[LoopRotate] Propagate dbg.value intrinsics

Recommitting patch which was previously reverted in r297159. These
changes should address the casting issues.

The original patch enables dbg.value intrinsics to be attached to
newly inserted PHI nodes.

Differential Review: https://reviews.llvm.org/D30701

llvm-svn: 297269

1 files changed, 45 insertions, 3 deletions

diff --git a/llvm/lib/Transforms/Scalar/LoopRotation.cpp b/llvm/lib/Transforms/Scalar/LoopRotation.cpp
index 0d57ce1e827..e5689368de8 100644
--- a/llvm/lib/Transforms/Scalar/LoopRotation.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopRotation.cpp
@@ -79,7 +79,8 @@ private:
 /// to merge the two values.  Do this now.
 static void RewriteUsesOfClonedInstructions(BasicBlock *OrigHeader,
                                             BasicBlock *OrigPreheader,
-                                            ValueToValueMapTy &ValueMap) {
+                                            ValueToValueMapTy &ValueMap,
+                                SmallVectorImpl<PHINode*> *InsertedPHIs) {
   // Remove PHI node entries that are no longer live.
   BasicBlock::iterator I, E = OrigHeader->end();
   for (I = OrigHeader->begin(); PHINode *PN = dyn_cast<PHINode>(I); ++I)
@@ -87,7 +88,7 @@ static void RewriteUsesOfClonedInstructions(BasicBlock *OrigHeader,
 
   // Now fix up users of the instructions in OrigHeader, inserting PHI nodes
   // as necessary.
-  SSAUpdater SSA;
+  SSAUpdater SSA(InsertedPHIs);
   for (I = OrigHeader->begin(); I != E; ++I) {
     Value *OrigHeaderVal = &*I;
 
@@ -174,6 +175,38 @@ static void RewriteUsesOfClonedInstructions(BasicBlock *OrigHeader,
   }
 }
 
+/// Propagate dbg.value intrinsics through the newly inserted Phis.
+static void insertDebugValues(BasicBlock *OrigHeader,
+                              SmallVectorImpl<PHINode*> &InsertedPHIs) {
+  ValueToValueMapTy DbgValueMap;
+
+  // Map existing PHI nodes to their dbg.values.
+  for (auto &I : *OrigHeader) {
+    if (auto DbgII = dyn_cast<DbgInfoIntrinsic>(&I)) {
+      if (auto *Loc = dyn_cast_or_null<PHINode>(DbgII->getVariableLocation()))
+        DbgValueMap.insert({Loc, DbgII});
+    }
+  }
+
+  // Then iterate through the new PHIs and look to see if they use one of the
+  // previously mapped PHIs. If so, insert a new dbg.value intrinsic that will
+  // propagate the info through the new PHI.
+  LLVMContext &C = OrigHeader->getContext();
+  for (auto PHI : InsertedPHIs) {
+    for (auto VI : PHI->operand_values()) {
+      auto V = DbgValueMap.find(VI);
+      if (V != DbgValueMap.end()) {
+        auto *DbgII = cast<DbgInfoIntrinsic>(V->second);
+        Instruction *NewDbgII = DbgII->clone();
+        auto PhiMAV = MetadataAsValue::get(C, ValueAsMetadata::get(PHI));
+        NewDbgII->setOperand(0, PhiMAV);
+        BasicBlock *Parent = PHI->getParent();
+        NewDbgII->insertBefore(Parent->getFirstNonPHIOrDbgOrLifetime());
+      }
+    }
+  }
+}
+
 /// Rotate loop LP. Return true if the loop is rotated.
 ///
 /// \param SimplifiedLatch is true if the latch was just folded into the final
@@ -347,9 +380,18 @@ bool LoopRotate::rotateLoop(Loop *L, bool SimplifiedLatch) {
   // remove the corresponding incoming values from the PHI nodes in OrigHeader.
   LoopEntryBranch->eraseFromParent();
 
+
+  SmallVector<PHINode*, 2> InsertedPHIs;
   // If there were any uses of instructions in the duplicated block outside the
   // loop, update them, inserting PHI nodes as required
-  RewriteUsesOfClonedInstructions(OrigHeader, OrigPreheader, ValueMap);
+  RewriteUsesOfClonedInstructions(OrigHeader, OrigPreheader, ValueMap,
+                                  &InsertedPHIs);
+
+  // Attach dbg.value intrinsics to the new phis if that phi uses a value that
+  // previously had debug metadata attached. This keeps the debug info
+  // up-to-date in the loop body.
+  if (!InsertedPHIs.empty())
+    insertDebugValues(OrigHeader, InsertedPHIs);
 
   // NewHeader is now the header of the loop.
   L->moveToHeader(NewHeader);