diff --git a/llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp b/llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
--- a/llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopIdiomRecognize.cpp
@@ -1475,6 +1475,7 @@
     return false;
 
   // step 4: Find the instruction which count the CTLZ: cnt.next = cnt + 1
+  //         or cnt.next = cnt + -1.
   // TODO: We can skip the step. If loop trip count is known (CTLZ),
   //       then all uses of "cnt.next" could be optimized to the trip count
   //       plus "cnt0". Currently it is not optimized.
@@ -1488,7 +1489,7 @@
       continue;
 
     ConstantInt *Inc = dyn_cast<ConstantInt>(Inst->getOperand(1));
-    if (!Inc || !Inc->isOne())
+    if (!Inc || (!Inc->isOne() && !Inc->isMinusOne()))
       continue;
 
     PHINode *Phi = getRecurrenceVar(Inst->getOperand(0), Inst, LoopEntry);
@@ -1751,11 +1752,18 @@
   NewCount = Builder.CreateZExtOrTrunc(NewCount,
                                        cast<IntegerType>(CntInst->getType()));
 
-  // If the counter's initial value is not zero, insert Add Inst.
   Value *CntInitVal = CntPhi->getIncomingValueForBlock(Preheader);
-  ConstantInt *InitConst = dyn_cast<ConstantInt>(CntInitVal);
-  if (!InitConst || !InitConst->isZero())
-    NewCount = Builder.CreateAdd(NewCount, CntInitVal);
+  if (cast<ConstantInt>(CntInst->getOperand(1))->isOne()) {
+    // If the counter was being incremented in the loop, add NewCount to the
+    // counter's initial value, but only if the initial value is not zero.
+    ConstantInt *InitConst = dyn_cast<ConstantInt>(CntInitVal);
+    if (!InitConst || !InitConst->isZero())
+      NewCount = Builder.CreateAdd(NewCount, CntInitVal);
+  } else {
+    // If the count was being decremented in the loop, subract NewCount from the
+    // counter's initial value.
+    NewCount = Builder.CreateSub(CntInitVal, NewCount);
+  }
 
   // Step 2: Insert new IV and loop condition:
   // loop:
diff --git a/llvm/test/Transforms/LoopIdiom/X86/ctlz.ll b/llvm/test/Transforms/LoopIdiom/X86/ctlz.ll
--- a/llvm/test/Transforms/LoopIdiom/X86/ctlz.ll
+++ b/llvm/test/Transforms/LoopIdiom/X86/ctlz.ll
@@ -526,3 +526,89 @@
 while.end:                                        ; preds = %while.cond
   ret i32 %inc
 }
+
+; Recognize CTLZ builtin pattern.
+; Here it will replace the loop -
+; assume builtin is always profitable.
+;
+; int ctlz_decrement(int n)
+; {
+;   int i = 32;
+;   while(n) {
+;     n >>= 1;
+;     i--;
+;   }
+;   return i;
+; }
+;
+; ALL:  entry
+; ALL:  %0 = call i32 @llvm.ctlz.i32(i32 %n, i1 true)
+; ALL-NEXT:  %1 = sub i32 32, %0
+; ALL-NEXT:  %2 = sub i32 32, %1
+; ALL:  %inc.lcssa = phi i32 [ %2, %while.body ]
+; ALL:  %i.0.lcssa = phi i32 [ 32, %entry ], [ %inc.lcssa, %while.end.loopexit ]
+; ALL:  ret i32 %i.0.lcssa
+
+; Function Attrs: norecurse nounwind readnone uwtable
+define i32 @ctlz_decrement(i32 %n) {
+entry:
+  %tobool4 = icmp eq i32 %n, 0
+  br i1 %tobool4, label %while.end, label %while.body.preheader
+
+while.body.preheader:                             ; preds = %entry
+  br label %while.body
+
+while.body:                                       ; preds = %while.body.preheader, %while.body
+  %i.06 = phi i32 [ %inc, %while.body ], [ 32, %while.body.preheader ]
+  %n.addr.05 = phi i32 [ %shr, %while.body ], [ %n, %while.body.preheader ]
+  %shr = lshr i32 %n.addr.05, 1
+  %inc = add nsw i32 %i.06, -1
+  %tobool = icmp eq i32 %shr, 0
+  br i1 %tobool, label %while.end.loopexit, label %while.body
+
+while.end.loopexit:                               ; preds = %while.body
+  br label %while.end
+
+while.end:                                        ; preds = %while.end.loopexit, %entry
+  %i.0.lcssa = phi i32 [ 32, %entry ], [ %inc, %while.end.loopexit ]
+  ret i32 %i.0.lcssa
+}
+
+; Recognize CTLZ builtin pattern.
+; Here it will replace the loop -
+; assume builtin is always profitable.
+;
+; int ctlz_lshr_decrement(int n)
+; {
+;   int i = 31;
+;   while(n >>= 1) {
+;     i--;
+;   }
+;   return i;
+; }
+;
+; ALL:  entry
+; ALL:  %0 = lshr i32 %n, 1
+; ALL-NEXT:  %1 = call i32 @llvm.ctlz.i32(i32 %0, i1 false)
+; ALL-NEXT:  %2 = sub i32 32, %1
+; ALL-NEXT:  %3 = add i32 %2, 1
+; ALL-NEXT:  %4 = sub i32 31, %2
+; ALL:  %i.0.lcssa = phi i32 [ %4, %while.cond ]
+; ALL:  ret i32 %i.0.lcssa
+
+; Function Attrs: norecurse nounwind readnone uwtable
+define i32 @ctlz_lshr_decrement(i32 %n) {
+entry:
+  br label %while.cond
+
+while.cond:                                       ; preds = %while.cond, %entry
+  %n.addr.0 = phi i32 [ %n, %entry ], [ %shr, %while.cond ]
+  %i.0 = phi i32 [ 31, %entry ], [ %inc, %while.cond ]
+  %shr = lshr i32 %n.addr.0, 1
+  %tobool = icmp eq i32 %shr, 0
+  %inc = add nsw i32 %i.0, -1
+  br i1 %tobool, label %while.end, label %while.cond
+
+while.end:                                        ; preds = %while.cond
+  ret i32 %i.0
+}
diff --git a/llvm/test/Transforms/LoopIdiom/X86/cttz.ll b/llvm/test/Transforms/LoopIdiom/X86/cttz.ll
--- a/llvm/test/Transforms/LoopIdiom/X86/cttz.ll
+++ b/llvm/test/Transforms/LoopIdiom/X86/cttz.ll
@@ -80,3 +80,88 @@
   ret i32 %i.0
 }
 
+; Recognize CTTZ builtin pattern.
+; Here it will replace the loop -
+; assume builtin is always profitable.
+;
+; int ctlz_decrement(int n)
+; {
+;   int i = 32;
+;   while(n) {
+;     n <<= 1;
+;     i--;
+;   }
+;   return i;
+; }
+;
+; ALL:  entry
+; ALL:  %0 = call i32 @llvm.cttz.i32(i32 %n, i1 true)
+; ALL-NEXT:  %1 = sub i32 32, %0
+; ALL-NEXT:  %2 = sub i32 32, %1
+; ALL:  %inc.lcssa = phi i32 [ %2, %while.body ]
+; ALL:  %i.0.lcssa = phi i32 [ 32, %entry ], [ %inc.lcssa, %while.end.loopexit ]
+; ALL:  ret i32 %i.0.lcssa
+
+; Function Attrs: norecurse nounwind readnone uwtable
+define i32 @cttz_decrement(i32 %n) {
+entry:
+  %tobool4 = icmp eq i32 %n, 0
+  br i1 %tobool4, label %while.end, label %while.body.preheader
+
+while.body.preheader:                             ; preds = %entry
+  br label %while.body
+
+while.body:                                       ; preds = %while.body.preheader, %while.body
+  %i.06 = phi i32 [ %inc, %while.body ], [ 32, %while.body.preheader ]
+  %n.addr.05 = phi i32 [ %shl, %while.body ], [ %n, %while.body.preheader ]
+  %shl = shl i32 %n.addr.05, 1
+  %inc = add nsw i32 %i.06, -1
+  %tobool = icmp eq i32 %shl, 0
+  br i1 %tobool, label %while.end.loopexit, label %while.body
+
+while.end.loopexit:                               ; preds = %while.body
+  br label %while.end
+
+while.end:                                        ; preds = %while.end.loopexit, %entry
+  %i.0.lcssa = phi i32 [ 32, %entry ], [ %inc, %while.end.loopexit ]
+  ret i32 %i.0.lcssa
+}
+
+; Recognize CTTZ builtin pattern.
+; Here it will replace the loop -
+; assume builtin is always profitable.
+;
+; int cttz_shl_decrement(int n)
+; {
+;   int i = 31;
+;   while(n <<= 1) {
+;     i--;
+;   }
+;   return i;
+; }
+;
+; ALL:  entry
+; ALL:  %0 = shl i32 %n, 1
+; ALL-NEXT:  %1 = call i32 @llvm.cttz.i32(i32 %0, i1 false)
+; ALL-NEXT:  %2 = sub i32 32, %1
+; ALL-NEXT:  %3 = add i32 %2, 1
+; ALL-NEXT:  %4 = sub i32 31, %2
+; ALL:  %i.0.lcssa = phi i32 [ %4, %while.cond ]
+; ALL:  ret i32 %i.0.lcssa
+
+; Function Attrs: norecurse nounwind readnone uwtable
+define i32 @cttz_shl_decrement(i32 %n) {
+entry:
+  br label %while.cond
+
+while.cond:                                       ; preds = %while.cond, %entry
+  %n.addr.0 = phi i32 [ %n, %entry ], [ %shl, %while.cond ]
+  %i.0 = phi i32 [ 31, %entry ], [ %inc, %while.cond ]
+  %shl = shl i32 %n.addr.0, 1
+  %tobool = icmp eq i32 %shl, 0
+  %inc = add nsw i32 %i.0, -1
+  br i1 %tobool, label %while.end, label %while.cond
+
+while.end:                                        ; preds = %while.cond
+  ret i32 %i.0
+}