From a4306b9e5662fca74f65f0b657e7002fda7f1829 Mon Sep 17 00:00:00 2001
From: Marshall Mohror <mohror64@gmail.com>
Date: Tue, 7 Jul 2020 16:39:23 -0500
Subject: [PATCH] Common: remove a mod from AlignUp (#5441)
In cases where the size is not a known constant when inlining, AlignUp<std::size_t> currently generates two 64-bit div instructions.
This generates one div and a cmov which is significantly cheaper.
---
src/common/alignment.h | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/src/common/alignment.h b/src/common/alignment.h
index f8c49e079..516bb26c1 100644
--- a/src/common/alignment.h
+++ b/src/common/alignment.h
@@ -11,7 +11,9 @@ namespace Common {
template <typename T>
constexpr T AlignUp(T value, std::size_t size) {
static_assert(std::is_unsigned_v<T>, "T must be an unsigned value.");
- return static_cast<T>(value + (size - value % size) % size);
+ auto mod{value % size};
+ value -= mod;
+ return static_cast<T>(mod == T{0} ? value : value + size);
}
template <typename T>