diff --git a/llvm/include/llvm/Support/Alignment.h b/llvm/include/llvm/Support/Alignment.h --- a/llvm/include/llvm/Support/Alignment.h +++ b/llvm/include/llvm/Support/Alignment.h @@ -161,7 +161,17 @@ /// Returns a multiple of A needed to store `Size` bytes. inline uint64_t alignTo(uint64_t Size, Align A) { - return (Size + A.value() - 1) / A.value() * A.value(); + const uint64_t value = A.value(); + // The following line is equivalent to `(Size + value - 1) / value * value`. + + // The division followed by a multiplication can be thought of as a right + // shift followed by a left shift which zeros out the extra bits produced in + // the bump; `~(value - 1)` is a mask where all those bits being zeroed out + // are just zero. + + // Most compilers can generate this code but the pattern may be missed when + // multiple functions gets inlined. + return (Size + value - 1) & ~(value - 1); } /// Returns a multiple of A needed to store `Size` bytes.