Index: llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp
===================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -1324,12 +1324,20 @@
   assert((II.getIntrinsicID() == Intrinsic::cttz ||
           II.getIntrinsicID() == Intrinsic::ctlz) &&
          "Expected cttz or ctlz intrinsic");
+  bool IsTZ = II.getIntrinsicID() == Intrinsic::cttz;
   Value *Op0 = II.getArgOperand(0);
+  Value *X;
+  // ctlz(bitreverse(x)) -> cttz(x)
+  // cttz(bitreverse(x)) -> ctlz(x)
+  if (match(Op0, m_BitReverse(m_Value(X)))) {
+    Intrinsic::ID ID = IsTZ ? Intrinsic::ctlz : Intrinsic::cttz;
+    Function *F = Intrinsic::getDeclaration(II.getModule(), ID, II.getType());
+    return CallInst::Create(F, {X, II.getArgOperand(1)});
+  }
 
   KnownBits Known = IC.computeKnownBits(Op0, 0, &II);
 
   // Create a mask for bits above (ctlz) or below (cttz) the first known one.
-  bool IsTZ = II.getIntrinsicID() == Intrinsic::cttz;
   unsigned PossibleZeros = IsTZ ? Known.countMaxTrailingZeros()
                                 : Known.countMaxLeadingZeros();
   unsigned DefiniteZeros = IsTZ ? Known.countMinTrailingZeros()
Index: llvm/trunk/test/Transforms/InstCombine/ctlz-cttz-bitreverse.ll
===================================================================
--- llvm/trunk/test/Transforms/InstCombine/ctlz-cttz-bitreverse.ll
+++ llvm/trunk/test/Transforms/InstCombine/ctlz-cttz-bitreverse.ll
@@ -3,9 +3,8 @@
 
 define i32 @ctlz_true_bitreverse(i32 %x) {
 ; CHECK-LABEL: @ctlz_true_bitreverse(
-; CHECK-NEXT:    [[A:%.*]] = tail call i32 @llvm.bitreverse.i32(i32 [[X:%.*]])
-; CHECK-NEXT:    [[B:%.*]] = tail call i32 @llvm.ctlz.i32(i32 [[A]], i1 true), !range !0
-; CHECK-NEXT:    ret i32 [[B]]
+; CHECK-NEXT:    [[TMP1:%.*]] = call i32 @llvm.cttz.i32(i32 [[X:%.*]], i1 true), !range !0
+; CHECK-NEXT:    ret i32 [[TMP1]]
 ;
   %a = tail call i32 @llvm.bitreverse.i32(i32 %x)
   %b = tail call i32 @llvm.ctlz.i32(i32 %a, i1 true)
@@ -14,9 +13,8 @@
 
 define <2 x i64> @ctlz_true_bitreverse_vec(<2 x i64> %x) {
 ; CHECK-LABEL: @ctlz_true_bitreverse_vec(
-; CHECK-NEXT:    [[A:%.*]] = tail call <2 x i64> @llvm.bitreverse.v2i64(<2 x i64> [[X:%.*]])
-; CHECK-NEXT:    [[B:%.*]] = tail call <2 x i64> @llvm.ctlz.v2i64(<2 x i64> [[A]], i1 true)
-; CHECK-NEXT:    ret <2 x i64> [[B]]
+; CHECK-NEXT:    [[TMP1:%.*]] = call <2 x i64> @llvm.cttz.v2i64(<2 x i64> [[X:%.*]], i1 true)
+; CHECK-NEXT:    ret <2 x i64> [[TMP1]]
 ;
   %a = tail call <2 x i64> @llvm.bitreverse.v2i64(<2 x i64> %x)
   %b = tail call <2 x i64> @llvm.ctlz.v2i64(<2 x i64> %a, i1 true)
@@ -25,9 +23,8 @@
 
 define i32 @ctlz_false_bitreverse(i32 %x) {
 ; CHECK-LABEL: @ctlz_false_bitreverse(
-; CHECK-NEXT:    [[A:%.*]] = tail call i32 @llvm.bitreverse.i32(i32 [[X:%.*]])
-; CHECK-NEXT:    [[B:%.*]] = tail call i32 @llvm.ctlz.i32(i32 [[A]], i1 false), !range !0
-; CHECK-NEXT:    ret i32 [[B]]
+; CHECK-NEXT:    [[TMP1:%.*]] = call i32 @llvm.cttz.i32(i32 [[X:%.*]], i1 false), !range !0
+; CHECK-NEXT:    ret i32 [[TMP1]]
 ;
   %a = tail call i32 @llvm.bitreverse.i32(i32 %x)
   %b = tail call i32 @llvm.ctlz.i32(i32 %a, i1 false)
@@ -36,9 +33,8 @@
 
 define i32 @cttz_true_bitreverse(i32 %x) {
 ; CHECK-LABEL: @cttz_true_bitreverse(
-; CHECK-NEXT:    [[A:%.*]] = tail call i32 @llvm.bitreverse.i32(i32 [[X:%.*]])
-; CHECK-NEXT:    [[B:%.*]] = tail call i32 @llvm.cttz.i32(i32 [[A]], i1 true), !range !0
-; CHECK-NEXT:    ret i32 [[B]]
+; CHECK-NEXT:    [[TMP1:%.*]] = call i32 @llvm.ctlz.i32(i32 [[X:%.*]], i1 true), !range !0
+; CHECK-NEXT:    ret i32 [[TMP1]]
 ;
   %a = tail call i32 @llvm.bitreverse.i32(i32 %x)
   %b = tail call i32 @llvm.cttz.i32(i32 %a, i1 true)
@@ -47,9 +43,8 @@
 
 define <2 x i64> @cttz_true_bitreverse_vec(<2 x i64> %x) {
 ; CHECK-LABEL: @cttz_true_bitreverse_vec(
-; CHECK-NEXT:    [[A:%.*]] = tail call <2 x i64> @llvm.bitreverse.v2i64(<2 x i64> [[X:%.*]])
-; CHECK-NEXT:    [[B:%.*]] = tail call <2 x i64> @llvm.cttz.v2i64(<2 x i64> [[A]], i1 true)
-; CHECK-NEXT:    ret <2 x i64> [[B]]
+; CHECK-NEXT:    [[TMP1:%.*]] = call <2 x i64> @llvm.ctlz.v2i64(<2 x i64> [[X:%.*]], i1 true)
+; CHECK-NEXT:    ret <2 x i64> [[TMP1]]
 ;
   %a = tail call <2 x i64> @llvm.bitreverse.v2i64(<2 x i64> %x)
   %b = tail call <2 x i64> @llvm.cttz.v2i64(<2 x i64> %a, i1 true)
@@ -58,9 +53,8 @@
 
 define i32 @cttz_false_bitreverse(i32 %x) {
 ; CHECK-LABEL: @cttz_false_bitreverse(
-; CHECK-NEXT:    [[A:%.*]] = tail call i32 @llvm.bitreverse.i32(i32 [[X:%.*]])
-; CHECK-NEXT:    [[B:%.*]] = tail call i32 @llvm.cttz.i32(i32 [[A]], i1 false), !range !0
-; CHECK-NEXT:    ret i32 [[B]]
+; CHECK-NEXT:    [[TMP1:%.*]] = call i32 @llvm.ctlz.i32(i32 [[X:%.*]], i1 false), !range !0
+; CHECK-NEXT:    ret i32 [[TMP1]]
 ;
   %a = tail call i32 @llvm.bitreverse.i32(i32 %x)
   %b = tail call i32 @llvm.cttz.i32(i32 %a, i1 false)