Subzero: Fix g++ warnings.

src/IceInstARM32.cpp

Index: src/IceInstARM32.cpp
diff --git a/src/IceInstARM32.cpp b/src/IceInstARM32.cpp
index 075dd4d2c84e1eca9a24b6d6e6901be937feea1d..5a17abe101b46d0aef0fea61449ee6e46aad3cc9 100644
--- a/src/IceInstARM32.cpp
+++ b/src/IceInstARM32.cpp
@@ -347,7 +347,7 @@ bool OperandARM32FlexFpImm::canHoldImm(Operand *C, uint32_t *ModifiedImm) {
     static_assert(AllowedBits == 0xFFF80000u,
                   "Invalid mask for f32 modified immediates.");
     const float F32 = llvm::cast<ConstantFloat>(C)->getValue();
-    const uint32_t I32 = *reinterpret_cast<const uint32_t *>(&F32);
+    const uint32_t I32 = bit_copy<uint32_t>(F32);

[John, 2016/01/12 18:09:07]

this method (bit_copy) is "poorly" named. I thought there was an std::bit_copy
and, to my surprise, that does not exist.

When I found it, its implementation seems buggy:  D destination;

template <class D, class S> inline D bit_copy(const S &source) {
  // This use of memcpy is safe: source and destination cannot overlap.
  memcpy(&destination, reinterpret_cast<const void *>(&source),
         sizeof(destination));
  return destination;
}

I would think the size parameter should be

std::min(sizeof(destination), sizeof(source));

The method should also belong to the Ice::Utils namespace. Do you mind changing
these things? I know they are unrelated, but I fear this will never be changed
if we don't change it now.

[Jim Stichnoth, 2016/01/13 19:30:33]

Done.

     if (I32 & ~AllowedBits) {
       // constant has disallowed bits.
       return false;
@@ -376,7 +376,7 @@ bool OperandARM32FlexFpImm::canHoldImm(Operand *C, uint32_t *ModifiedImm) {
     static_assert(AllowedBits == 0xFFFF0000u,
                   "Invalid mask for f64 modified immediates.");
     const double F64 = llvm::cast<ConstantDouble>(C)->getValue();
-    const uint64_t I64 = *reinterpret_cast<const uint64_t *>(&F64);
+    const uint64_t I64 = bit_copy<uint64_t>(F64);
     if (I64 & 0xFFFFFFFFu) {
       // constant has disallowed bits.
       return false;
@@ -2100,7 +2100,7 @@ float materializeFloatImmediate(uint32_t ModifiedImm) {
   const uint32_t Ret = ((ModifiedImm & a) ? 0x80000000 : 0) |
                        ((ModifiedImm & b) ? 0x3E000000 : 0x40000000) |
                        ((ModifiedImm & cdefgh) << 19);
-  return *reinterpret_cast<const float *>(&Ret);
+  return bit_copy<float>(Ret);
 }
 
 } // end of anonymous namespace