diff options
| author | John Criswell <criswell@uiuc.edu> | 2003-12-16 16:56:10 +0000 |
|---|---|---|
| committer | John Criswell <criswell@uiuc.edu> | 2003-12-16 16:56:10 +0000 |
| commit | da45ebd298646700a4c5dead6eac0a171b5b490a (patch) | |
| tree | ab3506dfe6f70be0e259638072091bf01b7425f2 /llvm | |
| parent | 0dd5964f482643773aee4126f61b4584b5f54774 (diff) | |
| download | llvm-da45ebd298646700a4c5dead6eac0a171b5b490a.zip llvm-da45ebd298646700a4c5dead6eac0a171b5b490a.tar.gz llvm-da45ebd298646700a4c5dead6eac0a171b5b490a.tar.bz2 | |
Not ready for prime-time.
llvm-svn: 10485
Diffstat (limited to 'llvm')
| -rw-r--r-- | llvm/docs/LLVMVsTheWorld.html | 180 |
1 files changed, 0 insertions, 180 deletions
diff --git a/llvm/docs/LLVMVsTheWorld.html b/llvm/docs/LLVMVsTheWorld.html deleted file mode 100644 index a69ae20..0000000 --- a/llvm/docs/LLVMVsTheWorld.html +++ /dev/null @@ -1,180 +0,0 @@ -<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" - "http://www.w3.org/TR/html4/strict.dtd"> -<html> -<head> - <link rel="stylesheet" href="llvm.css" type="text/css"> - <title>LLVM vs. the World - Comparing Compilers to Compilers</title> -</head> - -<body> - -<div class="doc_title"> - LLVM vs. the World - Comparing Compilers to Compilers -</div> - -<ol> - <li><a href="#introduction">Introduction</a></li> - <li><a href="#generalapplicability">General Applicability</a></li> - <li><a href="#typesystem">Type System</a></li> - <li><a href="#dataflowinformation">Control-flow and Data-flow Information</a></li> - <li><a href="#registers">Registers</a></li> - <li><a href="#programmerinterface">Programmer Interface</a></li> - <li><a href="#codeemission">Machine Code Emission</a></li> -</ol> - -<div class="doc_text"> - <p><b>Written by Brian R. Gaeke</b></p> -</div> - -<!-- *********************************************************************** --> -<div class="doc_section"> - <a name="introduction">Introduction</a> -</div> -<!-- *********************************************************************** --> - -<div class="doc_text"> -<p>Whether you are a stranger to LLVM or not, and whether you are considering -using it for your projects or not, you may find it useful to understand how we -compare ourselves to other well-known compilers. The following list of points -should help you understand -- from our point of view -- some of the important -ways in which we see LLVM as different from other selected compilers and -code generation systems.</p> - -<p>At the moment, we only compare ourselves below to <a -href="http://gcc.gnu.org/">GCC</a> and <a -href="http://www.gnu.org/software/lightning/">GNU lightning</a>, but we will try -to revise and expand it as our knowledge and experience permit. Contributions are -welcome.</p> -</div> - -<!-- *********************************************************************** --> -<div class="doc_section"> - <a name="generalapplicability">General Applicability</a> -</div> -<!-- *********************************************************************** --> - -<div class="doc_text"> -<p>GNU lightning: Only currently usable for dynamic runtime emission of binary -machine code to memory. Supports one backend at a time.</p> - -<p>LLVM: Supports compilation of C and C++ (with more languages coming soon), -strong SSA-based optimization at compile-time, link-time, run-time, and -off-line, and multiple platform backends with Just-in-Time and ahead-of-time -compilation frameworks. (See our tech report on <a -href="http://llvm.cs.uiuc.edu/pubs/2003-09-30-LifelongOptimizationTR.html">Lifelong -Code Optimization</a> for more.)</p> - -<p>GCC: Many relatively mature platform backends support assembly-language code -generation from many source languages. No run-time compilation -support. Relatively weak optimization support.</p> -</div> - -<!-- *********************************************************************** --> -<div class="doc_section"> - <a name="typesystem">Type System</a> -</div> -<!-- *********************************************************************** --> - -<div class="doc_text"> -<p>GNU lightning: C integer types and "void *" are supported. No type checking -is performed. Explicit type casts are not typically necessary unless the -underlying machine-specific types are distinct (e.g., sign- or zero-extension is -apparently necessary, but casting "int" to "void *" would not be.) -Floating-point support may not work on all platforms (it does not appear to be -documented in the latest release).</p> - -<p>LLVM: Compositional type system based on C types, supporting structures, -opaque types, and C integer and floating point types. Explicit cast instructions -are required to transform a value from one type to another.</p> - -<p>GCC: Union of high-level types including those used in Pascal, C, C++, Ada, -Java, and FORTRAN.</p> -</div> - -<!-- *********************************************************************** --> -<div class="doc_section"> - <a name="dataflowinformation">Control-flow and Data-flow Information</a> -</div> -<!-- *********************************************************************** --> - -<div class="doc_text"> -<p>GNU lightning: No data-flow information encoded in the generated program. No -support for calculating CFG or def-use chains over generated programs.</p> - -<p>LLVM: Scalar values in Static Single-Assignment form; def-use chains and CFG -always implicitly available and automatically kept up to date.</p> - -<p>GCC: Trees and RTL do not directly encode data-flow info; but def-use chains -and CFGs can be calculated on the side. They are not automatically kept up to -date.</p> -</div> - -<!-- *********************************************************************** --> -<div class="doc_section"> - <a name="registers">Registers</a> -</div> -<!-- *********************************************************************** --> - -<div class="doc_text"> -<p>GNU lightning: Very small fixed register set -- it takes the least common -denominator of supported platforms; basically it inherits its tiny register set -from IA-32, unnecessarily crippling targets like PowerPC with a large register -set.</p> - -<p>LLVM: An infinite register set, reduced to a particular platform's finite -register set by register allocator.</p> - -<p>GCC: Trees and RTL provide an arbitrarily large set of values. Reduced to a -particular platform's finite register set by register allocator.</p> -</div> - -<!-- *********************************************************************** --> -<div class="doc_section"> - <a name="programmerinterface">Programmer Interface</a> -</div> -<!-- *********************************************************************** --> - -<div class="doc_text"> -<p>GNU lightning: Library interface based on C preprocessor macros that emit -binary code for a particular instruction to memory. No support for manipulating -code before emission.</p> - -<p>LLVM: Library interface based on classes representing platform-independent -intermediate code (Instruction) and platform-dependent code (MachineInstr) which -can be manipulated arbitrarily and then emitted to memory.</p> - -<p>GCC: Internal header file interface (tree.h) to abstract syntax trees, -representing roughly the union of all possible supported source-language -constructs; also, an internal header file interface (rtl.h, rtl.def) to a -low-level IR called RTL which represents roughly the union of all possible -target machine instructions.</p> -</div> - -<!-- *********************************************************************** --> -<div class="doc_section"> - <a name="codeemission">Machine Code Emission</a> -</div> -<!-- *********************************************************************** --> - -<div class="doc_text"> -<p>GNU lightning: Only supports binary machine code emission to memory.</p> - -<p>LLVM: Supports writing out assembly language to a file, and binary machine -code to memory, from the same back-end.</p> - -<p>GCC: Supports writing out assembly language to a file. No support for -emitting machine code to memory.</p> -</div> - -<!-- *********************************************************************** --> - -<hr> -<div class="doc_footer"> - <address>Brian R. Gaeke</address> - <a href="http://llvm.cs.uiuc.edu">The LLVM Compiler Infrastructure</a> - <br> - Last modified: $Date$ -</div> - -</body> -</html> |