHIs.push_back(InsertedPN);
+      if (InsertedPHIs)
+        InsertedPHIs->push_back(InsertedPN);
     }
 
     // Post process PHI instructions that were inserted into another disjoint
@@ -386,8 +386,7 @@ bool llvm::formLCSSA(Loop &L, const DominatorTree &DT, const LoopInfo *LI) {
     }
   }
 
-  IRBuilder<> Builder(L.getHeader()->getContext());
-  Changed = formLCSSAForInstructions(Worklist, DT, *LI, Builder);
+  Changed = formLCSSAForInstructions(Worklist, DT, *LI);
 
   assert(L.isLCSSAForm(DT));