Index: lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
===================================================================
--- lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -1451,6 +1451,24 @@
     }
   }
 
+  // sin(a) / cos(a) -> tan(a)
+  if (AllowReassociate) {
+    if (IntrinsicInst *Sin = dyn_cast<IntrinsicInst>(Op0)) {
+      if (IntrinsicInst *Cos = dyn_cast<IntrinsicInst>(Op1)) {
+        if (Sin->getIntrinsicID() == Intrinsic::sin &&
+            Cos->getIntrinsicID() == Intrinsic::cos &&
+            Sin->getArgOperand(0) == Cos->getArgOperand(0)) {
+          Module *M = I.getModule();
+          Type *Ty = I.getType();
+          Value *Tan = M->getOrInsertFunction("tan", Ty, Ty);
+          Builder.setFastMathFlags(I.getFastMathFlags());
+          Value *TanCall = Builder.CreateCall(Tan, Cos->getArgOperand(0), "tan");
+          return replaceInstUsesWith(I, TanCall);
+        }
+      }
+    }
+  }
+
   Value *LHS;
   Value *RHS;
 
Index: test/Transforms/InstCombine/fdiv.ll
===================================================================
--- test/Transforms/InstCombine/fdiv.ll
+++ test/Transforms/InstCombine/fdiv.ll
@@ -67,3 +67,17 @@
   %div = fdiv fast float %x.fneg, %y.fneg
   ret float %div
 }
+
+; CHECK-LABEL @fdiv_sin_cos(
+; CHECK: call fast double @tan(double %a)
+define double @fdiv_sin_cos(double %a) {
+entry:
+  %0 = call fast double @llvm.sin.f64(double %a)
+  %1 = call fast double @llvm.cos.f64(double %a)
+  %div = fdiv fast double %0, %1
+  ret double %div
+}
+
+declare double @llvm.sin.f64(double) nounwind readnone speculatable
+declare double @llvm.cos.f64(double) nounwind readnone speculatable
+declare double @tan(double)