Please note that I do not trust the “Suppress JIT optimization on module load” option, I spawn the process without debugging and attach my debugger after the JIT has run. In the version where single-line runs faster, this is Main: SingleLineTest(); 00000000 push ebp 00000001 mov ebp,esp 00000003 call dword ptr ds:[0019380Ch] MultiLineTest(); 00000009 call … Read more
-fomit-frame-pointer allows one extra register to be available for general-purpose use. I would assume this is really only a big deal on 32-bit x86, which is a bit starved for registers.* One would expect to see EBP no longer saved and adjusted on every function call, and probably some additional use of EBP in normal … Read more
You can make any of these work. I prefer the union layout, because then all nodes have “the same” layout. [You may find it useful to have a “child sublist” option, e.g., and arbitarily big, dynamic array of children, instead of having left- or right-leaning lists.] You are going to find that this issue isn’t … Read more
I think I’d be tempted to flag that Wikipedia quote with [citation needed]; the assumptions are, at least, questionable. For example, there are a large number of compiler-construction tools based on yacc which make it extremely easy, in practice, to construct a parser using the more powerful (and equally fast) LALR algorithm, and some also … Read more
Dr. Dobbs just published an article by Walter Bright (of dlang fame), where he mentions the term: Lowering One semantic technique that is obvious in hindsight (but took Andrei Alexandrescu to point out to me) is called “lowering.” It consists of, internally, rewriting more complex semantic constructs in terms of simpler ones. For example, while … Read more
Neither /\ nor / are defined as operators in the ISO C89 standard, and I don’t think they were ever defined in any earlier version. And they are definitely not defined in C99 as far as I know. Here’s a draft of the ANSI C89 standard, for reference: http://flash-gordon.me.uk/ansi.c.txt (You are likely a victim of … Read more
Yes, there certainly are such scenarios. JIT compilation can use runtime profiling to optimize specific cases based on measurement of the characteristics of what the code is actually doing at the moment, and can recompile “hot” code as necessary. That’s not theoretical; Java’s HotSpot actually does this. JITters can optimize for the specific CPU and … Read more
You need to use a version of the cl.exe compiler which emits x64 code. Which one depends a bit on your setup. Let’s consider the case you’re on a 64 bit machine. For this you’ll need to use the compiler which lives at c:\Program Files (x86)\Microsoft visual Studio 10.0\VC\bin\amd64\cl.exe If you’re on a 32 bit … Read more
Actually VS2008 optimizes this to x+x: 01391000 push ecx int x = 0; scanf(“%d”, &x); 01391001 lea eax,[esp] 01391004 push eax 01391005 push offset string “%d” (13920F4h) 0139100A mov dword ptr [esp+8],0 01391012 call dword ptr [__imp__scanf (13920A4h)] int y = x * 2; 01391018 mov ecx,dword ptr [esp+8] 0139101C lea edx,[ecx+ecx] In an x64 … Read more
Macros are simply textual substitution, so in your example writing TIMER_100_MS in a program is a fancy way of writing 32768 / 10. Therefore, the question is when the compiler would evaluate 32768 / 10, which is a constant integral expression. I don’t think the standard requires any particular behavior here (since run-time and compile-time … Read more