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authormike-m <mikem.llvm@gmail.com>2010-05-06 23:45:43 +0000
committermike-m <mikem.llvm@gmail.com>2010-05-06 23:45:43 +0000
commit68cb31901c590cabceee6e6356d62c84142114cb (patch)
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Overhauled llvm/clang docs builds. Closes PR6613.
NOTE: 2nd part changeset for cfe trunk to follow. *** PRE-PATCH ISSUES ADDRESSED - clang api docs fail build from objdir - clang/llvm api docs collide in install PREFIX/ - clang/llvm main docs collide in install - clang/llvm main docs have full of hard coded destination assumptions and make use of absolute root in static html files; namely CommandGuide tools hard codes a website destination for cross references and some html cross references assume website root paths *** IMPROVEMENTS - bumped Doxygen from 1.4.x -> 1.6.3 - splits llvm/clang docs into 'main' and 'api' (doxygen) build trees - provide consistent, reliable doc builds for both main+api docs - support buid vs. install vs. website intentions - support objdir builds - document targets with 'make help' - correct clean and uninstall operations - use recursive dir delete only where absolutely necessary - added call function fn.RMRF which safeguards against botched 'rm -rf'; if any target (or any variable is evaluated) which attempts to remove any dirs which match a hard-coded 'safelist', a verbose error will be printed and make will error-stop. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@103213 91177308-0d34-0410-b5e6-96231b3b80d8
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-By Chris:
-
-LLVM has been designed with two primary goals in mind. First we strive to
-enable the best possible division of labor between static and dynamic
-compilers, and second, we need a flexible and powerful interface
-between these two complementary stages of compilation. We feel that
-providing a solution to these two goals will yield an excellent solution
-to the performance problem faced by modern architectures and programming
-languages.
-
-A key insight into current compiler and runtime systems is that a
-compiler may fall in anywhere in a "continuum of compilation" to do its
-job. On one side, scripting languages statically compile nothing and
-dynamically compile (or equivalently, interpret) everything. On the far
-other side, traditional static compilers process everything statically and
-nothing dynamically. These approaches have typically been seen as a
-tradeoff between performance and portability. On a deeper level, however,
-there are two reasons that optimal system performance may be obtained by a
-system somewhere in between these two extremes: Dynamic application
-behavior and social constraints.
-
-From a technical perspective, pure static compilation cannot ever give
-optimal performance in all cases, because applications have varying dynamic
-behavior that the static compiler cannot take into consideration. Even
-compilers that support profile guided optimization generate poor code in
-the real world, because using such optimization tunes that application
-to one particular usage pattern, whereas real programs (as opposed to
-benchmarks) often have several different usage patterns.
-
-On a social level, static compilation is a very shortsighted solution to
-the performance problem. Instruction set architectures (ISAs) continuously
-evolve, and each implementation of an ISA (a processor) must choose a set
-of tradeoffs that make sense in the market context that it is designed for.
-With every new processor introduced, the vendor faces two fundamental
-problems: First, there is a lag time between when a processor is introduced
-to when compilers generate quality code for the architecture. Secondly,
-even when compilers catch up to the new architecture there is often a large
-body of legacy code that was compiled for previous generations and will
-not or can not be upgraded. Thus a large percentage of code running on a
-processor may be compiled quite sub-optimally for the current
-characteristics of the dynamic execution environment.
-
-For these reasons, LLVM has been designed from the beginning as a long-term
-solution to these problems. Its design allows the large body of platform
-independent, static, program optimizations currently in compilers to be
-reused unchanged in their current form. It also provides important static
-type information to enable powerful dynamic and link time optimizations
-to be performed quickly and efficiently. This combination enables an
-increase in effective system performance for real world environments.