more inline assembler noise

Hello, Again, apologies for prematurely declaring someone else's code 'crap'. There are no bugs in the inline x86 assembler in Zend/zend_operators.h, as far as I can tell, only two kinds of issues that I still think should be addressed. First of all, from a maintenance pov, having field offsets (like the offset of zval.type) and constants (like $0x2 for IS_DOUBLE) hard coded inside the instructions is a bad idea. The other issue is the branching and the floating point instructions. The inline assembler addresses the common case, but also adds a bunch of instructions that address the corner case, and some branches to jump over them. As I indicated in my previous email, branching is relatively costly on a modern CPU with deep pipelines and having a bunch of FPU instructions in there that hardly ever get executed doesn't help either. The primary reason for having inline assembler at all is the ability to detect overflow. This mainly applies to multiplication, as in that case, detecting overflow in C code is much harder compared to reading a condition flag in the CPU (hence the various accelerated implementations in zend_signed_multiply.h). However, detecting overflow in addition/subtraction implemented in C is much easier, as the code in zend_operators.h proves: just a matter of checking the sign bits, or doing a simple compare with LONG_MIN/LONG_MAX. Therefore, I would be interested in finding out which benchmark was used to make the case for having these accelerated implementations in the first place. The differences in performance between various implementations are very small in the tests I have done. As for the code style/maintainability, I propose to apply the attached patch. The performance is on par, as far as I can tell, but it is arguably better code. I will also hook in the ARM versions once I manage to prove that the performance is affected favourably by them. Regards, Ard. Before ------- $ time php -r 'for ($i = 0; $i < 0x7fffffff; $i++);' real 0m56.910s user 0m56.876s sys 0m0.008s $ time php -r 'for ($i = 0x7fffffff; $i >= 0; $i--);' real 1m34.576s user 1m34.518s sys 0m0.020s $ time php -r 'for ($i = 0; $i < 0x7fffffff; $i += 3);' real 0m21.494s user 0m21.473s sys 0m0.008s $ time php -r 'for ($i = 0x7fffffff; $i >= 0; $i -= 3);' real 0m19.879s user 0m19.865s sys 0m0.004s After ----- $ time php -r 'for ($i = 0; $i < 0x7fffffff; $i++);' real 0m56.687s user 0m56.656s sys 0m0.004s $ time php -r 'for ($i = 0x7fffffff; $i >= 0; $i--);' real 1m28.124s user 1m28.082s sys 0m0.004s $ time php -r 'for ($i = 0; $i < 0x7fffffff; $i += 3);' real 0m20.561s user 0m20.545s sys 0m0.004s $ time php -r 'for ($i = 0x7fffffff; $i >= 0; $i -= 3);' real 0m20.524s user 0m20.509s sys 0m0.004s

Attachment: [text/x-patch] 0001-Improve-x86-assembler-implementations-of-add-sub-int.patch