Index: lib/Transforms/Scalar/IndVarSimplify.cpp
===================================================================
--- lib/Transforms/Scalar/IndVarSimplify.cpp
+++ lib/Transforms/Scalar/IndVarSimplify.cpp
@@ -2737,12 +2737,72 @@
       Changed = true;
       continue;
     }
+  }
+
+  // @Reviewers: This block of code is a literally copy from D68956, and would
+  // of course be rebased over that.  Please ignore for the moment.
+  llvm::sort(ExitingBlocks,
+           [&](BasicBlock *A, BasicBlock *B) {
+               // std::sort sorts in ascending order, so we want the inverse of
+               // the normal dominance relation, plus a tie breaker for blocks
+               // unordered by dominance.
+               if (DT->properlyDominates(A, B)) return true;
+               if (DT->properlyDominates(B, A)) return false;
+               return A->getName() < B->getName();
+             });
+  for (unsigned i = 1; i < ExitingBlocks.size(); i++)
+    if (!DT->dominates(ExitingBlocks[i-1], ExitingBlocks[i]))
+      return false;
+
+  SmallSet<const SCEV*, 8> DominatingExitCounts;
+  for (BasicBlock *ExitingBB : ExitingBlocks) {
+    // If our exitting block exits multiple loops, we can only rewrite the
+    // innermost one.  Otherwise, we're changing how many times the innermost
+    // loop runs before it exits. 
+    if (LI->getLoopFor(ExitingBB) != L)
+      continue;
+
+    // Can't rewrite non-branch yet.
+    BranchInst *BI = dyn_cast<BranchInst>(ExitingBB->getTerminator());
+    if (!BI)
+      continue;
 
-    // TODO: If we can prove that the exiting iteration is equal to the exit
-    // count for this exit and that no previous exit oppurtunities exist within
-    // the loop, then we can discharge all other exits.  (May fall out of
-    // previous TODO.)
+    // If already constant, nothing to do.
+    if (isa<Constant>(BI->getCondition()))
+      continue;
+    
+    const SCEV *ExitCount = SE->getExitCount(L, ExitingBB);
+    if (isa<SCEVCouldNotCompute>(ExitCount))
+      continue;
+
+    // If we end up with a pointer exit count, bail.  Note that we can end up
+    // with a pointer exit count for one exiting block, and not for another in
+    // the same loop.
+    if (!ExitCount->getType()->isIntegerTy())
+      continue;
+
+    // We want x and zext(x) to map to the same values..
+    Type *WiderType =
+      SE->getWiderType(MaxExitCount->getType(), ExitCount->getType());
+    ExitCount = SE->getNoopOrZeroExtend(ExitCount, WiderType);
+
+    // As we run, keep track of which exit counts we've encountered an exit
+    // which dominates the successive exits.  If we find a duplicate, we've
+    // found an exit which would have exited on the exiting iteration, but
+    // strictly follows another which does the same and is thus dead.
+    if (!DominatingExitCounts.insert(ExitCount).second) {
+      bool ExitIfTrue = !L->contains(*succ_begin(ExitingBB));
+      auto *OldCond = BI->getCondition();
+      auto *NewCond = ExitIfTrue ? ConstantInt::getFalse(OldCond->getType()) :
+        ConstantInt::getTrue(OldCond->getType());
+      BI->setCondition(NewCond);
+      if (OldCond->use_empty())
+        DeadInsts.push_back(OldCond);
+      Changed = true;
+      continue;
+    }
   }
+  
 
   // Finally, see if we can rewrite our exit conditions into a loop invariant
   // form.  If we have a read-only loop, and we can tell that we must exit down
Index: test/Transforms/IndVarSimplify/eliminate-exit.ll
===================================================================
--- test/Transforms/IndVarSimplify/eliminate-exit.ll
+++ test/Transforms/IndVarSimplify/eliminate-exit.ll
@@ -185,5 +185,39 @@
   ret void
 }
 
+define void @mixed_width(i32 %len) {
+; CHECK-LABEL: @mixed_width(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[LEN_ZEXT:%.*]] = zext i32 [[LEN:%.*]] to i64
+; CHECK-NEXT:    br label [[LOOP:%.*]]
+; CHECK:       loop:
+; CHECK-NEXT:    [[IV:%.*]] = phi i64 [ 0, [[ENTRY:%.*]] ], [ [[IV_NEXT:%.*]], [[BACKEDGE:%.*]] ]
+; CHECK-NEXT:    [[IV_NEXT]] = add nuw nsw i64 [[IV]], 1
+; CHECK-NEXT:    [[CMP1:%.*]] = icmp ult i64 [[IV]], [[LEN_ZEXT]]
+; CHECK-NEXT:    br i1 [[CMP1]], label [[BACKEDGE]], label [[EXIT:%.*]]
+; CHECK:       backedge:
+; CHECK-NEXT:    call void @side_effect()
+; CHECK-NEXT:    br i1 true, label [[LOOP]], label [[EXIT]]
+; CHECK:       exit:
+; CHECK-NEXT:    ret void
+;
+entry:
+  %len.zext = zext i32 %len to i64
+  br label %loop
+loop:
+  %iv = phi i64 [0, %entry], [%iv.next, %backedge]
+  %iv2 = phi i32 [0, %entry], [%iv2.next, %backedge]
+  %iv.next = add i64 %iv, 1
+  %iv2.next = add i32 %iv2, 1
+  %cmp1 = icmp ult i64 %iv, %len.zext
+  br i1 %cmp1, label %backedge, label %exit
+
+backedge:
+  call void @side_effect()
+  %cmp2 = icmp ult i32 %iv2, %len
+  br i1 %cmp2, label %loop, label %exit
+exit:
+  ret void
+}
 
 declare void @side_effect()