Index: lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
===================================================================
--- lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -1748,7 +1748,7 @@
   // E.g. (icmp sgt x, n) | (icmp slt x, 0) --> icmp ugt x, n
   if (Value *V = simplifyRangeCheck(RHS, LHS, /*Inverted=*/true))
     return V;
- 
+
   // This only handles icmp of constants: (icmp1 A, C1) | (icmp2 B, C2).
   if (!LHSCst || !RHSCst) return nullptr;
 
@@ -2748,5 +2748,18 @@
       }
   }
 
+  // If we are XORing the sign bit of a floating-point value, convert
+  // this to fsub from -0.0, then cast back to integer.
+  ConstantInt *CI;
+  if (CastInst *Op0C = dyn_cast<CastInst>(Op0)) {
+    Type *SrcTy = Op0C->getOperand(0)->getType();
+    if (isa<BitCastInst>(Op0C) && SrcTy->isFloatingPointTy() &&
+          match(Op1, m_ConstantInt(CI)) && CI->isMinValue(true)) {
+        Value *Call = Builder->CreateFSub(
+            ConstantFP::getNegativeZero(SrcTy), Op0C->getOperand(0));
+        return CastInst::CreateBitOrPointerCast(Call, I.getType());
+    }
+  }
+
   return Changed ? &I : nullptr;
 }
Index: test/Transforms/InstCombine/xor2.ll
===================================================================
--- test/Transforms/InstCombine/xor2.ll
+++ test/Transforms/InstCombine/xor2.ll
@@ -23,7 +23,7 @@
 define i32 @test2(i32 %tmp1) {
 ; CHECK-LABEL:      @test2(
 ; CHECK-NEXT:   and i32 %tmp1, 32
-; CHECK-NEXT:   or i32 %ovm, 8 
+; CHECK-NEXT:   or i32 %ovm, 8
 ; CHECK-NEXT:   ret i32
         %ovm = and i32 %tmp1, 32
         %ov3 = add i32 %ovm, 145
@@ -36,7 +36,7 @@
 ; CHECK-NEXT:   and i32 %tmp1, 32
 ; CHECK-NEXT:   or i32 %ovm, 8
 ; CHECK-NEXT:   ret i32
-  %ovm = or i32 %tmp1, 145 
+  %ovm = or i32 %tmp1, 145
   %ov31 = and i32 %ovm, 177
   %ov110 = xor i32 %ov31, 153
   ret i32 %ov110
@@ -68,7 +68,7 @@
 }
 
 ; defect-1 in rdar://12329730
-; Simplify (X^Y) -> X or Y in the user's context if we know that 
+; Simplify (X^Y) -> X or Y in the user's context if we know that
 ; only bits from X or Y are demanded.
 ; e.g. the "x ^ 1234" can be optimized into x in the context of "t >> 16".
 ;  Put in other word, t >> 16 -> x >> 16.
@@ -172,3 +172,46 @@
 ; CHECK-NEXT: %[[xor:.*]] = xor i32 %[[and]], %c
 ; CHECK-NEXT: ret i32 %[[xor]]
 }
+
+
+define i64 @fsub_double(double %x) {
+; CHECK-LABEL: @fsub_double(
+; CHECK-NEXT:  %1 = fsub double -0.000000e+00, %x
+; CHECK-NEXT:  %xor = bitcast double %1 to i64
+; CHECK-NEXT:  ret i64 %xor
+  %bc = bitcast double %x to i64
+  %xor = xor i64 %bc, -9223372036854775808
+  ret i64 %xor
+}
+
+define i64 @fsub_double_swap(double %x) {
+; CHECK-LABEL: @fsub_double_swap(
+; CHECK-NEXT:  %1 = fsub double -0.000000e+00, %x
+; CHECK-NEXT:  %xor = bitcast double %1 to i64
+; CHECK-NEXT:  ret i64 %xor
+  %bc = bitcast double %x to i64
+  %xor = xor i64 -9223372036854775808, %bc
+  ret i64 %xor
+}
+
+define i32 @fsub_float(float %x) {
+; CHECK-LABEL: @fsub_float(
+; CHECK-NEXT:  %1 = fsub float -0.000000e+00, %x
+; CHECK-NEXT:  %xor = bitcast float %1 to i32
+; CHECK-NEXT:  ret i32 %xor
+  %bc = bitcast float %x to i32
+  %xor = xor i32 %bc, -2147483648
+  ret i32 %xor
+}
+
+; Make sure that only a bitcast is transformed.
+
+define i64 @fsub_double_not_bitcast(double %x) {
+; CHECK-LABEL: @fsub_double_not_bitcast(
+; CHECK-NEXT:  %bc = fptoui double %x to i64
+; CHECK-NEXT:  %xor = xor i64 %bc, -9223372036854775808
+; CHECK-NEXT:  ret i64 %xor
+  %bc = fptoui double %x to i64
+  %xor = xor i64 %bc, -9223372036854775808
+  ret i64 %xor
+}