[llvm] r290715 - [ADT] Use memcpy for type punning in MathExtras.

[Justin Lebar via llvm-commits]

Author: jlebar
Date: Thu Dec 29 12:15:34 2016
New Revision: 290715

URL: http://llvm.org/viewvc/llvm-project?rev=290715&view=rev
Log:
[ADT] Use memcpy for type punning in MathExtras.

Summary: Previously we type-punned through a union, which is not safe.

Reviewers: rnk

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D28161

Modified:
    llvm/trunk/include/llvm/Support/MathExtras.h

Modified: llvm/trunk/include/llvm/Support/MathExtras.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/Support/MathExtras.h?rev=290715&r1=290714&r2=290715&view=diff
==============================================================================
--- llvm/trunk/include/llvm/Support/MathExtras.h (original)
+++ llvm/trunk/include/llvm/Support/MathExtras.h Thu Dec 29 12:15:34 2016
@@ -547,23 +547,19 @@ inline uint64_t GreatestCommonDivisor64(
 /// BitsToDouble - This function takes a 64-bit integer and returns the bit
 /// equivalent double.
 inline double BitsToDouble(uint64_t Bits) {
-  union {
-    uint64_t L;
-    double D;
-  } T;
-  T.L = Bits;
-  return T.D;
+  double D;
+  static_assert(sizeof(uint64_t) == sizeof(double), "Unexpected type sizes");
+  memcpy(&D, &Bits, sizeof(Bits));
+  return D;
 }
 
 /// BitsToFloat - This function takes a 32-bit integer and returns the bit
 /// equivalent float.
 inline float BitsToFloat(uint32_t Bits) {
-  union {
-    uint32_t I;
-    float F;
-  } T;
-  T.I = Bits;
-  return T.F;
+  float F;
+  static_assert(sizeof(uint32_t) == sizeof(float), "Unexpected type sizes");
+  memcpy(&F, &Bits, sizeof(Bits));
+  return F;
 }
 
 /// DoubleToBits - This function takes a double and returns the bit
@@ -571,12 +567,10 @@ inline float BitsToFloat(uint32_t Bits)
 /// changes the bits of NaNs on some hosts, notably x86, so this
 /// routine cannot be used if these bits are needed.
 inline uint64_t DoubleToBits(double Double) {
-  union {
-    uint64_t L;
-    double D;
-  } T;
-  T.D = Double;
-  return T.L;
+  uint64_t Bits;
+  static_assert(sizeof(uint64_t) == sizeof(double), "Unexpected type sizes");
+  memcpy(&Bits, &Double, sizeof(Double));
+  return Bits;
 }
 
 /// FloatToBits - This function takes a float and returns the bit
@@ -584,12 +578,10 @@ inline uint64_t DoubleToBits(double Doub
 /// changes the bits of NaNs on some hosts, notably x86, so this
 /// routine cannot be used if these bits are needed.
 inline uint32_t FloatToBits(float Float) {
-  union {
-    uint32_t I;
-    float F;
-  } T;
-  T.F = Float;
-  return T.I;
+  uint32_t Bits;
+  static_assert(sizeof(uint32_t) == sizeof(float), "Unexpected type sizes");
+  memcpy(&Bits, &Float, sizeof(Float));
+  return Bits;
 }
 
 /// MinAlign - A and B are either alignments or offsets.  Return the minimum