ADT: add <bit> header, implement C++20 bit_cast, use
Summary: I saw a few places that were punning through a union of FP and integer, and that made me sad. Luckily, C++20 adds bit_cast for exactly that purpose. Implement our own version in ADT (without constexpr, leaving us a bit sad), and use it in the few places my grep-fu found silly union punning.
This was originally committed as r341728 and reverted in r341730.
Reviewers: javed.absar, steven_wu, srhines
Subscribers: dexonsmith, llvm-commits
Differential Revision: https://reviews.llvm.org/D51693
llvm-svn: 341741
diff --git a/llvm/lib/Support/APInt.cpp b/llvm/lib/Support/APInt.cpp
index f3c2ca5..f2f5cca 100644
--- a/llvm/lib/Support/APInt.cpp
+++ b/llvm/lib/Support/APInt.cpp
@@ -19,6 +19,7 @@
#include "llvm/ADT/Optional.h"
#include "llvm/ADT/SmallString.h"
#include "llvm/ADT/StringRef.h"
+#include "llvm/ADT/bit.h"
#include "llvm/Config/llvm-config.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/ErrorHandling.h"
@@ -712,24 +713,20 @@
}
APInt llvm::APIntOps::RoundDoubleToAPInt(double Double, unsigned width) {
- union {
- double D;
- uint64_t I;
- } T;
- T.D = Double;
+ uint64_t I = bit_cast<uint64_t>(Double);
// Get the sign bit from the highest order bit
- bool isNeg = T.I >> 63;
+ bool isNeg = I >> 63;
// Get the 11-bit exponent and adjust for the 1023 bit bias
- int64_t exp = ((T.I >> 52) & 0x7ff) - 1023;
+ int64_t exp = ((I >> 52) & 0x7ff) - 1023;
// If the exponent is negative, the value is < 0 so just return 0.
if (exp < 0)
return APInt(width, 0u);
// Extract the mantissa by clearing the top 12 bits (sign + exponent).
- uint64_t mantissa = (T.I & (~0ULL >> 12)) | 1ULL << 52;
+ uint64_t mantissa = (I & (~0ULL >> 12)) | 1ULL << 52;
// If the exponent doesn't shift all bits out of the mantissa
if (exp < 52)
@@ -806,12 +803,8 @@
// The leading bit of mantissa is implicit, so get rid of it.
uint64_t sign = isNeg ? (1ULL << (APINT_BITS_PER_WORD - 1)) : 0;
- union {
- double D;
- uint64_t I;
- } T;
- T.I = sign | (exp << 52) | mantissa;
- return T.D;
+ uint64_t I = sign | (exp << 52) | mantissa;
+ return bit_cast<double>(I);
}
// Truncate to new width.