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Comment: Re:Q: Why Are Scientists Still Using FORTRAN in 20 (Score 2) 634

by dumael (#46966539) Attached to: Why Scientists Are Still Using FORTRAN in 2014

> Fortran code ignores the very possibility that pointer content can overlap. Modern compilers do not.

Fortran's language specification doesn't allow pointers to overlap. Inhibiting programmer freedom in this way ironically gives the compiler greater freedom to perform optimizations.

In contrast C & co, give the programmer this freedom, resulting in the compiler having to be more conservative.

Comment: Re:not in the field, eh? (Score 1) 634

by dumael (#46966485) Attached to: Why Scientists Are Still Using FORTRAN in 2014
Language semantics are the real difference. To get comparable semantics in a C program and a Fortran program solving the same problem, the C program has to use the "restrict" keyword everywhere (or nearly everywhere/or where it counts). Fortran by default disallows aliasing (the purpose of restrict) in contrast to C.

Location aliasing inhibits intermediate code[1] optimization as the optimizer cannot assume that two pointers point to difference locations. If the optimizer can safely make that assumption it can do more with the code.

Aside: during my compiler design class, the lecturer spent time going over some optimizations (obviously). Towards the end of the lecture: "oh but if p aliases q, you cannot use that optimization".

[1] Any compiler worth its use translates input files into some form of intermediate representation for optimization purposes.

Comment: Re:Popular has a lot to do with installed base... (Score 1) 634

by dumael (#46966335) Attached to: Why Scientists Are Still Using FORTRAN in 2014
Fortran doesn't restrict multiple threads accessing the same array (see OpenMP), instead it restricts how pointers may be used. A frequent problem with program optimization is that if two or more pointers address the same location, it is aliased.

This wrecks havoc as the compiler can no longer assume some optimizations are safe.

Otherwise your post is mostly correct.

Comment: Re:Isn't this part of what VLIW has already tried? (Score 1) 404

by dumael (#42190283) Attached to: Auto-threading Compiler Could Restore Moore's Law Gains
Afaik, the problem with VLIW processors in general is that they attempt to exploit instruction-level parallelism.

This is an entirely different beast to what's presented in the paper.

Instruction-level parallelism occurs when there are instructions within a (fixed) window of a code stream where there are no dependencies between two or more instructions.

The VLIW paradigm is have bundles of instructions which contain all instructions that can be executed simultaneously. This shifts complexity from the hardware[1] to the compiler.

Unfortunately, ILP can be very difficult to extract from arbitrary code, though cases exist where it's trivial.

[1] Latter RISC chips and today's non-mobile CPUs take advantage of ILP through the use of multi-issue out of order execution. Out-of-order execution typically defers execution of any given instruction until all its dependencies have been fulfilled i.e. memory/cache accesses have occurred, previous results are available, etc. By making these units multi-issue the CPU dynamically exploits ILP to the availability of hardware, no recompilation required (though it may help).

These hardware techniques are slowly coming to the mobile arena as they are relatively expensive transistor wise.

Comment: Re:This is a stupid article (Score 1) 402

by dumael (#39937471) Attached to: Why You Can't Dump Java (Even Though You Want To)
> Maybe Oracle can actually expand Java. Oracle owns silicon, so why not make a processor that is designed from the ground up for Java bytecode? Perhaps even build it into the SPARC architecture . ARM tried it with Jazelle in earlier cores which they've replaced with the ThumbEE and successor. JIT compilers (and in ARM's case simpler+compact instructions) seem to have been more economical than implementing a (partial) second instruction set in a processor and requiring to be at least as fast the JIT competition.

Comment: Re:This is what's wrong with private healthcare. (Score 2) 646

by dumael (#38531784) Attached to: How Doctors Die
Really?

http://www.irishdentist.ie/news/news_detail.php?id=3969

Mind you this was a walk-in procedure, not an impacted tooth or anything. And it definitely wasn't subisidized by the Irish government (that's where you get a discount for paying PRSI). Which appears to have been cut.

Leaching indirectly off insurance companies? That'd be interesting given the VHI tend to refund costs of low priced stuff to the you directly afaik.

Comment: Re:This is what's wrong with private healthcare. (Score 1) 646

by dumael (#38531300) Attached to: How Doctors Die
A $1000 dollars for a wisdom tooth extraction? I had one extracted in Ireland as a walk-in patient. No insurance mentioned, no PRSI slips shown.

60 Euro. And that included an X-Ray to say, "Yes, that tooth is pretty much irrecoverable".

And I probably could have gotten it performed cheaper outside the capital.

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