9. What Compilers Can and Cannot Do 

*My takeaways:* 1. Why study the compiler optimizations? 4:05 2. Simple model of the compiler 8:30 3. Compiler report 9:33 4. Overview of compiler optimizations 13:20 5. Example compiler optimizations 26:00 - Optimizing a scalar 30:20 - Optimizing a structure 33:56 - Optimizing function calls 43:10 - Optimizing loops 56:05 6. WHat compilers can and cannot do 1:04:25 7. Diagnosing failures: case studies 1:06:30

Those times when the compiler de-optimizes sections of your code or introduces elusive "bugs" in your code, similar to what happened to me when the MFC were still in development and I was programming for Win NT, the good "o'l" times.

@25:43, the reason for choosing 38 is because it's a dealing with a 32-bit integer on a 64-bit register, so we have an extra 32 bits to play with. 71 > 64 = 2^6, so magic_num = 2^38/71 is definitely less than 2^32, so num_32 * magic_num shifts the top bit by no more than num_32

what a great teacher! thank you!

This is a great lecture

I'm glad I don't have to write a compiler 😉🙏

A compiler appears to choose optimal decision branches based upon the choices available. This methodology is similar to substitution networks in theorem provers. Perhaps theorem provers built into compilers will become the first A.I. driven constructs to achieve true sentience and artificial intelligence. Imagine a compiler that understands algebra, philosophy, and all scientific topics, including physics. With the ability to generate and reason over its own code, the compiler would become the ultimate decision maker.

Ahem, the problem at 1:06:00 is very much optimizable by looking at a computation graph and seeing that the two sequences for F12 and -F21 are algebraically equivalent, without needing to know physics.

13:30 yeah not gonna lie they got us in the first half

Fantastic content. Chapeau to the tutor.

I just saw the video "restrict: the only C keyword with no C++ equivalent" - inexplicably, I'd never seen the restrict keyword before.

Thank you for this course. :)

For anyone wondering, eax is lower 32 bits of rax

Thank you for these lectures, this one was absolutely amazing 🎉

teacher is beyond smart! Great lecture!

"What about GCC? I have a 20 thousand line DIVINE intellect compiler that operates Just In Time AND ahead of time."

Watched this video to understand minisicule things in Optimization by compiler...hope this give me clear understanding in design of compilers and for my gate prep..

What frustrates me is that compilers don't take advantage of advanced instruction intrinsics automatically enough -- most of the modern CPU optimized SIMD/AVX instructions go unused. You have to manually construct SIMD usage most of the time which makes it a fools errand most of the time unless you're compiling code for your own system. If you're going to distribute compiled software, you have to dumb it down to a neutral architecture that doesn't risk using unsupported opcodes on the target system.

As a compiler engineer, i was interested in the part where professor describes what compilers can't do. And what he describes appears to be true! It will be a real challenge to establish if two forces cancel each other. We could certainly encode rules (or laws of Physics for this example) as type constraints and then compiler may be able to figure that out but that is probably years ahead of the scope of modern compilers.

He even looks like a genious :)

The greatest computer language to develop a Lexical Analyzer and a Compiler for any computer language is CPython hands down. In fact CPython's Regular Expression re.sub() methods and string replace methods work in multiple algorithms nested and can handle the heavy lifting end of both exceptionally well. Under 280 lines of code will do both, and do some things today's compilers cannot do.

I don't know why RU-vid recommended this to me, but I stayed for the whole lecture.

I just realized why the '32 seconds' timing claim is wrong. Now, we can presume the processor has 16 cores, each with only one thread, that could execute 32 billion instructions per second. Except for one thing. Memory. Fastest memory DDR4-4400 has sustained transfer rate 4.4 gb/sec, throttling processors to that., and, ia64/AMD64 instructions run from 1-15 bytes each. If we estimate an average of 4 bytes per instruction, at that rate it requires 40 terabytes of ram, and that would require 4,000 seconds (6 1/2 hours) at the 4.4 ghz rate. Now there is a burst speed of 35gb/sec, so if you could run the memory that fast, at the 35gb/sec burst rate (and I don't think you'd get burst speed continuously) it would take about 120 seconds.

17:06

Werever dando clases.

Hacker's delight book

The guy stands there looking lime an über-dork in his charlie-chaplin pants and with the stupid beard, if you can call it that... Then he starts to talk, and my god. Perception totally changes, suddenly he's an athletic giant, lol. 👍 Intellect is attractive. 👍

Ok I I

please, if you are not difficult tell me the main conclusion of this video in one minute. please

You have to be kind of sick in the head to think studying how a compiler works is fun ;). It is quite interesting, but it's definitely not "fun" for the average engineer/computer scientist. I guess that's why he's at MIT lol.

But what is his education, CV? -- Er. Sunil Pedgaonkar, India, Consulting Engineer (IT), India

Here for neymar