diff --git a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
index e64d3f5..c3b6b30 100644
--- a/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/LegalizerHelper.cpp
@@ -7169,6 +7169,78 @@
   return Legalized;
 }
 
+// Expand s32 = G_UITOFP s64 to an IEEE float representation using bit
+// operations and G_SITOFP
+LegalizerHelper::LegalizeResult
+LegalizerHelper::lowerU64ToF32WithSITOFP(MachineInstr &MI) {
+  auto [Dst, Src] = MI.getFirst2Regs();
+  const LLT S64 = LLT::scalar(64);
+  const LLT S32 = LLT::scalar(32);
+  const LLT S1 = LLT::scalar(1);
+
+  assert(MRI.getType(Src) == S64 && MRI.getType(Dst) == S32);
+
+  // For i64 < INT_MAX we simply reuse SITOFP.
+  // Otherwise, divide i64 by 2, round result by ORing with the lowest bit
+  // saved before division, convert to float by SITOFP, multiply the result
+  // by 2.
+  auto One = MIRBuilder.buildConstant(S64, 1);
+  auto Zero = MIRBuilder.buildConstant(S64, 0);
+  // Result if Src < INT_MAX
+  auto SmallResult = MIRBuilder.buildSITOFP(S32, Src);
+  // Result if Src >= INT_MAX
+  auto Halved = MIRBuilder.buildLShr(S64, Src, One);
+  auto LowerBit = MIRBuilder.buildAnd(S64, Src, One);
+  auto RoundedHalved = MIRBuilder.buildOr(S64, Halved, LowerBit);
+  auto HalvedFP = MIRBuilder.buildSITOFP(S32, RoundedHalved);
+  auto LargeResult = MIRBuilder.buildFAdd(S32, HalvedFP, HalvedFP);
+  // Check if the original value is larger than INT_MAX by comparing with
+  // zero to pick one of the two conversions.
+  auto IsLarge =
+      MIRBuilder.buildICmp(CmpInst::Predicate::ICMP_SLT, S1, Src, Zero);
+  MIRBuilder.buildSelect(Dst, IsLarge, LargeResult, SmallResult);
+
+  MI.eraseFromParent();
+  return Legalized;
+}
+
+// Expand s64 = G_UITOFP s64 using bit and float arithmetic operations to an
+// IEEE double representation.
+LegalizerHelper::LegalizeResult
+LegalizerHelper::lowerU64ToF64BitFloatOps(MachineInstr &MI) {
+  auto [Dst, Src] = MI.getFirst2Regs();
+  const LLT S64 = LLT::scalar(64);
+  const LLT S32 = LLT::scalar(32);
+
+  assert(MRI.getType(Src) == S64 && MRI.getType(Dst) == S64);
+
+  // We create double value from 32 bit parts with 32 exponent difference.
+  // Note that + and - are float operations that adjust the implicit leading
+  // one, the bases 2^52 and 2^84 are for illustrative purposes.
+  //
+  // X = 2^52 * 1.0...LowBits
+  // Y = 2^84 * 1.0...HighBits
+  // Scratch = 2^84 * 1.0...HighBits - 2^84 * 1.0 - 2^52 * 1.0
+  //         = - 2^52 * 1.0...HighBits
+  // Result = - 2^52 * 1.0...HighBits + 2^52 * 1.0...LowBits
+  auto TwoP52 = MIRBuilder.buildConstant(S64, UINT64_C(0x4330000000000000));
+  auto TwoP84 = MIRBuilder.buildConstant(S64, UINT64_C(0x4530000000000000));
+  auto TwoP52P84 = llvm::bit_cast<double>(UINT64_C(0x4530000000100000));
+  auto TwoP52P84FP = MIRBuilder.buildFConstant(S64, TwoP52P84);
+  auto HalfWidth = MIRBuilder.buildConstant(S64, 32);
+
+  auto LowBits = MIRBuilder.buildTrunc(S32, Src);
+  LowBits = MIRBuilder.buildZExt(S64, LowBits);
+  auto LowBitsFP = MIRBuilder.buildOr(S64, TwoP52, LowBits);
+  auto HighBits = MIRBuilder.buildLShr(S64, Src, HalfWidth);
+  auto HighBitsFP = MIRBuilder.buildOr(S64, TwoP84, HighBits);
+  auto Scratch = MIRBuilder.buildFSub(S64, HighBitsFP, TwoP52P84FP);
+  MIRBuilder.buildFAdd(Dst, Scratch, LowBitsFP);
+
+  MI.eraseFromParent();
+  return Legalized;
+}
+
 LegalizerHelper::LegalizeResult LegalizerHelper::lowerUITOFP(MachineInstr &MI) {
   auto [Dst, DstTy, Src, SrcTy] = MI.getFirst2RegLLTs();
 
@@ -7183,13 +7255,15 @@
   if (SrcTy != LLT::scalar(64))
     return UnableToLegalize;
 
-  if (DstTy == LLT::scalar(32)) {
+  if (DstTy == LLT::scalar(32))
     // TODO: SelectionDAG has several alternative expansions to port which may
-    // be more reasonble depending on the available instructions. If a target
-    // has sitofp, does not have CTLZ, or can efficiently use f64 as an
-    // intermediate type, this is probably worse.
-    return lowerU64ToF32BitOps(MI);
-  }
+    // be more reasonable depending on the available instructions. We also need
+    // a more advanced mechanism to choose an optimal version depending on
+    // target features such as sitofp or CTLZ availability.
+    return lowerU64ToF32WithSITOFP(MI);
+
+  if (DstTy == LLT::scalar(64))
+    return lowerU64ToF64BitFloatOps(MI);
 
   return UnableToLegalize;
 }