diff --git a/js/src/assembler/assembler/X86Assembler.h b/js/src/assembler/assembler/X86Assembler.h
index 05a7fa4c9817..751b013008e0 100644
--- a/js/src/assembler/assembler/X86Assembler.h
+++ b/js/src/assembler/assembler/X86Assembler.h
@@ -2643,6 +2643,14 @@ public:
         m_formatter.twoByteRipOp(OP2_MOVSD_VsdWsd, (RegisterID)dst, 0);
         return JmpSrc(m_formatter.size());
     }
+    JmpSrc movss_ripr(XMMRegisterID dst)
+    {
+        spew("movss      \?(%%rip), %s",
+             nameFPReg(dst));
+        m_formatter.prefix(PRE_SSE_F3);
+        m_formatter.twoByteRipOp(OP2_MOVSD_VsdWsd, (RegisterID)dst, 0);
+        return JmpSrc(m_formatter.size());
+    }
     JmpSrc movsd_rrip(XMMRegisterID src)
     {
         spew("movsd      %s, \?(%%rip)",
diff --git a/js/src/jit/x64/MacroAssembler-x64.cpp b/js/src/jit/x64/MacroAssembler-x64.cpp
index 09bd3e232446..a4f914dbac72 100644
--- a/js/src/jit/x64/MacroAssembler-x64.cpp
+++ b/js/src/jit/x64/MacroAssembler-x64.cpp
@@ -48,12 +48,46 @@ MacroAssemblerX64::loadConstantDouble(double d, const FloatRegister &dest)
     masm.setNextJump(j, prev);
 }
 
+void
+MacroAssemblerX64::loadConstantFloat32(float f, const FloatRegister &dest)
+{
+    // In particular, use hardware instructions if loading 0
+    uint32_t u = mozilla::BitwiseCast<uint32_t>(f);
+    if (u == 0) {
+        xorps(dest, dest);
+        return;
+    }
+
+    if (!floatMap_.initialized()) {
+        enoughMemory_ &= floatMap_.init();
+        if (!enoughMemory_)
+            return;
+    }
+    size_t floatIndex;
+    if (FloatMap::AddPtr p = floatMap_.lookupForAdd(f)) {
+        floatIndex = p->value;
+    } else {
+        floatIndex = floats_.length();
+        enoughMemory_ &= floats_.append(Float(f));
+        enoughMemory_ &= floatMap_.add(p, f, floatIndex);
+        if (!enoughMemory_)
+            return;
+    }
+    Float &flt = floats_[floatIndex];
+    JS_ASSERT(!flt.uses.bound());
+
+    // See comment in loadConstantDouble
+    JmpSrc j = masm.movss_ripr(dest.code());
+    JmpSrc prev = JmpSrc(flt.uses.use(j.offset()));
+    masm.setNextJump(j, prev);
+}
+
 void
 MacroAssemblerX64::finish()
 {
     JS_STATIC_ASSERT(CodeAlignment >= sizeof(double));
 
-    if (!doubles_.empty())
+    if (!doubles_.empty() || !floats_.empty())
         masm.align(sizeof(double));
 
     for (size_t i = 0; i < doubles_.length(); i++) {
@@ -62,6 +96,13 @@ MacroAssemblerX64::finish()
         masm.doubleConstant(dbl.value);
     }
 
+    // No need to align on sizeof(float) as we are aligned on sizeof(double);
+    for (size_t i = 0; i < floats_.length(); i++) {
+        Float &flt = floats_[i];
+        bind(&flt.uses);
+        masm.floatConstant(flt.value);
+    }
+
     MacroAssemblerX86Shared::finish();
 }
 
diff --git a/js/src/jit/x64/MacroAssembler-x64.h b/js/src/jit/x64/MacroAssembler-x64.h
index 7e9bf376d806..f21bbf15f6b9 100644
--- a/js/src/jit/x64/MacroAssembler-x64.h
+++ b/js/src/jit/x64/MacroAssembler-x64.h
@@ -57,6 +57,16 @@ class MacroAssemblerX64 : public MacroAssemblerX86Shared
     typedef HashMap<double, size_t, DefaultHasher<double>, SystemAllocPolicy> DoubleMap;
     DoubleMap doubleMap_;
 
+    struct Float {
+        float value;
+        NonAssertingLabel uses;
+        Float(float value) : value(value) {}
+    };
+    Vector<Float, 0, SystemAllocPolicy> floats_;
+
+    typedef HashMap<float, size_t, DefaultHasher<float>, SystemAllocPolicy> FloatMap;
+    FloatMap floatMap_;
+
     void setupABICall(uint32_t arg);
 
   protected:
@@ -1010,15 +1020,7 @@ class MacroAssemblerX64 : public MacroAssemblerX86Shared
     }
 
     void loadConstantDouble(double d, const FloatRegister &dest);
-    void loadConstantFloat32(float f, const FloatRegister &dest) {
-        union FloatPun {
-            uint32_t u;
-            float f;
-        } pun;
-        pun.f = f;
-        mov(ImmWord(pun.u), ScratchReg);
-        movq(ScratchReg, dest);
-    }
+    void loadConstantFloat32(float f, const FloatRegister &dest);
 
     void branchTruncateDouble(const FloatRegister &src, const Register &dest, Label *fail) {
         const uint64_t IndefiniteIntegerValue = 0x8000000000000000;