diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index 0038633cd6e..4a6f409a16c 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -5627,7 +5627,8 @@ void SelectionDAGBuilder::visitCall(const CallInst &I) {
                  (LibInfo->has(LibFunc::log2l) && Name == "log2l")) {
         if (I.getNumArgOperands() == 1 && // Basic sanity checks.
             I.getArgOperand(0)->getType()->isFloatingPointTy() &&
-            I.getType() == I.getArgOperand(0)->getType()) {
+            I.getType() == I.getArgOperand(0)->getType() &&
+            I.onlyReadsMemory()) {
           SDValue Tmp = getValue(I.getArgOperand(0));
           setValue(&I, DAG.getNode(ISD::FLOG2, getCurDebugLoc(),
                                    Tmp.getValueType(), Tmp));
@@ -5638,7 +5639,8 @@ void SelectionDAGBuilder::visitCall(const CallInst &I) {
                  (LibInfo->has(LibFunc::exp2l) && Name == "exp2l")) {
         if (I.getNumArgOperands() == 1 && // Basic sanity checks.
             I.getArgOperand(0)->getType()->isFloatingPointTy() &&
-            I.getType() == I.getArgOperand(0)->getType()) {
+            I.getType() == I.getArgOperand(0)->getType() &&
+            I.onlyReadsMemory()) {
           SDValue Tmp = getValue(I.getArgOperand(0));
           setValue(&I, DAG.getNode(ISD::FEXP2, getCurDebugLoc(),
                                    Tmp.getValueType(), Tmp));
diff --git a/test/CodeGen/ARM/log2_not_readnone.ll b/test/CodeGen/ARM/log2_not_readnone.ll
new file mode 100644
index 00000000000..4d567eda65d
--- /dev/null
+++ b/test/CodeGen/ARM/log2_not_readnone.ll
@@ -0,0 +1,15 @@
+; RUN: llc -march arm %s -o - | FileCheck %s
+
+; Log2 and exp2 are string-matched to intrinsics. If they are not declared
+; readnone, they can't be changed to intrinsics (because they can change errno).
+
+declare double @log2(double)
+declare double @exp2(double)
+
+define void @f() {
+       ; CHECK: bl log2
+       %1 = call double @log2(double 0.000000e+00)
+       ; CHECK: bl exp2
+       %2 = call double @exp2(double 0.000000e+00)
+       ret void
+}
diff --git a/test/CodeGen/X86/log2_not_readnone.ll b/test/CodeGen/X86/log2_not_readnone.ll
new file mode 100644
index 00000000000..a971b0b442f
--- /dev/null
+++ b/test/CodeGen/X86/log2_not_readnone.ll
@@ -0,0 +1,15 @@
+; RUN: llc -march x86 %s -o - | FileCheck %s
+
+; Log2 and exp2 are string-matched to intrinsics. If they are not declared
+; readnone, they can't be changed to intrinsics (because they can change errno).
+
+declare double @log2(double)
+declare double @exp2(double)
+
+define void @f() {
+       ; CHECK: calll log2
+       %1 = call double @log2(double 0.000000e+00)
+       ; CHECK: calll exp2
+       %2 = call double @exp2(double 0.000000e+00)
+       ret void
+}