diff --git a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 0d5cabaaf27..107f5a12693 100644
--- a/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -1155,6 +1155,13 @@ void DAGCombiner::Run(CombineLevel AtLevel) {
   LegalOperations = Level >= AfterLegalizeVectorOps;
   LegalTypes = Level >= AfterLegalizeTypes;
 
+  // Early exit if this basic block is in an optnone function.
+  AttributeSet FnAttrs =
+    DAG.getMachineFunction().getFunction()->getAttributes();
+  if (FnAttrs.hasAttribute(AttributeSet::FunctionIndex,
+                           Attribute::OptimizeNone))
+    return;
+
   // Add all the dag nodes to the worklist.
   for (SelectionDAG::allnodes_iterator I = DAG.allnodes_begin(),
        E = DAG.allnodes_end(); I != E; ++I)
diff --git a/test/CodeGen/X86/fastmath-optnone.ll b/test/CodeGen/X86/fastmath-optnone.ll
new file mode 100644
index 00000000000..0caadff8916
--- /dev/null
+++ b/test/CodeGen/X86/fastmath-optnone.ll
@@ -0,0 +1,35 @@
+; RUN: llc < %s -mcpu=corei7 -march=x86-64 -mattr=+sse2 | FileCheck %s
+; Verify that floating-point operations inside 'optnone' functions
+; are not optimized even if unsafe-fp-math is set.
+
+define float @foo(float %x) #0 {
+entry:
+  %add = fadd fast float %x, %x
+  %add1 = fadd fast float %add, %x
+  ret float %add1
+}
+
+; CHECK-LABEL: @foo
+; CHECK-NOT: add
+; CHECK: mul
+; CHECK-NOT: add
+; CHECK: ret
+
+define float @fooWithOptnone(float %x) #1 {
+entry:
+  %add = fadd fast float %x, %x
+  %add1 = fadd fast float %add, %x
+  ret float %add1
+}
+
+; CHECK-LABEL: @fooWithOptnone
+; CHECK-NOT: mul
+; CHECK: add
+; CHECK-NOT: mul
+; CHECK: add
+; CHECK-NOT: mul
+; CHECK: ret
+
+
+attributes #0 = { "unsafe-fp-math"="true" }
+attributes #1 = { noinline optnone "unsafe-fp-math"="true" }
diff --git a/test/Transforms/FunctionAttrs/optnone-simple.ll b/test/Transforms/FunctionAttrs/optnone-simple.ll
new file mode 100644
index 00000000000..9d0f8e3710a
--- /dev/null
+++ b/test/Transforms/FunctionAttrs/optnone-simple.ll
@@ -0,0 +1,135 @@
+; RUN: opt -O3 -S < %s | FileCheck %s
+; Show 'optnone' suppresses optimizations.
+
+; Two attribute groups that differ only by 'optnone'.
+; 'optnone' requires 'noinline' so #0 is 'noinline' by itself,
+; even though it would otherwise be irrelevant to this example.
+attributes #0 = { noinline }
+attributes #1 = { noinline optnone }
+
+; int iadd(int a, int b){ return a + b; }
+
+define i32 @iadd_optimize(i32 %a, i32 %b) #0 {
+entry:
+  %a.addr = alloca i32, align 4
+  %b.addr = alloca i32, align 4
+  store i32 %a, i32* %a.addr, align 4
+  store i32 %b, i32* %b.addr, align 4
+  %0 = load i32* %a.addr, align 4
+  %1 = load i32* %b.addr, align 4
+  %add = add nsw i32 %0, %1
+  ret i32 %add
+}
+
+; CHECK-LABEL: @iadd_optimize
+; CHECK-NOT: alloca
+; CHECK-NOT: store
+; CHECK-NOT: load
+; CHECK: ret
+
+define i32 @iadd_optnone(i32 %a, i32 %b) #1 {
+entry:
+  %a.addr = alloca i32, align 4
+  %b.addr = alloca i32, align 4
+  store i32 %a, i32* %a.addr, align 4
+  store i32 %b, i32* %b.addr, align 4
+  %0 = load i32* %a.addr, align 4
+  %1 = load i32* %b.addr, align 4
+  %add = add nsw i32 %0, %1
+  ret i32 %add
+}
+
+; CHECK-LABEL: @iadd_optnone
+; CHECK: alloca i32
+; CHECK: alloca i32
+; CHECK: store i32
+; CHECK: store i32
+; CHECK: load i32
+; CHECK: load i32
+; CHECK: add nsw i32
+; CHECK: ret i32
+
+; float fsub(float a, float b){ return a - b; }
+
+define float @fsub_optimize(float %a, float %b) #0 {
+entry:
+  %a.addr = alloca float, align 4
+  %b.addr = alloca float, align 4
+  store float %a, float* %a.addr, align 4
+  store float %b, float* %b.addr, align 4
+  %0 = load float* %a.addr, align 4
+  %1 = load float* %b.addr, align 4
+  %sub = fsub float %0, %1
+  ret float %sub
+}
+
+; CHECK-LABEL: @fsub_optimize
+; CHECK-NOT: alloca
+; CHECK-NOT: store
+; CHECK-NOT: load
+; CHECK: ret
+
+define float @fsub_optnone(float %a, float %b) #1 {
+entry:
+  %a.addr = alloca float, align 4
+  %b.addr = alloca float, align 4
+  store float %a, float* %a.addr, align 4
+  store float %b, float* %b.addr, align 4
+  %0 = load float* %a.addr, align 4
+  %1 = load float* %b.addr, align 4
+  %sub = fsub float %0, %1
+  ret float %sub
+}
+
+; CHECK-LABEL: @fsub_optnone
+; CHECK: alloca float
+; CHECK: alloca float
+; CHECK: store float
+; CHECK: store float
+; CHECK: load float
+; CHECK: load float
+; CHECK: fsub float
+; CHECK: ret float
+
+; typedef float __attribute__((ext_vector_type(4))) float4;
+; float4 vmul(float4 a, float4 b){ return a * b; }
+
+define <4 x float> @vmul_optimize(<4 x float> %a, <4 x float> %b) #0 {
+entry:
+  %a.addr = alloca <4 x float>, align 16
+  %b.addr = alloca <4 x float>, align 16
+  store <4 x float> %a, <4 x float>* %a.addr, align 16
+  store <4 x float> %b, <4 x float>* %b.addr, align 16
+  %0 = load <4 x float>* %a.addr, align 16
+  %1 = load <4 x float>* %b.addr, align 16
+  %mul = fmul <4 x float> %0, %1
+  ret <4 x float> %mul
+}
+
+; CHECK-LABEL: @vmul_optimize
+; CHECK-NOT: alloca
+; CHECK-NOT: store
+; CHECK-NOT: load
+; CHECK: ret
+
+define <4 x float> @vmul_optnone(<4 x float> %a, <4 x float> %b) #1 {
+entry:
+  %a.addr = alloca <4 x float>, align 16
+  %b.addr = alloca <4 x float>, align 16
+  store <4 x float> %a, <4 x float>* %a.addr, align 16
+  store <4 x float> %b, <4 x float>* %b.addr, align 16
+  %0 = load <4 x float>* %a.addr, align 16
+  %1 = load <4 x float>* %b.addr, align 16
+  %mul = fmul <4 x float> %0, %1
+  ret <4 x float> %mul
+}
+
+; CHECK-LABEL: @vmul_optnone
+; CHECK: alloca <4 x float>
+; CHECK: alloca <4 x float>
+; CHECK: store <4 x float>
+; CHECK: store <4 x float>
+; CHECK: load <4 x float>
+; CHECK: load <4 x float>
+; CHECK: fmul <4 x float>
+; CHECK: ret