2 files changed, 64 insertions, 22 deletions

diff --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
index eaccaa1c4ac..94edf8ccab8 100644
--- a/llvm/lib/Transforms/Utils/Local.cpp
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -485,15 +485,19 @@ void llvm::RecursivelyDeleteTriviallyDeadInstructions(
     I.eraseFromParent();
   }
 }
+void llvm::setDbgVariableUndef(DbgVariableIntrinsic *DVI) {
+  Value *DbgValue = DVI->getVariableLocation(false);
+  Value *Undef = UndefValue::get(DbgValue ? DbgValue->getType()
+                                          : Type::getInt1Ty(DVI->getContext()));
+  DVI->setOperand(
+      0, MetadataAsValue::get(DVI->getContext(), ValueAsMetadata::get(Undef)));
+}
 
 bool llvm::replaceDbgUsesWithUndef(Instruction *I) {
   SmallVector<DbgVariableIntrinsic *, 1> DbgUsers;
   findDbgUsers(DbgUsers, I);
-  for (auto *DII : DbgUsers) {
-    Value *Undef = UndefValue::get(I->getType());
-    DII->setOperand(0, MetadataAsValue::get(DII->getContext(),
-                                            ValueAsMetadata::get(Undef)));
-  }
+  for (auto *DII : DbgUsers)
+    setDbgVariableUndef(DII);
   return !DbgUsers.empty();
 }
 
@@ -1040,6 +1044,19 @@ bool llvm::TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB,
       assert(PN->use_empty() && "There shouldn't be any uses here!");
       PN->eraseFromParent();
     }
+    // If Succ has multiple predecessors, each debug intrinsic in BB may or may
+    // not be valid when we reach Succ, so the debug variable should be set
+    // undef since its value is unknown.
+    Instruction *DbgInsertPoint = Succ->getFirstNonPHI();
+    while (DbgInfoIntrinsic *DI = dyn_cast<DbgInfoIntrinsic>(&BB->front())) {
+      if (auto DVI = cast<DbgVariableIntrinsic>(DI)) {
+        if (!isa<DbgDeclareInst>(DVI))
+          setDbgVariableUndef(DVI);
+        DVI->moveBefore(DbgInsertPoint);
+      } else {
+        break;
+      }
+    }
   }
 
   // If the unconditional branch we replaced contains llvm.loop metadata, we
diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 79d4857c2c8..0e74a26987c 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -13,6 +13,7 @@
 #include "llvm/ADT/APInt.h"
 #include "llvm/ADT/ArrayRef.h"
 #include "llvm/ADT/DenseMap.h"
+#include "llvm/ADT/MapVector.h"
 #include "llvm/ADT/Optional.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/ADT/SetOperations.h"
@@ -38,6 +39,7 @@
 #include "llvm/IR/ConstantRange.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/DataLayout.h"
+#include "llvm/IR/DebugInfoMetadata.h"
 #include "llvm/IR/DerivedTypes.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/GlobalValue.h"
@@ -1250,14 +1252,38 @@ static bool HoistThenElseCodeToIf(BranchInst *BI,
 
   Instruction *I1 = &*BB1_Itr++, *I2 = &*BB2_Itr++;
   // Skip debug info if it is not identical.
-  DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
-  DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
-  if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
-    while (isa<DbgInfoIntrinsic>(I1))
-      I1 = &*BB1_Itr++;
-    while (isa<DbgInfoIntrinsic>(I2))
-      I2 = &*BB2_Itr++;
-  }
+
+  // If the terminator instruction is hoisted, and any variable locations have
+  // non-identical debug intrinsics, then those variable locations must be set
+  // as undef.
+  // FIXME: If each block contains identical debug variable intrinsics in a
+  // different order, they will be considered non-identical and be dropped.
+  MapVector<DebugVariable, DbgVariableIntrinsic *> UndefDVIs;
+
+  auto SkipDbgInfo = [&UndefDVIs](Instruction *&I,
+                                  BasicBlock::iterator &BB_Itr) {
+    while (isa<DbgInfoIntrinsic>(I)) {
+      if (DbgVariableIntrinsic *DVI = dyn_cast<DbgVariableIntrinsic>(I))
+        UndefDVIs.insert(
+            {DebugVariable(DVI->getVariable(), DVI->getExpression(),
+                           DVI->getDebugLoc()->getInlinedAt()),
+             DVI});
+      I = &*BB_Itr++;
+    }
+  };
+
+  auto SkipNonIdenticalDbgInfo =
+      [&BB1_Itr, &BB2_Itr, &SkipDbgInfo](Instruction *&I1, Instruction *&I2) {
+        DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
+        DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
+        if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
+          SkipDbgInfo(I1, BB1_Itr);
+          SkipDbgInfo(I2, BB2_Itr);
+        }
+      };
+
+  SkipNonIdenticalDbgInfo(I1, I2);
+
   // FIXME: Can we define a safety predicate for CallBr?
   if (isa<PHINode>(I1) || !I1->isIdenticalToWhenDefined(I2) ||
       (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2)) ||
@@ -1330,15 +1356,7 @@ static bool HoistThenElseCodeToIf(BranchInst *BI,
 
     I1 = &*BB1_Itr++;
     I2 = &*BB2_Itr++;
-    // Skip debug info if it is not identical.
-    DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
-    DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
-    if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
-      while (isa<DbgInfoIntrinsic>(I1))
-        I1 = &*BB1_Itr++;
-      while (isa<DbgInfoIntrinsic>(I2))
-        I2 = &*BB2_Itr++;
-    }
+    SkipNonIdenticalDbgInfo(I1, I2);
   } while (I1->isIdenticalToWhenDefined(I2));
 
   return true;
@@ -1374,6 +1392,13 @@ HoistTerminator:
   }
 
   // Okay, it is safe to hoist the terminator.
+  for (auto DIVariableInst : UndefDVIs) {
+    DbgVariableIntrinsic *DVI = DIVariableInst.second;
+    DVI->moveBefore(BI);
+    if (Value *V = DVI->getVariableLocation())
+      setDbgVariableUndef(DVI);
+  }
+
   Instruction *NT = I1->clone();
   BIParent->getInstList().insert(BI->getIterator(), NT);
   if (!NT->getType()->isVoidTy()) {