From b7e6b1ab7029b45f0be81f3026e571f9977dc5c3 Mon Sep 17 00:00:00 2001 From: Chris Lattner Date: Thu, 15 Nov 2007 04:51:31 +0000 Subject: many edits, patch by Kelly Wilson! git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@44157 91177308-0d34-0410-b5e6-96231b3b80d8 --- docs/tutorial/LangImpl8.html | 36 ++++++++++++++++++------------------ 1 file changed, 18 insertions(+), 18 deletions(-) (limited to 'docs/tutorial/LangImpl8.html') diff --git a/docs/tutorial/LangImpl8.html b/docs/tutorial/LangImpl8.html index d84dfdc..855b8f3 100644 --- a/docs/tutorial/LangImpl8.html +++ b/docs/tutorial/LangImpl8.html @@ -98,7 +98,7 @@ Programmer's Manual that describes how to construct them.

standard runtime - Our current language allows the user to access arbitrary external functions, and we use it for things like "printd" and "putchard". As you extend the language to add higher-level constructs, often -these constructs make the most amount of sense to be lowered into calls into a +these constructs make the most sense if they are lowered to calls into a language-supplied runtime. For example, if you add hash tables to the language, it would probably make sense to add the routines to a runtime, instead of inlining them all the way.

@@ -106,14 +106,14 @@ inlining them all the way.

memory management - Currently we can only access the stack in Kaleidoscope. It would also be useful to be able to allocate heap memory, either with calls to the standard libc malloc/free interface or with a garbage -collector. If you choose to use garbage collection, note that LLVM fully +collector. If you would like to use garbage collection, note that LLVM fully supports Accurate Garbage Collection including algorithms that move objects and need to scan/update the stack.

debugger support - LLVM supports generation of DWARF Debug info which is understood by common debuggers like GDB. Adding support for debug info is fairly -straight-forward. The best way to understand it is to compile some C/C++ code +straightforward. The best way to understand it is to compile some C/C++ code with "llvm-gcc -g -O0" and taking a look at what it produces.

exception handling support - LLVM supports generation of

Have fun - try doing something crazy and unusual. Building a language like -everyone else always has is much less fun than trying something a little crazy -and off the wall and seeing how it turns out. If you get stuck or want to talk +everyone else always has, is much less fun than trying something a little crazy +or off the wall and seeing how it turns out. If you get stuck or want to talk about it, feel free to email the llvmdev mailing list: it has lots of people who are interested in languages and are often willing to help out.

Before we end, I want to talk about some "tips and tricks" for generating +

Before we end this tutorial, I want to talk about some "tips and tricks" for generating LLVM IR. These are some of the more subtle things that may not be obvious, but are very useful if you want to take advantage of LLVM's capabilities.

Properties of LLVM +

Properties of the LLVM IR

@@ -184,7 +184,7 @@ compiling that on targets that LLVM doesn't support natively. You can trivially tell that the Kaleidoscope compiler generates target-independent code because it never queries for any target-specific information when generating code.

The fact that LLVM provides a compact target-independent representation for +

The fact that LLVM provides a compact, target-independent, representation for code gets a lot of people excited. Unfortunately, these people are usually thinking about C or a language from the C family when they are asking questions about language portability. I say "unfortunately", because there is really no @@ -208,7 +208,7 @@ the input text:

While it is possible to engineer more and more complex solutions to problems -like this, it cannot be solved in full generality in a way better than shipping +like this, it cannot be solved in full generality in a way that is better than shipping the actual source code.

That said, there are interesting subsets of C that can be made portable. If @@ -263,7 +263,7 @@ few observations:

writing, there is no way to distinguish in the LLVM IR whether an SSA-value came from a C "int" or a C "long" on an ILP32 machine (other than debug info). Both get compiled down to an 'i32' value and the information about what it came from -is lost. The more general issue here is that the LLVM type system uses +is lost. The more general issue here, is that the LLVM type system uses "structural equivalence" instead of "name equivalence". Another place this surprises people is if you have two types in a high-level language that have the same structure (e.g. two different structs that have a single int field): these @@ -275,10 +275,10 @@ continue to enhance and improve it in many different ways. In addition to adding new features (LLVM did not always support exceptions or debug info), we also extend the IR to capture important information for optimization (e.g. whether an argument is sign or zero extended, information about pointers -aliasing, etc. Many of the enhancements are user-driven: people want LLVM to -do some specific feature, so they go ahead and extend it to do so.

+aliasing, etc). Many of the enhancements are user-driven: people want LLVM to +include some specific feature, so they go ahead and extend it.

Third, it is possible and easy to add language-specific +

Third, it is possible and easy to add language-specific optimizations, and you have a number of choices in how to do it. As one trivial example, it is easy to add language-specific optimization passes that "know" things about code compiled for a language. In the case of the C family, @@ -291,7 +291,7 @@ function does.

other language-specific information into the LLVM IR. If you have a specific need and run into a wall, please bring the topic up on the llvmdev list. At the very worst, you can always treat LLVM as if it were a "dumb code generator" and -implement the high-level optimizations you desire in your front-end on the +implement the high-level optimizations you desire in your front-end, on the language-specific AST.

@@ -316,8 +316,8 @@ offsetof/sizeof

One interesting thing that comes up if you are trying to keep the code -generated by your compiler "target independent" is that you often need to know +

One interesting thing that comes up, if you are trying to keep the code +generated by your compiler "target independent", is that you often need to know the size of some LLVM type or the offset of some field in an llvm structure. For example, you might need to pass the size of a type into a function that allocates memory.

@@ -342,10 +342,10 @@ they are garbage collected or to allow easy implementation of closures. There are often better ways to implement these features than explicit stack frames, but LLVM -does support them if you want. It requires your front-end to convert the +does support them, if you want. It requires your front-end to convert the code into Continuation -Passing Style and use of tail calls (which LLVM also supports).

+Passing Style and the use of tail calls (which LLVM also supports).

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