diff --git a/clang/test/Misc/loop-opt-setup.c b/clang/test/Misc/loop-opt-setup.c
--- a/clang/test/Misc/loop-opt-setup.c
+++ b/clang/test/Misc/loop-opt-setup.c
@@ -23,8 +23,8 @@
         --num_active;
 }
 
-// Check br i1 to make sure the loop is gone, there will still be a label branch for the infinite loop.
+// Check br i1 to make sure the loop is gone, there will be no loop here.
 // CHECK-LABEL: Helper
-// CHECK: br label
+// CHECK: entry:
 // CHECK-NOT: br i1
-// CHECK: br label
+// CHECK-NEXT: ret void
diff --git a/llvm/include/llvm/Analysis/LoopInfo.h b/llvm/include/llvm/Analysis/LoopInfo.h
--- a/llvm/include/llvm/Analysis/LoopInfo.h
+++ b/llvm/include/llvm/Analysis/LoopInfo.h
@@ -302,6 +302,8 @@
   /// Otherwise return null.
   BlockT *getUniqueExitBlock() const;
 
+  unsigned getNumExitBlocks() const;
+
   /// Edge type.
   typedef std::pair<BlockT *, BlockT *> Edge;
 
diff --git a/llvm/include/llvm/Analysis/LoopInfoImpl.h b/llvm/include/llvm/Analysis/LoopInfoImpl.h
--- a/llvm/include/llvm/Analysis/LoopInfoImpl.h
+++ b/llvm/include/llvm/Analysis/LoopInfoImpl.h
@@ -135,6 +135,13 @@
   return nullptr;
 }
 
+template <class BlockT, class LoopT>
+unsigned LoopBase<BlockT, LoopT>::getNumExitBlocks() const {
+  SmallVector<BlockT *, 8> UniqueExitBlocks;
+  getUniqueExitBlocks(UniqueExitBlocks);
+  return UniqueExitBlocks.size();
+}
+
 /// getExitEdges - Return all pairs of (_inside_block_,_outside_block_).
 template <class BlockT, class LoopT>
 void LoopBase<BlockT, LoopT>::getExitEdges(
diff --git a/llvm/include/llvm/Transforms/Utils/LoopUtils.h b/llvm/include/llvm/Transforms/Utils/LoopUtils.h
--- a/llvm/include/llvm/Transforms/Utils/LoopUtils.h
+++ b/llvm/include/llvm/Transforms/Utils/LoopUtils.h
@@ -229,6 +229,9 @@
 /// Look for the loop attribute that disables the LICM transformation heuristics.
 bool hasDisableLICMTransformsHint(const Loop *L);
 
+/// Look for the loop attribute that requires progress within the loop.
+bool hasMustProgress(const Loop *L);
+
 /// The mode sets how eager a transformation should be applied.
 enum TransformationMode {
   /// The pass can use heuristics to determine whether a transformation should
diff --git a/llvm/lib/Transforms/Scalar/LoopDeletion.cpp b/llvm/lib/Transforms/Scalar/LoopDeletion.cpp
--- a/llvm/lib/Transforms/Scalar/LoopDeletion.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopDeletion.cpp
@@ -53,26 +53,28 @@
   // of the loop.
   bool AllEntriesInvariant = true;
   bool AllOutgoingValuesSame = true;
-  for (PHINode &P : ExitBlock->phis()) {
-    Value *incoming = P.getIncomingValueForBlock(ExitingBlocks[0]);
-
-    // Make sure all exiting blocks produce the same incoming value for the exit
-    // block.  If there are different incoming values for different exiting
-    // blocks, then it is impossible to statically determine which value should
-    // be used.
-    AllOutgoingValuesSame =
-        all_of(makeArrayRef(ExitingBlocks).slice(1), [&](BasicBlock *BB) {
-          return incoming == P.getIncomingValueForBlock(BB);
-        });
-
-    if (!AllOutgoingValuesSame)
-      break;
-
-    if (Instruction *I = dyn_cast<Instruction>(incoming))
-      if (!L->makeLoopInvariant(I, Changed, Preheader->getTerminator())) {
-        AllEntriesInvariant = false;
+  if (L->getNumExitBlocks() != 0) {
+    for (PHINode &P : ExitBlock->phis()) {
+      Value *incoming = P.getIncomingValueForBlock(ExitingBlocks[0]);
+
+      // Make sure all exiting blocks produce the same incoming value for the
+      // exit block.  If there are different incoming values for different
+      // exiting blocks, then it is impossible to statically determine which
+      // value should be used.
+      AllOutgoingValuesSame =
+          all_of(makeArrayRef(ExitingBlocks).slice(1), [&](BasicBlock *BB) {
+            return incoming == P.getIncomingValueForBlock(BB);
+          });
+
+      if (!AllOutgoingValuesSame)
         break;
-      }
+
+      if (Instruction *I = dyn_cast<Instruction>(incoming))
+        if (!L->makeLoopInvariant(I, Changed, Preheader->getTerminator())) {
+          AllEntriesInvariant = false;
+          break;
+        }
+    }
   }
 
   if (Changed)
@@ -193,7 +195,7 @@
   // be in the situation of needing to be able to solve statically which exit
   // block will be branched to, or trying to preserve the branching logic in
   // a loop invariant manner.
-  if (!ExitBlock) {
+  if (!ExitBlock && L->getNumExitBlocks() != 0) {
     LLVM_DEBUG(dbgs() << "Deletion requires single exit block\n");
     return LoopDeletionResult::Unmodified;
   }
@@ -208,8 +210,10 @@
   // Don't remove loops for which we can't solve the trip count.
   // They could be infinite, in which case we'd be changing program behavior.
   const SCEV *S = SE.getConstantMaxBackedgeTakenCount(L);
-  if (isa<SCEVCouldNotCompute>(S)) {
-    LLVM_DEBUG(dbgs() << "Could not compute SCEV MaxBackedgeTakenCount.\n");
+  if (isa<SCEVCouldNotCompute>(S) &&
+      !L->getHeader()->getParent()->mustProgress() && !hasMustProgress(L)) {
+    LLVM_DEBUG(dbgs() << "Could not compute SCEV MaxBackedgeTakenCount and was "
+                         "not required to make progress.\n");
     return Changed ? LoopDeletionResult::Modified
                    : LoopDeletionResult::Unmodified;
   }
diff --git a/llvm/lib/Transforms/Utils/LoopUtils.cpp b/llvm/lib/Transforms/Utils/LoopUtils.cpp
--- a/llvm/lib/Transforms/Utils/LoopUtils.cpp
+++ b/llvm/lib/Transforms/Utils/LoopUtils.cpp
@@ -63,6 +63,7 @@
 
 static const char *LLVMLoopDisableNonforced = "llvm.loop.disable_nonforced";
 static const char *LLVMLoopDisableLICM = "llvm.licm.disable";
+static const char *LLVMLoopMustProgress = "llvm.loop.mustprogress";
 
 bool llvm::formDedicatedExitBlocks(Loop *L, DominatorTree *DT, LoopInfo *LI,
                                    MemorySSAUpdater *MSSAU,
@@ -404,6 +405,10 @@
   return getBooleanLoopAttribute(L, LLVMLoopDisableLICM);
 }
 
+bool llvm::hasMustProgress(const Loop *L) {
+  return getBooleanLoopAttribute(L, LLVMLoopMustProgress);
+}
+
 TransformationMode llvm::hasUnrollTransformation(Loop *L) {
   if (getBooleanLoopAttribute(L, "llvm.loop.unroll.disable"))
     return TM_SuppressedByUser;
@@ -542,10 +547,6 @@
   if (SE)
     SE->forgetLoop(L);
 
-  auto *ExitBlock = L->getUniqueExitBlock();
-  assert(ExitBlock && "Should have a unique exit block!");
-  assert(L->hasDedicatedExits() && "Loop should have dedicated exits!");
-
   auto *OldBr = dyn_cast<BranchInst>(Preheader->getTerminator());
   assert(OldBr && "Preheader must end with a branch");
   assert(OldBr->isUnconditional() && "Preheader must have a single successor");
@@ -575,59 +576,73 @@
   // deleting the backedge of the outer loop). If the outer loop is indeed a
   // non-loop, it will be deleted in a future iteration of loop deletion pass.
   IRBuilder<> Builder(OldBr);
-  Builder.CreateCondBr(Builder.getFalse(), L->getHeader(), ExitBlock);
-  // Remove the old branch. The conditional branch becomes a new terminator.
-  OldBr->eraseFromParent();
-
-  // Rewrite phis in the exit block to get their inputs from the Preheader
-  // instead of the exiting block.
-  for (PHINode &P : ExitBlock->phis()) {
-    // Set the zero'th element of Phi to be from the preheader and remove all
-    // other incoming values. Given the loop has dedicated exits, all other
-    // incoming values must be from the exiting blocks.
-    int PredIndex = 0;
-    P.setIncomingBlock(PredIndex, Preheader);
-    // Removes all incoming values from all other exiting blocks (including
-    // duplicate values from an exiting block).
-    // Nuke all entries except the zero'th entry which is the preheader entry.
-    // NOTE! We need to remove Incoming Values in the reverse order as done
-    // below, to keep the indices valid for deletion (removeIncomingValues
-    // updates getNumIncomingValues and shifts all values down into the operand
-    // being deleted).
-    for (unsigned i = 0, e = P.getNumIncomingValues() - 1; i != e; ++i)
-      P.removeIncomingValue(e - i, false);
-
-    assert((P.getNumIncomingValues() == 1 &&
-            P.getIncomingBlock(PredIndex) == Preheader) &&
-           "Should have exactly one value and that's from the preheader!");
-  }
 
-  DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Eager);
-  if (DT) {
-    DTU.applyUpdates({{DominatorTree::Insert, Preheader, ExitBlock}});
-    if (MSSA) {
-      MSSAU->applyUpdates({{DominatorTree::Insert, Preheader, ExitBlock}}, *DT);
-      if (VerifyMemorySSA)
-        MSSA->verifyMemorySSA();
+  auto *ExitBlock = L->getUniqueExitBlock();
+  if (L->getNumExitBlocks() == 0) {
+    // If this loop does not have an exit block, we can still remove the loop
+    // and replace the Preheader with an Unreachable.
+    Builder.SetInsertPoint(OldBr);
+    Builder.CreateUnreachable();
+    Preheader->getTerminator()->eraseFromParent();
+  } else {
+    assert(ExitBlock && "Should have a unique exit block!");
+    assert(L->hasDedicatedExits() && "Loop should have dedicated exits!");
+
+    Builder.CreateCondBr(Builder.getFalse(), L->getHeader(), ExitBlock);
+    // Remove the old branch. The conditional branch becomes a new terminator.
+    OldBr->eraseFromParent();
+
+    // Rewrite phis in the exit block to get their inputs from the Preheader
+    // instead of the exiting block.
+    for (PHINode &P : ExitBlock->phis()) {
+      // Set the zero'th element of Phi to be from the preheader and remove all
+      // other incoming values. Given the loop has dedicated exits, all other
+      // incoming values must be from the exiting blocks.
+      int PredIndex = 0;
+      P.setIncomingBlock(PredIndex, Preheader);
+      // Removes all incoming values from all other exiting blocks (including
+      // duplicate values from an exiting block).
+      // Nuke all entries except the zero'th entry which is the preheader entry.
+      // NOTE! We need to remove Incoming Values in the reverse order as done
+      // below, to keep the indices valid for deletion (removeIncomingValues
+      // updates getNumIncomingValues and shifts all values down into the
+      // operand being deleted).
+      for (unsigned i = 0, e = P.getNumIncomingValues() - 1; i != e; ++i)
+        P.removeIncomingValue(e - i, false);
+
+      assert((P.getNumIncomingValues() == 1 &&
+              P.getIncomingBlock(PredIndex) == Preheader) &&
+             "Should have exactly one value and that's from the preheader!");
+    }
+
+    DomTreeUpdater DTU(DT, DomTreeUpdater::UpdateStrategy::Eager);
+    if (DT) {
+      DTU.applyUpdates({{DominatorTree::Insert, Preheader, ExitBlock}});
+      if (MSSA) {
+        MSSAU->applyUpdates({{DominatorTree::Insert, Preheader, ExitBlock}},
+                            *DT);
+        if (VerifyMemorySSA)
+          MSSA->verifyMemorySSA();
+      }
     }
-  }
 
-  // Disconnect the loop body by branching directly to its exit.
-  Builder.SetInsertPoint(Preheader->getTerminator());
-  Builder.CreateBr(ExitBlock);
-  // Remove the old branch.
-  Preheader->getTerminator()->eraseFromParent();
-
-  if (DT) {
-    DTU.applyUpdates({{DominatorTree::Delete, Preheader, L->getHeader()}});
-    if (MSSA) {
-      MSSAU->applyUpdates({{DominatorTree::Delete, Preheader, L->getHeader()}},
-                          *DT);
-      SmallSetVector<BasicBlock *, 8> DeadBlockSet(L->block_begin(),
-                                                   L->block_end());
-      MSSAU->removeBlocks(DeadBlockSet);
-      if (VerifyMemorySSA)
-        MSSA->verifyMemorySSA();
+    // Disconnect the loop body by branching directly to its exit.
+    Builder.SetInsertPoint(Preheader->getTerminator());
+    Builder.CreateBr(ExitBlock);
+    // Remove the old branch.
+    Preheader->getTerminator()->eraseFromParent();
+
+    if (DT) {
+      DTU.applyUpdates({{DominatorTree::Delete, Preheader, L->getHeader()}});
+      if (MSSA) {
+        MSSAU->applyUpdates(
+            {{DominatorTree::Delete, Preheader, L->getHeader()}}, *DT);
+        SmallSetVector<BasicBlock *, 8> DeadBlockSet(L->block_begin(),
+                                                     L->block_end());
+        MSSAU->removeBlocks(DeadBlockSet);
+        if (VerifyMemorySSA)
+          MSSA->verifyMemorySSA();
+      }
     }
   }
 
@@ -674,15 +689,17 @@
   // Since debug values in the loop have been deleted, inserting an undef
   // dbg.value truncates the range of any dbg.value before the loop where the
   // loop used to be. This is particularly important for constant values.
-  DIBuilder DIB(*ExitBlock->getModule());
-  Instruction *InsertDbgValueBefore = ExitBlock->getFirstNonPHI();
-  assert(InsertDbgValueBefore &&
-         "There should be a non-PHI instruction in exit block, else these "
-         "instructions will have no parent.");
-  for (auto *DVI : DeadDebugInst)
-    DIB.insertDbgValueIntrinsic(UndefValue::get(Builder.getInt32Ty()),
-                                DVI->getVariable(), DVI->getExpression(),
-                                DVI->getDebugLoc(), InsertDbgValueBefore);
+  if (ExitBlock) {
+    DIBuilder DIB(*ExitBlock->getModule());
+    Instruction *InsertDbgValueBefore = ExitBlock->getFirstNonPHI();
+    assert(InsertDbgValueBefore &&
+           "There should be a non-PHI instruction in exit block, else these "
+           "instructions will have no parent.");
+    for (auto *DVI : DeadDebugInst)
+      DIB.insertDbgValueIntrinsic(UndefValue::get(Builder.getInt32Ty()),
+                                  DVI->getVariable(), DVI->getExpression(),
+                                  DVI->getDebugLoc(), InsertDbgValueBefore);
+  }
 
   // Remove the block from the reference counting scheme, so that we can
   // delete it freely later.
diff --git a/llvm/test/Other/loop-deletion-printer.ll b/llvm/test/Other/loop-deletion-printer.ll
--- a/llvm/test/Other/loop-deletion-printer.ll
+++ b/llvm/test/Other/loop-deletion-printer.ll
@@ -14,7 +14,7 @@
 ; DELETED-BUT-PRINTED: IR Dump {{.*}}LoopDeletionPass {{.*invalidated:}}
 ; DELETED-BUT-PRINTED-NOT: IR Dump {{.*}}LoopInstSimplifyPass
 
-define void @deleteme() {
+define void @deleteme() willreturn {
 entry:
   br label %loop
 loop:
diff --git a/llvm/test/Other/loop-pm-invalidation.ll b/llvm/test/Other/loop-pm-invalidation.ll
--- a/llvm/test/Other/loop-pm-invalidation.ll
+++ b/llvm/test/Other/loop-pm-invalidation.ll
@@ -227,7 +227,7 @@
   ret void
 }
 
-define void @dead_loop() {
+define void @dead_loop() willreturn {
 ; CHECK-LOOP-INV: Starting {{.*}}Function pass manager run
 ; CHECK-LOOP-INV-NEXT: Starting {{.*}}Function pass manager run
 ; CHECK-LOOP-INV-NEXT: Running pass: LoopSimplifyPass
diff --git a/llvm/test/Transforms/LICM/2003-02-27-PreheaderProblem.ll b/llvm/test/Transforms/LICM/2003-02-27-PreheaderProblem.ll
--- a/llvm/test/Transforms/LICM/2003-02-27-PreheaderProblem.ll
+++ b/llvm/test/Transforms/LICM/2003-02-27-PreheaderProblem.ll
@@ -6,7 +6,7 @@
 ; RUN: opt < %s -licm -loop-deletion -simplifycfg -S | \
 ; RUN:   not grep "br "
 
-define i32 @main(i32 %argc) {
+define i32 @main(i32 %argc) willreturn {
 ; <label>:0
 	br label %bb5
 bb5:		; preds = %bb5, %0
diff --git a/llvm/test/Transforms/LoopDeletion/2017-07-11-incremental-dt.ll b/llvm/test/Transforms/LoopDeletion/2017-07-11-incremental-dt.ll
--- a/llvm/test/Transforms/LoopDeletion/2017-07-11-incremental-dt.ll
+++ b/llvm/test/Transforms/LoopDeletion/2017-07-11-incremental-dt.ll
@@ -14,7 +14,7 @@
 ; DT:     [3] %for.body
 ; DT:       [4] %for.cond3.loopexit
 
-define i32 @fn1() {
+define i32 @fn1() willreturn {
 entry:
   br label %for.cond
 
diff --git a/llvm/test/Transforms/LoopDeletion/basic-remark.ll b/llvm/test/Transforms/LoopDeletion/basic-remark.ll
--- a/llvm/test/Transforms/LoopDeletion/basic-remark.ll
+++ b/llvm/test/Transforms/LoopDeletion/basic-remark.ll
@@ -10,7 +10,7 @@
 ; CHECK-NEXT: Args:
 ; CHECK-NEXT:   - String:          Loop deleted because it is invariant
 ; CHECK-NEXT: ...
-define i32 @main() local_unnamed_addr #0 {
+define i32 @main() local_unnamed_addr willreturn {
 entry:
   br label %for.cond, !dbg !9
 
diff --git a/llvm/test/Transforms/LoopDeletion/diundef.ll b/llvm/test/Transforms/LoopDeletion/diundef.ll
--- a/llvm/test/Transforms/LoopDeletion/diundef.ll
+++ b/llvm/test/Transforms/LoopDeletion/diundef.ll
@@ -5,7 +5,7 @@
 
 @a = common local_unnamed_addr global i32 0, align 4, !dbg !0
 
-define i32 @b() local_unnamed_addr !dbg !12 {
+define i32 @b() local_unnamed_addr willreturn !dbg !12 {
 entry:
   call void @llvm.dbg.value(metadata i32 0, metadata !16, metadata !DIExpression()), !dbg !17
   br label %for.cond, !dbg !18
diff --git a/llvm/test/Transforms/LoopDeletion/invalidation.ll b/llvm/test/Transforms/LoopDeletion/invalidation.ll
--- a/llvm/test/Transforms/LoopDeletion/invalidation.ll
+++ b/llvm/test/Transforms/LoopDeletion/invalidation.ll
@@ -8,7 +8,7 @@
 ; RUN:     | FileCheck %s --check-prefixes=CHECK,AFTER
 
 
-define void @foo(i64 %n, i64 %m) nounwind {
+define void @foo(i64 %n, i64 %m) nounwind willreturn {
 ; CHECK-LABEL: @foo(
 
 entry:
diff --git a/llvm/test/Transforms/LoopDeletion/multiple-exit-conditions.ll b/llvm/test/Transforms/LoopDeletion/multiple-exit-conditions.ll
--- a/llvm/test/Transforms/LoopDeletion/multiple-exit-conditions.ll
+++ b/llvm/test/Transforms/LoopDeletion/multiple-exit-conditions.ll
@@ -11,7 +11,7 @@
 ; CHECK:      return:
 ; CHECK-NEXT:   ret void
 
-define void @foo(i64 %n, i64 %m) nounwind {
+define void @foo(i64 %n, i64 %m) nounwind willreturn {
 entry:
   br label %bb
 
diff --git a/llvm/test/Transforms/LoopDeletion/multiple-exits.ll b/llvm/test/Transforms/LoopDeletion/multiple-exits.ll
--- a/llvm/test/Transforms/LoopDeletion/multiple-exits.ll
+++ b/llvm/test/Transforms/LoopDeletion/multiple-exits.ll
@@ -10,7 +10,7 @@
 ; RUN: opt < %s -passes=loop-deletion -S | FileCheck %s --check-prefixes=CHECK,AFTER
 
 
-define void @foo(i64 %n, i64 %m) nounwind {
+define void @foo(i64 %n, i64 %m) #0 {
 ; CHECK-LABEL: @foo(
 
 entry:
@@ -43,7 +43,7 @@
 ; CHECK-NEXT:    ret void
 }
 
-define i64 @bar(i64 %n, i64 %m, i64 %maybe_zero) nounwind {
+define i64 @bar(i64 %n, i64 %m, i64 %maybe_zero) #0 {
 ; CHECK-LABEL: @bar(
 
 entry:
@@ -95,7 +95,7 @@
 
 ; This function has a loop which looks like @bar's but that cannot be deleted
 ; because which path we exit through determines which value is selected.
-define i64 @baz(i64 %n, i64 %m, i64 %maybe_zero) nounwind {
+define i64 @baz(i64 %n, i64 %m, i64 %maybe_zero) #0 {
 ; CHECK-LABEL:  @baz(
 
 entry:
@@ -136,3 +136,5 @@
 ; CHECK-NEXT:  %[[X:.*]] = phi i64 [ 12, %bb ], [ 10, %bb2 ], [ 10, %bb3 ]
 ; CHECK-NEXT:  ret i64 %[[X]]
 }
+
+attributes #0 = { nounwind willreturn }
\ No newline at end of file
diff --git a/llvm/test/Transforms/LoopDeletion/mustprogress.ll b/llvm/test/Transforms/LoopDeletion/mustprogress.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/Transforms/LoopDeletion/mustprogress.ll
@@ -0,0 +1,237 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --function-signature --check-attributes
+; RUN: opt < %s -loop-deletion -S | FileCheck %s
+
+;; Original C Code:
+;;  void unknown_tripcount_mustprogress_attr_mustprogress_loopmd(int a, int b) {
+;;    for (; a < b;) ;
+;;    for (;;) ;
+;;  }
+
+define void @unknown_tripcount_mustprogress_attr_mustprogress_loopmd(i32 %a, i32 %b) #0 {
+; CHECK: Function Attrs: mustprogress
+; CHECK-LABEL: define {{[^@]+}}@unknown_tripcount_mustprogress_attr_mustprogress_loopmd
+; CHECK-SAME: (i32 [[A:%.*]], i32 [[B:%.*]]) [[ATTR0:#.*]] {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[FOR_END:%.*]]
+; CHECK:       for.end:
+; CHECK-NEXT:    unreachable
+;
+entry:
+  br label %for.cond
+for.cond:
+  %cmp = icmp slt i32 %a, %b
+  br i1 %cmp, label %for.body, label %for.end
+for.body:
+  br label %for.cond, !llvm.loop !2
+for.end:
+  br label %for.cond1
+for.cond1:
+  br label %for.cond1
+}
+
+;; Original C Code:
+;;  void unknown_tripcount_mustprogress_attr_no_mustprogress_loopmd(int a, int b) {
+;;    for (; a < b;) ;
+;;    for (;;) ;
+;;  }
+;;  => Removed mustprogress loop attribute
+
+define void @unknown_tripcount_mustprogress_attr_no_mustprogess_loopmd(i32 %a, i32 %b) #0 {
+; CHECK: Function Attrs: mustprogress
+; CHECK-LABEL: define {{[^@]+}}@unknown_tripcount_mustprogress_attr_no_mustprogess_loopmd
+; CHECK-SAME: (i32 [[A:%.*]], i32 [[B:%.*]]) [[ATTR0]] {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[FOR_END:%.*]]
+; CHECK:       for.end:
+; CHECK-NEXT:    unreachable
+;
+entry:
+  br label %for.cond
+for.cond:
+  %cmp = icmp slt i32 %a, %b
+  br i1 %cmp, label %for.body, label %for.end
+for.body:
+  br label %for.cond
+for.end:
+  br label %for.cond1
+for.cond1:
+  br label %for.cond1
+}
+
+;; Original C Code:
+;;  void known_tripcount_no_mustprogress_attr_no_mustprogress_loopmd() {
+;;    for (int i = 0; i < 5; i++) ;
+;;  }
+
+define void @known_tripcount_no_mustprogress_attr_no_mustprogress_loopmd() {
+; CHECK-LABEL: define {{[^@]+}}@known_tripcount_no_mustprogress_attr_no_mustprogress_loopmd() {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[FOR_END:%.*]]
+; CHECK:       for.end:
+; CHECK-NEXT:    ret void
+;
+entry:
+  br label %for.cond
+for.cond:
+  %i.0 = phi i32 [ 0, %entry ], [ %inc, %for.inc ]
+  %cmp = icmp slt i32 %i.0, 5
+  br i1 %cmp, label %for.body, label %for.end
+for.body:
+  br label %for.inc
+for.inc:
+  %inc = add nsw i32 %i.0, 1
+  br label %for.cond
+for.end:
+  ret void
+}
+
+;; Original C Code:
+;;  void known_tripcount_no_mustprogress_attr_mustprogress_loopmd() {
+;;    for (int i = 0; i < 5; i++) ;
+;;  }
+;;  => Added mustprogress loop attribute
+
+define void @known_tripcount_no_mustprogress_attr_mustprogress_loopmd() {
+; CHECK-LABEL: define {{[^@]+}}@known_tripcount_no_mustprogress_attr_mustprogress_loopmd() {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[FOR_END:%.*]]
+; CHECK:       for.end:
+; CHECK-NEXT:    ret void
+;
+entry:
+  br label %for.cond
+for.cond:
+  %i.0 = phi i32 [ 0, %entry ], [ %inc, %for.inc ]
+  %cmp = icmp slt i32 %i.0, 5
+  br i1 %cmp, label %for.body, label %for.end
+for.body:
+  br label %for.inc
+for.inc:
+  %inc = add nsw i32 %i.0, 1
+  br label %for.cond, !llvm.loop !4
+for.end:
+  ret void
+}
+
+;; Original C Code:
+;;  void known_tripcount_mustprogress_attr_no_mustprogress_loopmd() {
+;;    for (int i = 0; i < 5; i++) ;
+;;  }
+;;  => Added mustprogress function attribute
+
+define void @known_tripcount_mustprogress_attr_no_mustprogress_loopmd() #0 {
+; CHECK: Function Attrs: mustprogress
+; CHECK-LABEL: define {{[^@]+}}@known_tripcount_mustprogress_attr_no_mustprogress_loopmd
+; CHECK-SAME: () [[ATTR0]] {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[FOR_END:%.*]]
+; CHECK:       for.end:
+; CHECK-NEXT:    ret void
+;
+entry:
+  br label %for.cond
+for.cond:
+  %i.0 = phi i32 [ 0, %entry ], [ %inc, %for.inc ]
+  %cmp = icmp slt i32 %i.0, 5
+  br i1 %cmp, label %for.body, label %for.end
+for.body:
+  br label %for.inc
+for.inc:
+  %inc = add nsw i32 %i.0, 1
+  br label %for.cond
+for.end:
+  ret void
+}
+
+;; Original C Code:
+;;  void known_tripcount_mustprogress_attr_mustprogress_loopmd() {
+;;    for (int i = 0; i < 5; i++) ;
+;;  }
+;;  => Added mustprogress function and mustprogress loop attribute
+
+define void @known_tripcount_mustprogress_attr_mustprogress_loopmd() #0 {
+; CHECK: Function Attrs: mustprogress
+; CHECK-LABEL: define {{[^@]+}}@known_tripcount_mustprogress_attr_mustprogress_loopmd
+; CHECK-SAME: () [[ATTR0]] {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[FOR_END:%.*]]
+; CHECK:       for.end:
+; CHECK-NEXT:    ret void
+;
+entry:
+  br label %for.cond
+for.cond:
+  %i.0 = phi i32 [ 0, %entry ], [ %inc, %for.inc ]
+  %cmp = icmp slt i32 %i.0, 5
+  br i1 %cmp, label %for.body, label %for.end
+for.body:
+  br label %for.inc
+for.inc:
+  %inc = add nsw i32 %i.0, 1
+  br label %for.cond, !llvm.loop !5
+for.end:
+  ret void
+}
+
+;; Original C Code:
+;;  void unknown_tripcount_no_mustprogress_attr_mustprogress_loopmd(int a, int b) {
+;;    for (; a < b;) ;
+;;  }
+;;  => Added mustprogress loop attribute
+
+define void @unknown_tripcount_no_mustprogress_attr_mustprogress_loopmd(i32 %a, i32 %b) {
+; CHECK-LABEL: define {{[^@]+}}@unknown_tripcount_no_mustprogress_attr_mustprogress_loopmd
+; CHECK-SAME: (i32 [[A:%.*]], i32 [[B:%.*]]) {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[FOR_END:%.*]]
+; CHECK:       for.end:
+; CHECK-NEXT:    ret void
+;
+entry:
+  br label %for.cond
+for.cond:
+  %cmp = icmp slt i32 %a, %b
+  br i1 %cmp, label %for.body, label %for.end
+for.body:
+  br label %for.cond, !llvm.loop !6
+for.end:
+  ret void
+}
+
+;; Original C Code:
+;;  void unknown_tripcount_no_mustprogress_attr_no_mustprogress_loopmd(int a, int b) {
+;;    for (; a < b;) ;
+;;  }
+
+define void @unknown_tripcount_no_mustprogress_attr_no_mustprogress_loopmd(i32 %a, i32 %b) {
+; CHECK-LABEL: define {{[^@]+}}@unknown_tripcount_no_mustprogress_attr_no_mustprogress_loopmd
+; CHECK-SAME: (i32 [[A:%.*]], i32 [[B:%.*]]) {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[FOR_COND:%.*]]
+; CHECK:       for.cond:
+; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i32 [[A]], [[B]]
+; CHECK-NEXT:    br i1 [[CMP]], label [[FOR_BODY:%.*]], label [[FOR_END:%.*]]
+; CHECK:       for.body:
+; CHECK-NEXT:    br label [[FOR_COND]]
+; CHECK:       for.end:
+; CHECK-NEXT:    ret void
+;
+entry:
+  br label %for.cond
+for.cond:
+  %cmp = icmp slt i32 %a, %b
+  br i1 %cmp, label %for.body, label %for.end
+for.body:
+  br label %for.cond
+for.end:
+  ret void
+}
+
+; CHECK: attributes [[ATTR0]] = { mustprogress }
+
+attributes #0 = { mustprogress }
+!2 = distinct !{!2, !3}
+!3 = !{!"llvm.loop.mustprogress"}
+!4 = distinct !{!4, !3}
+!5 = distinct !{!5, !3}
+!6 = distinct !{!6, !3}
diff --git a/llvm/test/Transforms/LoopDeletion/unreachable-loops.ll b/llvm/test/Transforms/LoopDeletion/unreachable-loops.ll
--- a/llvm/test/Transforms/LoopDeletion/unreachable-loops.ll
+++ b/llvm/test/Transforms/LoopDeletion/unreachable-loops.ll
@@ -216,7 +216,7 @@
 ; Show recursive deletion of loops. Since we start with subloops and progress outward 
 ; to parent loop, we first delete the loop L2. Now loop L1 becomes a non-loop since it's backedge
 ; from L2's preheader to L1's exit block is never taken. So, L1 gets deleted as well.
-define void @test8(i64 %n) {
+define void @test8(i64 %n) #0 {
 ; CHECK-LABEL: test8
 ; CHECK-LABEL: entry:
 ; CHECK-NEXT: br label %exit
@@ -318,7 +318,7 @@
 ; deleted.
 ; In the next iteration, since L2 is never executed and has no subloops, we delete
 ; L2 as well. Finally, the outermost loop L1 is deleted.
-define void @test11(i64 %n) {
+define void @test11(i64 %n) #0 {
 ; CHECK-LABEL: test11
 ; CHECK-LABEL: entry:
 ; CHECK-NEXT: br label %exit
@@ -355,7 +355,7 @@
 
 
 ; 2 edges from a single exiting block to the exit block.
-define i64 @test12(i64 %n){
+define i64 @test12(i64 %n) #0 {
 ;CHECK-LABEL: @test12
 ; CHECK-NOT: L1:
 ; CHECK-NOT: L1Latch:
@@ -392,7 +392,7 @@
 }
 
 ; multiple edges to exit block from the same exiting blocks
-define i64 @test13(i64 %n) {
+define i64 @test13(i64 %n) #0 {
 ; CHECK-LABEL: @test13
 ; CHECK-NOT: L1:
 ; CHECK-NOT: L1Latch:
@@ -433,3 +433,5 @@
   %y.phi = phi i64 [ 10, %L1Block ], [ 10, %L1Block ], [ %y.next, %L1 ], [ 30, %L1Latch ], [ 30, %L1Latch ]
   ret i64 %y.phi
 }
+
+attributes #0 = { willreturn }
diff --git a/llvm/test/Transforms/LoopDeletion/use-in-unreachable.ll b/llvm/test/Transforms/LoopDeletion/use-in-unreachable.ll
--- a/llvm/test/Transforms/LoopDeletion/use-in-unreachable.ll
+++ b/llvm/test/Transforms/LoopDeletion/use-in-unreachable.ll
@@ -3,7 +3,7 @@
 ; Checking that possible users of instruction from the loop in
 ; unreachable blocks are handled.
 
-define i64 @foo() {
+define i64 @foo() willreturn {
 entry:
   br label %invloop
 ; CHECK-LABEL-NOT: invloop
diff --git a/llvm/test/Transforms/SCCP/calltest.ll b/llvm/test/Transforms/SCCP/calltest.ll
--- a/llvm/test/Transforms/SCCP/calltest.ll
+++ b/llvm/test/Transforms/SCCP/calltest.ll
@@ -4,7 +4,7 @@
 %empty = type {}
 declare %empty @has_side_effects()
 
-define double @test_0(i32 %param) {
+define double @test_0(i32 %param) willreturn {
 ; CHECK-LABEL: @test_0(
 ; CHECK-NOT: br
 entry:
diff --git a/llvm/test/Transforms/SimpleLoopUnswitch/pr37888.ll b/llvm/test/Transforms/SimpleLoopUnswitch/pr37888.ll
--- a/llvm/test/Transforms/SimpleLoopUnswitch/pr37888.ll
+++ b/llvm/test/Transforms/SimpleLoopUnswitch/pr37888.ll
@@ -7,7 +7,7 @@
 
 target triple = "x86_64-unknown-linux-gnu"
 
-define void @pr37888() {
+define void @pr37888() willreturn {
 ; CHECK-LABEL: define void @pr37888()
 entry:
   %tobool = icmp ne i16 undef, 0