Index: include/llvm/Transforms/Utils/SimplifyLibCalls.h
===================================================================
--- include/llvm/Transforms/Utils/SimplifyLibCalls.h
+++ include/llvm/Transforms/Utils/SimplifyLibCalls.h
@@ -40,8 +40,7 @@
   ~LibCallSimplifier() {}
 
 public:
-  LibCallSimplifier(const DataLayout *TD, const TargetLibraryInfo *TLI,
-                    bool UnsafeFPShrink);
+  LibCallSimplifier(const DataLayout *TD, const TargetLibraryInfo *TLI);
 
   /// optimizeCall - Take the given call instruction and return a more
   /// optimal value to replace the instruction with or 0 if a more
Index: lib/Transforms/InstCombine/InstructionCombining.cpp
===================================================================
--- lib/Transforms/InstCombine/InstructionCombining.cpp
+++ lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -70,12 +70,6 @@
 STATISTIC(NumFactor   , "Number of factorizations");
 STATISTIC(NumReassoc  , "Number of reassociations");
 
-static cl::opt<bool>
-    EnableUnsafeFPShrink("enable-double-float-shrink", cl::Hidden,
-                         cl::init(false),
-                         cl::desc("Enable unsafe double to float "
-                                  "shrinking for math lib calls"));
-
 // Initialization Routines
 void llvm::initializeInstCombine(PassRegistry &Registry) {
   initializeInstCombinerPass(Registry);
@@ -2945,7 +2939,7 @@
   InstCombinerLibCallSimplifier(const DataLayout *DL,
                                 const TargetLibraryInfo *TLI,
                                 InstCombiner *IC)
-    : LibCallSimplifier(DL, TLI, EnableUnsafeFPShrink) {
+    : LibCallSimplifier(DL, TLI) {
     this->IC = IC;
   }
 
Index: lib/Transforms/Utils/SimplifyLibCalls.cpp
===================================================================
--- lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -40,6 +40,13 @@
     ColdErrorCalls("error-reporting-is-cold", cl::init(true), cl::Hidden,
                    cl::desc("Treat error-reporting calls as cold"));
 
+static cl::opt<bool>
+    EnableUnsafeFPShrink("enable-double-float-shrink", cl::Hidden,
+                         cl::init(false),
+                         cl::desc("Enable unsafe double to float "
+                                  "shrinking for math lib calls"));
+
+
 //===----------------------------------------------------------------------===//
 // Helper Functions
 //===----------------------------------------------------------------------===//
@@ -1989,6 +1996,20 @@
   IRBuilder<> Builder(CI);
   bool isCallingConvC = CI->getCallingConv() == llvm::CallingConv::C;
 
+  // Command-line parameter overrides function attribute.
+  if (EnableUnsafeFPShrink.getNumOccurrences() > 0)
+    UnsafeFPShrink = EnableUnsafeFPShrink;
+  else if (Callee->hasFnAttribute("unsafe-fp-math")) {
+    // FIXME: This is the same problem as described in optimizeSqrt().
+    // If calls gain access to IR-level FMF, then use that instead of a
+    // function attribute.
+
+    // Check for unsafe-fp-math = true.
+    Attribute Attr = Callee->getFnAttribute("unsafe-fp-math");
+    if (Attr.getValueAsString() == "true")
+      UnsafeFPShrink = true;
+  }
+
   // Next check for intrinsics.
   if (IntrinsicInst *II = dyn_cast<IntrinsicInst>(CI)) {
     if (!isCallingConvC)
@@ -2182,11 +2203,10 @@
 }
 
 LibCallSimplifier::LibCallSimplifier(const DataLayout *DL,
-                                     const TargetLibraryInfo *TLI,
-                                     bool UnsafeFPShrink) :
+                                     const TargetLibraryInfo *TLI) :
                                      DL(DL),
                                      TLI(TLI),
-                                     UnsafeFPShrink(UnsafeFPShrink) {
+                                     UnsafeFPShrink(false) {
 }
 
 void LibCallSimplifier::replaceAllUsesWith(Instruction *I, Value *With) const {
Index: test/Transforms/InstCombine/double-float-shrink-fast.ll
===================================================================
--- test/Transforms/InstCombine/double-float-shrink-fast.ll
+++ test/Transforms/InstCombine/double-float-shrink-fast.ll
@@ -0,0 +1,348 @@
+; RUN: opt < %s -instcombine -S | FileCheck %s
+
+; This repeats every test in double-float-shrink-1.ll except
+; we're checking for and against shrinkage when using the
+; unsafe-fp-math function attribute rather a command-line option.
+
+define float @acos_test(float %f)   {
+   %conv = fpext float %f to double
+   %call = call double @acos(double %conv)
+   %conv1 = fptrunc double %call to float
+   ret float %conv1
+; CHECK-LABEL: acos_test
+; CHECK: call float @acosf(float %f)
+}
+
+define double @acos_test2(float %f)   {
+   %conv = fpext float %f to double
+   %call = call double @acos(double %conv)
+   ret double %call
+; CHECK-LABEL: acos_test2
+; CHECK: call double @acos(double %conv)
+}
+
+define float @acosh_test(float %f)   {
+   %conv = fpext float %f to double
+   %call = call double @acosh(double %conv)
+   %conv1 = fptrunc double %call to float
+   ret float %conv1
+; CHECK-LABEL: acosh_test
+; CHECK: call float @acoshf(float %f)
+}
+
+define double @acosh_test2(float %f)   {
+   %conv = fpext float %f to double
+   %call = call double @acosh(double %conv)
+   ret double %call
+; CHECK-LABEL: acosh_test2
+; CHECK: call double @acosh(double %conv)
+}
+
+define float @asin_test(float %f)   {
+   %conv = fpext float %f to double
+   %call = call double @asin(double %conv)
+   %conv1 = fptrunc double %call to float
+   ret float %conv1
+; CHECK-LABEL: asin_test
+; CHECK: call float @asinf(float %f)
+}
+
+define double @asin_test2(float %f)   {
+   %conv = fpext float %f to double
+   %call = call double @asin(double %conv)
+   ret double %call
+; CHECK-LABEL: asin_test2
+; CHECK: call double @asin(double %conv)
+}
+
+define float @asinh_test(float %f)   {
+   %conv = fpext float %f to double
+   %call = call double @asinh(double %conv)
+   %conv1 = fptrunc double %call to float
+   ret float %conv1
+; CHECK-LABEL: asinh_test
+; CHECK: call float @asinhf(float %f)
+}
+
+define double @asinh_test2(float %f)   {
+   %conv = fpext float %f to double
+   %call = call double @asinh(double %conv)
+   ret double %call
+; CHECK-LABEL: asinh_test2
+; CHECK: call double @asinh(double %conv)
+}
+
+define float @atan_test(float %f)   {
+   %conv = fpext float %f to double
+   %call = call double @atan(double %conv)
+   %conv1 = fptrunc double %call to float
+   ret float %conv1
+; CHECK-LABEL: atan_test
+; CHECK: call float @atanf(float %f)
+}
+
+define double @atan_test2(float %f)   {
+   %conv = fpext float %f to double
+   %call = call double @atan(double %conv)
+   ret double %call
+; CHECK-LABEL: atan_test2
+; CHECK: call double @atan(double %conv)
+}
+define float @atanh_test(float %f)   {
+   %conv = fpext float %f to double
+   %call = call double @atanh(double %conv)
+   %conv1 = fptrunc double %call to float
+   ret float %conv1
+; CHECK-LABEL: atanh_test
+; CHECK: call float @atanhf(float %f)
+}
+
+define double @atanh_test2(float %f)   {
+    %conv = fpext float %f to double
+    %call = call double @atanh(double %conv)
+    ret double %call
+; CHECK-LABEL: atanh_test2
+; CHECK: call double @atanh(double %conv)
+}
+define float @cbrt_test(float %f)   {
+   %conv = fpext float %f to double
+   %call = call double @cbrt(double %conv)
+   %conv1 = fptrunc double %call to float
+   ret float %conv1
+; CHECK-LABEL: cbrt_test
+; CHECK: call float @cbrtf(float %f)
+}
+
+define double @cbrt_test2(float %f)   {
+   %conv = fpext float %f to double
+   %call = call double @cbrt(double %conv)
+   ret double %call
+; CHECK-LABEL: cbrt_test2
+; CHECK: call double @cbrt(double %conv)
+}
+define float @exp_test(float %f)   {
+   %conv = fpext float %f to double
+   %call = call double @exp(double %conv)
+   %conv1 = fptrunc double %call to float
+   ret float %conv1
+; CHECK-LABEL: exp_test
+; CHECK: call float @expf(float %f)
+}
+
+define double @exp_test2(float %f)   {
+   %conv = fpext float %f to double
+   %call = call double @exp(double %conv)
+   ret double %call
+; CHECK-LABEL: exp_test2
+; CHECK: call double @exp(double %conv)
+}
+define float @expm1_test(float %f)   {
+   %conv = fpext float %f to double
+   %call = call double @expm1(double %conv)
+   %conv1 = fptrunc double %call to float
+   ret float %conv1
+; CHECK-LABEL: expm1_test
+; CHECK: call float @expm1f(float %f)
+}
+
+define double @expm1_test2(float %f)   {
+   %conv = fpext float %f to double
+   %call = call double @expm1(double %conv)
+   ret double %call
+; CHECK-LABEL: expm1_test2
+; CHECK: call double @expm1(double %conv)
+}
+define float @exp10_test(float %f)   {
+   %conv = fpext float %f to double
+   %call = call double @exp10(double %conv)
+   %conv1 = fptrunc double %call to float
+   ret float %conv1
+; CHECK-LABEL: exp10_test
+; CHECK: call double @exp10(double %conv)
+}
+
+define double @exp10_test2(float %f)   {
+   %conv = fpext float %f to double
+   %call = call double @exp10(double %conv)
+   ret double %call
+; CHECK-LABEL: exp10_test2
+; CHECK: call double @exp10(double %conv)
+}
+define float @log_test(float %f)   {
+   %conv = fpext float %f to double
+   %call = call double @log(double %conv)
+   %conv1 = fptrunc double %call to float
+   ret float %conv1
+; CHECK-LABEL: log_test
+; CHECK: call float @logf(float %f)
+}
+
+define double @log_test2(float %f)   {
+   %conv = fpext float %f to double
+   %call = call double @log(double %conv)
+   ret double %call
+; CHECK-LABEL: log_test2
+; CHECK: call double @log(double %conv)
+}
+define float @log10_test(float %f)   {
+   %conv = fpext float %f to double
+   %call = call double @log10(double %conv)
+   %conv1 = fptrunc double %call to float
+   ret float %conv1
+; CHECK-LABEL: log10_test
+; CHECK: call float @log10f(float %f)
+}
+
+define double @log10_test2(float %f) {
+   %conv = fpext float %f to double
+   %call = call double @log10(double %conv)
+   ret double %call
+; CHECK-LABEL: log10_test2
+; CHECK: call double @log10(double %conv)
+}
+define float @log1p_test(float %f)   {
+   %conv = fpext float %f to double
+   %call = call double @log1p(double %conv)
+   %conv1 = fptrunc double %call to float
+   ret float %conv1
+; CHECK-LABEL: log1p_test
+; CHECK: call float @log1pf(float %f)
+}
+
+define double @log1p_test2(float %f)   {
+   %conv = fpext float %f to double
+   %call = call double @log1p(double %conv)
+   ret double %call
+; CHECK-LABEL: log1p_test2
+; CHECK: call double @log1p(double %conv)
+}
+define float @log2_test(float %f)   {
+   %conv = fpext float %f to double
+   %call = call double @log2(double %conv)
+   %conv1 = fptrunc double %call to float
+   ret float %conv1
+; CHECK-LABEL: log2_test
+; CHECK: call float @log2f(float %f)
+}
+
+define double @log2_test2(float %f)   {
+   %conv = fpext float %f to double
+   %call = call double @log2(double %conv)
+   ret double %call
+; CHECK-LABEL: log2_test2
+; CHECK: call double @log2(double %conv)
+}
+define float @logb_test(float %f)   {
+   %conv = fpext float %f to double
+   %call = call double @logb(double %conv)
+   %conv1 = fptrunc double %call to float
+   ret float %conv1
+; CHECK-LABEL: logb_test
+; CHECK: call float @logbf(float %f)
+}
+
+define double @logb_test2(float %f)   {
+   %conv = fpext float %f to double
+   %call = call double @logb(double %conv)
+   ret double %call
+; CHECK-LABEL: logb_test2
+; CHECK: call double @logb(double %conv)
+}
+define float @sin_test(float %f)   {
+   %conv = fpext float %f to double
+   %call = call double @sin(double %conv)
+   %conv1 = fptrunc double %call to float
+   ret float %conv1
+; CHECK-LABEL: sin_test
+; CHECK: call float @sinf(float %f)
+}
+
+define double @sin_test2(float %f) {
+   %conv = fpext float %f to double
+   %call = call double @sin(double %conv)
+   ret double %call
+; CHECK-LABEL: sin_test2
+; CHECK: call double @sin(double %conv)
+}
+
+define float @sqrt_test(float %f) {
+   %conv = fpext float %f to double
+   %call = call double @sqrt(double %conv)
+   %conv1 = fptrunc double %call to float
+   ret float %conv1
+; CHECK-LABEL: sqrt_test
+; CHECK: call float @sqrtf(float %f)
+}
+
+define float @sqrt_int_test(float %f) {
+   %conv = fpext float %f to double
+   %call = call double @llvm.sqrt.f64(double %conv)
+   %conv1 = fptrunc double %call to float
+   ret float %conv1
+; CHECK-LABEL: sqrt_int_test
+; CHECK: call float @llvm.sqrt.f32(float %f)
+}
+
+define double @sqrt_test2(float %f) {
+   %conv = fpext float %f to double
+   %call = call double @sqrt(double %conv)
+   ret double %call
+; CHECK-LABEL: sqrt_test2
+; CHECK: call double @sqrt(double %conv)
+}
+define float @tan_test(float %f) {
+   %conv = fpext float %f to double
+   %call = call double @tan(double %conv)
+   %conv1 = fptrunc double %call to float
+   ret float %conv1
+; CHECK-LABEL: tan_test
+; CHECK: call float @tanf(float %f)
+}
+
+define double @tan_test2(float %f) {
+   %conv = fpext float %f to double
+   %call = call double @tan(double %conv)
+   ret double %call
+; CHECK-LABEL: tan_test2
+; CHECK: call double @tan(double %conv)
+}
+define float @tanh_test(float %f) {
+   %conv = fpext float %f to double
+   %call = call double @tanh(double %conv)
+   %conv1 = fptrunc double %call to float
+   ret float %conv1
+; CHECK-LABEL: tanh_test
+; CHECK: call float @tanhf(float %f)
+}
+
+define double @tanh_test2(float %f) {
+   %conv = fpext float %f to double
+   %call = call double @tanh(double %conv)
+   ret double %call
+; CHECK-LABEL: tanh_test2
+; CHECK: call double @tanh(double %conv)
+}
+
+declare double @tanh(double) #1
+declare double @tan(double) #1
+declare double @sqrt(double) #1
+declare double @sin(double) #1
+declare double @log2(double) #1
+declare double @log1p(double) #1
+declare double @log10(double) #1
+declare double @log(double) #1
+declare double @logb(double) #1
+declare double @exp10(double) #1
+declare double @expm1(double) #1
+declare double @exp(double) #1
+declare double @cbrt(double) #1
+declare double @atanh(double) #1
+declare double @atan(double) #1
+declare double @acos(double) #1
+declare double @acosh(double) #1
+declare double @asin(double) #1
+declare double @asinh(double) #1
+
+declare double @llvm.sqrt.f64(double) #1
+attributes #1 = { "unsafe-fp-math"="true" }
+