Could the compiler invalidate twoSum ?
nestordemeure opened this issue · comments
Hello,
It is usually said that aggressive compilation might invalidate twoSum.
In libeft, the only guard against this phenomenon that I could find is a pragma GCC to avoid O3 compilation, is this enough ?
It might be : even gcc -Ofast -ffast-math was not able to invalidate a similar implementation of this EFT on my machine. I will try the Intel compiler as soon as I get my hand on it...
Cordially,
Nestor Demeure
You are right: aggressive compiler optimizations can invalidate twoSum.
At the time when I implemented the original version of libeft, the pragmas were enough for the gcc version I was using. Since then, I have seen cases where gcc -O3 or gcc -O2 made optimizations which would invalidate twoSum.
A more robust implementation has been introduced in commit 74e4097, which uses intrinsics for all sensitive FP operations in twoSum, twoProd and split. With this version (currently accessible in the dev branch), twoSum and twoProd seem to remain valid, even with aggressive compiler optimizations (-O3, -Ofast or -ffast-math for gcc).
branch dev has now been merged into master.