diff --git a/include/llvm/Instruction.h b/include/llvm/Instruction.h
index 22c8289c73a..2c1d41c705b 100644
--- a/include/llvm/Instruction.h
+++ b/include/llvm/Instruction.h
@@ -253,7 +253,7 @@ public:
   ///
   /// In LLVM, the Add, Mul, And, Or, and Xor operators are associative.
   ///
-  bool isAssociative() const { return isAssociative(getOpcode()); }
+  bool isAssociative() const;
   static bool isAssociative(unsigned op);
 
   /// isCommutative - Return true if the instruction is commutative:
diff --git a/lib/VMCore/Instruction.cpp b/lib/VMCore/Instruction.cpp
index 4208144cb5b..d93c1d7a22c 100644
--- a/lib/VMCore/Instruction.cpp
+++ b/lib/VMCore/Instruction.cpp
@@ -468,6 +468,20 @@ bool Instruction::isAssociative(unsigned Opcode) {
          Opcode == Add || Opcode == Mul;
 }
 
+bool Instruction::isAssociative() const {
+  unsigned Opcode = getOpcode();
+  if (isAssociative(Opcode))
+    return true;
+
+  switch (Opcode) {
+  case FMul:
+  case FAdd:
+    return cast<FPMathOperator>(this)->hasUnsafeAlgebra();
+  default:
+    return false;
+  }
+}
+
 /// isCommutative - Return true if the instruction is commutative:
 ///
 ///   Commutative operators satisfy: (x op y) === (y op x)
diff --git a/test/Transforms/InstCombine/fast-math.ll b/test/Transforms/InstCombine/fast-math.ll
new file mode 100644
index 00000000000..42241409ff8
--- /dev/null
+++ b/test/Transforms/InstCombine/fast-math.ll
@@ -0,0 +1,32 @@
+; RUN: opt < %s -instcombine -S | FileCheck %s
+
+; testing-case "float fold(float a) { return 1.2f * a * 2.3f; }"
+; 1.2f and 2.3f is supposed to be fold.
+define float @fold(float %a) {
+fold:
+  %mul = fmul fast float %a, 0x3FF3333340000000
+  %mul1 = fmul fast float %mul, 0x4002666660000000
+  ret float %mul1
+; CHECK: fold
+; CHECK: fmul float %a, 0x4006147AE0000000
+}
+
+; Same testing-case as the one used in fold() except that the operators have
+; fixed FP mode.
+define float @notfold(float %a) {
+notfold:
+; CHECK: notfold
+; CHECK: %mul = fmul fast float %a, 0x3FF3333340000000
+  %mul = fmul fast float %a, 0x3FF3333340000000
+  %mul1 = fmul float %mul, 0x4002666660000000
+  ret float %mul1
+}
+
+define float @fold2(float %a) {
+notfold2:
+; CHECK: fold2
+; CHECK: fmul float %a, 0x4006147AE0000000
+  %mul = fmul float %a, 0x3FF3333340000000
+  %mul1 = fmul fast float %mul, 0x4002666660000000
+  ret float %mul1
+}