Index: lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
===================================================================
--- lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -555,6 +555,27 @@
   return (C0 && isFiniteNonZeroFp(C0)) || (C1 && isFiniteNonZeroFp(C1));
 }
 
+/// \brief Check whether the overloaded unary floating point function
+/// corresponding to \a Ty is available and return its LibName.
+static StringRef libFuncNameForUnaryFloatFn(const TargetLibraryInfo *TLI,
+                                            Type *Ty, LibFunc DoubleFn, 
+                                            LibFunc FloatFn, 
+                                            LibFunc LongDoubleFn) {
+  switch (Ty->getTypeID()) {
+    case Type::DoubleTyID:
+      if (TLI->has(DoubleFn))
+        return TLI->getName(DoubleFn);
+    case Type::FloatTyID:
+      if (TLI->has(FloatFn))
+        return TLI->getName(FloatFn);
+    default:
+      if (TLI->has(LongDoubleFn))
+        return TLI->getName(LongDoubleFn);
+  }
+  
+  return "";
+}
+
 /// foldFMulConst() is a helper routine of InstCombiner::visitFMul().
 /// The input \p FMulOrDiv is a FMul/FDiv with one and only one operand
 /// being a constant (i.e. isFMulOrFDivWithConstant(FMulOrDiv) == true).
@@ -1468,6 +1489,28 @@
     }
   }
 
+  // sin(a) / cos(a) -> tan(a)
+  if (AllowReassociate) {
+    Value *SinArg;
+    Value *CosArg;
+    if (match(Op0, m_Intrinsic<Intrinsic::sin>(m_Value(SinArg))) &&
+        match(Op1, m_Intrinsic<Intrinsic::cos>(m_Value(CosArg))) &&
+        SinArg == CosArg) {
+      BuilderTy::FastMathFlagGuard Guard(Builder);
+      Builder.setFastMathFlags(I.getFastMathFlags());
+      Type *Ty = I.getType();
+      StringRef FuncName =
+          libFuncNameForUnaryFloatFn(&TLI, Ty, LibFunc_tan,
+                                     LibFunc_tanf, LibFunc_tanl);
+      if (!FuncName.empty()) {
+        Module *M = I.getModule();
+        Value *Tan = M->getOrInsertFunction(FuncName, Ty, Ty);
+        Value *TanCall = Builder.CreateCall(Tan, SinArg);
+        return replaceInstUsesWith(I, TanCall);
+      }
+    }
+  }
+
   Value *LHS;
   Value *RHS;
 
Index: test/Transforms/InstCombine/fdiv.ll
===================================================================
--- test/Transforms/InstCombine/fdiv.ll
+++ test/Transforms/InstCombine/fdiv.ll
@@ -1,3 +1,4 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
 ; RUN: opt -S -instcombine < %s | FileCheck %s
 
 define float @test1(float %x) nounwind readnone ssp {
@@ -67,3 +68,63 @@
   %div = fdiv fast float %x.fneg, %y.fneg
   ret float %div
 }
+
+define double @fdiv_sin_cos(double %a) {
+; CHECK-LABEL: @fdiv_sin_cos(
+; CHECK-NEXT:    [[TMP1:%.*]] = call double @llvm.sin.f64(double [[A:%.*]])
+; CHECK-NEXT:    [[TMP2:%.*]] = call double @llvm.cos.f64(double [[A]])
+; CHECK-NEXT:    [[DIV:%.*]] = fdiv double [[TMP1]], [[TMP2]]
+; CHECK-NEXT:    ret double [[DIV]]
+;
+  %1 = call double @llvm.sin.f64(double %a)
+  %2 = call double @llvm.cos.f64(double %a)
+  %div = fdiv double %1, %2
+  ret double %div
+}
+
+define double @fdiv_sin_cos_fast(double %a) {
+; CHECK-LABEL: @fdiv_sin_cos_fast(
+; CHECK-NEXT:    [[TMP1:%.*]] = call fast double @tan(double [[A:%.*]])
+; CHECK-NEXT:    ret double [[TMP1]]
+;
+  %1 = call fast double @llvm.sin.f64(double %a)
+  %2 = call fast double @llvm.cos.f64(double %a)
+  %div = fdiv fast double %1, %2
+  ret double %div
+}
+
+define float @fdiv_sinf_cosf_fast(float %a) {
+; CHECK-LABEL: @fdiv_sinf_cosf_fast(
+; CHECK-NEXT:    [[TMP1:%.*]] = call fast float @tanf(float [[A:%.*]])
+; CHECK-NEXT:    ret float [[TMP1]]
+;
+  %1 = call fast float @llvm.sin.f32(float %a)
+  %2 = call fast float @llvm.cos.f32(float %a)
+  %div = fdiv fast float %1, %2
+  ret float %div
+}
+
+define fp128 @fdiv_sinfp128_cosfp128_fast(fp128 %a) {
+; CHECK-LABEL: @fdiv_sinfp128_cosfp128_fast(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[TMP0:%.*]] = call fast fp128 @tanl(fp128 [[A:%.*]])
+; CHECK-NEXT:    ret fp128 [[TMP0]]
+;
+entry:
+  %0 = call fast fp128 @llvm.sin.fp128(fp128 %a)
+  %1 = call fast fp128 @llvm.cos.fp128(fp128 %a)
+  %div = fdiv fast fp128 %0, %1
+  ret fp128 %div
+}
+
+declare double @llvm.sin.f64(double)
+declare float @llvm.sin.f32(float)
+declare fp128 @llvm.sin.fp128(fp128)
+
+declare double @llvm.cos.f64(double)
+declare float @llvm.cos.f32(float)
+declare fp128 @llvm.cos.fp128(fp128)
+
+declare double @tan(double)
+declare float @tanf(float)
+declare fp128 @tanl(fp128)